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Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/Makefile | 3 | ||||
| -rw-r--r-- | Documentation/DocBook/alsa-driver-api.tmpl | 109 | ||||
| -rw-r--r-- | Documentation/DocBook/writing-an-alsa-driver.tmpl | 6216 |
3 files changed, 6327 insertions, 1 deletions
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 1462ed86d40..a3a83d38f96 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -12,7 +12,8 @@ DOCBOOKS := z8530book.xml mcabook.xml device-drivers.xml \ kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \ gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \ genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \ - mac80211.xml debugobjects.xml sh.xml regulator.xml + mac80211.xml debugobjects.xml sh.xml regulator.xml \ + alsa-driver-api.xml writing-an-alsa-driver.xml ### # The build process is as follows (targets): diff --git a/Documentation/DocBook/alsa-driver-api.tmpl b/Documentation/DocBook/alsa-driver-api.tmpl new file mode 100644 index 00000000000..0230a96f056 --- /dev/null +++ b/Documentation/DocBook/alsa-driver-api.tmpl @@ -0,0 +1,109 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<!-- ****************************************************** --> +<!-- Header --> +<!-- ****************************************************** --> +<book id="ALSA-Driver-API"> + <bookinfo> + <title>The ALSA Driver API</title> + + <legalnotice> + <para> + This document is free; you can redistribute it and/or modify it + under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + </para> + + <para> + This document is distributed in the hope that it will be useful, + but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the + implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A + PARTICULAR PURPOSE</emphasis>. See the GNU General Public License + for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + </legalnotice> + + </bookinfo> + +<toc></toc> + + <chapter><title>Management of Cards and Devices</title> + <sect1><title>Card Management</title> +!Esound/core/init.c + </sect1> + <sect1><title>Device Components</title> +!Esound/core/device.c + </sect1> + <sect1><title>Module requests and Device File Entries</title> +!Esound/core/sound.c + </sect1> + <sect1><title>Memory Management Helpers</title> +!Esound/core/memory.c +!Esound/core/memalloc.c + </sect1> + </chapter> + <chapter><title>PCM API</title> + <sect1><title>PCM Core</title> +!Esound/core/pcm.c +!Esound/core/pcm_lib.c +!Esound/core/pcm_native.c + </sect1> + <sect1><title>PCM Format Helpers</title> +!Esound/core/pcm_misc.c + </sect1> + <sect1><title>PCM Memory Management</title> +!Esound/core/pcm_memory.c + </sect1> + </chapter> + <chapter><title>Control/Mixer API</title> + <sect1><title>General Control Interface</title> +!Esound/core/control.c + </sect1> + <sect1><title>AC97 Codec API</title> +!Esound/pci/ac97/ac97_codec.c +!Esound/pci/ac97/ac97_pcm.c + </sect1> + <sect1><title>Virtual Master Control API</title> +!Esound/core/vmaster.c +!Iinclude/sound/control.h + </sect1> + </chapter> + <chapter><title>MIDI API</title> + <sect1><title>Raw MIDI API</title> +!Esound/core/rawmidi.c + </sect1> + <sect1><title>MPU401-UART API</title> +!Esound/drivers/mpu401/mpu401_uart.c + </sect1> + </chapter> + <chapter><title>Proc Info API</title> + <sect1><title>Proc Info Interface</title> +!Esound/core/info.c + </sect1> + </chapter> + <chapter><title>Miscellaneous Functions</title> + <sect1><title>Hardware-Dependent Devices API</title> +!Esound/core/hwdep.c + </sect1> + <sect1><title>Jack Abstraction Layer API</title> +!Esound/core/jack.c + </sect1> + <sect1><title>ISA DMA Helpers</title> +!Esound/core/isadma.c + </sect1> + <sect1><title>Other Helper Macros</title> +!Iinclude/sound/core.h + </sect1> + </chapter> + +</book> diff --git a/Documentation/DocBook/writing-an-alsa-driver.tmpl b/Documentation/DocBook/writing-an-alsa-driver.tmpl new file mode 100644 index 00000000000..46b08fef374 --- /dev/null +++ b/Documentation/DocBook/writing-an-alsa-driver.tmpl @@ -0,0 +1,6216 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<!-- ****************************************************** --> +<!-- Header --> +<!-- ****************************************************** --> +<book id="Writing-an-ALSA-Driver"> + <bookinfo> + <title>Writing an ALSA Driver</title> + <author> + <firstname>Takashi</firstname> + <surname>Iwai</surname> + <affiliation> + <address> + <email>tiwai@suse.de</email> + </address> + </affiliation> + </author> + + <date>Oct 15, 2007</date> + <edition>0.3.7</edition> + + <abstract> + <para> + This document describes how to write an ALSA (Advanced Linux + Sound Architecture) driver. + </para> + </abstract> + + <legalnotice> + <para> + Copyright (c) 2002-2005 Takashi Iwai <email>tiwai@suse.de</email> + </para> + + <para> + This document is free; you can redistribute it and/or modify it + under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + </para> + + <para> + This document is distributed in the hope that it will be useful, + but <emphasis>WITHOUT ANY WARRANTY</emphasis>; without even the + implied warranty of <emphasis>MERCHANTABILITY or FITNESS FOR A + PARTICULAR PURPOSE</emphasis>. See the GNU General Public License + for more details. + </para> + + <para> + You should have received a copy of the GNU General Public + License along with this program; if not, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, + MA 02111-1307 USA + </para> + </legalnotice> + + </bookinfo> + +<!-- ****************************************************** --> +<!-- Preface --> +<!-- ****************************************************** --> + <preface id="preface"> + <title>Preface</title> + <para> + This document describes how to write an + <ulink url="http://www.alsa-project.org/"><citetitle> + ALSA (Advanced Linux Sound Architecture)</citetitle></ulink> + driver. The document focuses mainly on PCI soundcards. + In the case of other device types, the API might + be different, too. However, at least the ALSA kernel API is + consistent, and therefore it would be still a bit help for + writing them. + </para> + + <para> + This document targets people who already have enough + C language skills and have basic linux kernel programming + knowledge. This document doesn't explain the general + topic of linux kernel coding and doesn't cover low-level + driver implementation details. It only describes + the standard way to write a PCI sound driver on ALSA. + </para> + + <para> + If you are already familiar with the older ALSA ver.0.5.x API, you + can check the drivers such as <filename>sound/pci/es1938.c</filename> or + <filename>sound/pci/maestro3.c</filename> which have also almost the same + code-base in the ALSA 0.5.x tree, so you can compare the differences. + </para> + + <para> + This document is still a draft version. Any feedback and + corrections, please!! + </para> + </preface> + + +<!-- ****************************************************** --> +<!-- File Tree Structure --> +<!-- ****************************************************** --> + <chapter id="file-tree"> + <title>File Tree Structure</title> + + <section id="file-tree-general"> + <title>General</title> + <para> + The ALSA drivers are provided in two ways. + </para> + + <para> + One is the trees provided as a tarball or via cvs from the + ALSA's ftp site, and another is the 2.6 (or later) Linux kernel + tree. To synchronize both, the ALSA driver tree is split into + two different trees: alsa-kernel and alsa-driver. The former + contains purely the source code for the Linux 2.6 (or later) + tree. This tree is designed only for compilation on 2.6 or + later environment. The latter, alsa-driver, contains many subtle + files for compiling ALSA drivers outside of the Linux kernel tree, + wrapper functions for older 2.2 and 2.4 kernels, to adapt the latest kernel API, + and additional drivers which are still in development or in + tests. The drivers in alsa-driver tree will be moved to + alsa-kernel (and eventually to the 2.6 kernel tree) when they are + finished and confirmed to work fine. + </para> + + <para> + The file tree structure of ALSA driver is depicted below. Both + alsa-kernel and alsa-driver have almost the same file + structure, except for <quote>core</quote> directory. It's + named as <quote>acore</quote> in alsa-driver tree. + + <example> + <title>ALSA File Tree Structure</title> + <literallayout> + sound + /core + /oss + /seq + /oss + /instr + /ioctl32 + /include + /drivers + /mpu401 + /opl3 + /i2c + /l3 + /synth + /emux + /pci + /(cards) + /isa + /(cards) + /arm + /ppc + /sparc + /usb + /pcmcia /(cards) + /oss + </literallayout> + </example> + </para> + </section> + + <section id="file-tree-core-directory"> + <title>core directory</title> + <para> + This directory contains the middle layer which is the heart + of ALSA drivers. In this directory, the native ALSA modules are + stored. The sub-directories contain different modules and are + dependent upon the kernel config. + </para> + + <section id="file-tree-core-directory-oss"> + <title>core/oss</title> + + <para> + The codes for PCM and mixer OSS emulation modules are stored + in this directory. The rawmidi OSS emulation is included in + the ALSA rawmidi code since it's quite small. The sequencer + code is stored in <filename>core/seq/oss</filename> directory (see + <link linkend="file-tree-core-directory-seq-oss"><citetitle> + below</citetitle></link>). + </para> + </section> + + <section id="file-tree-core-directory-ioctl32"> + <title>core/ioctl32</title> + + <para> + This directory contains the 32bit-ioctl wrappers for 64bit + architectures such like x86-64, ppc64 and sparc64. For 32bit + and alpha architectures, these are not compiled. + </para> + </section> + + <section id="file-tree-core-directory-seq"> + <title>core/seq</title> + <para> + This directory and its sub-directories are for the ALSA + sequencer. This directory contains the sequencer core and + primary sequencer modules such like snd-seq-midi, + snd-seq-virmidi, etc. They are compiled only when + <constant>CONFIG_SND_SEQUENCER</constant> is set in the kernel + config. + </para> + </section> + + <section id="file-tree-core-directory-seq-oss"> + <title>core/seq/oss</title> + <para> + This contains the OSS sequencer emulation codes. + </para> + </section> + + <section id="file-tree-core-directory-deq-instr"> + <title>core/seq/instr</title> + <para> + This directory contains the modules for the sequencer + instrument layer. + </para> + </section> + </section> + + <section id="file-tree-include-directory"> + <title>include directory</title> + <para> + This is the place for the public header files of ALSA drivers, + which are to be exported to user-space, or included by + several files at different directories. Basically, the private + header files should not be placed in this directory, but you may + still find files there, due to historical reasons :) + </para> + </section> + + <section id="file-tree-drivers-directory"> + <title>drivers directory</title> + <para> + This directory contains code shared among different drivers + on different architectures. They are hence supposed not to be + architecture-specific. + For example, the dummy pcm driver and the serial MIDI + driver are found in this directory. In the sub-directories, + there is code for components which are independent from + bus and cpu architectures. + </para> + + <section id="file-tree-drivers-directory-mpu401"> + <title>drivers/mpu401</title> + <para> + The MPU401 and MPU401-UART modules are stored here. + </para> + </section> + + <section id="file-tree-drivers-directory-opl3"> + <title>drivers/opl3 and opl4</title> + <para> + The OPL3 and OPL4 FM-synth stuff is found here. + </para> + </section> + </section> + + <section id="file-tree-i2c-directory"> + <title>i2c directory</title> + <para> + This contains the ALSA i2c components. + </para> + + <para> + Although there is a standard i2c layer on Linux, ALSA has its + own i2c code for some cards, because the soundcard needs only a + simple operation and the standard i2c API is too complicated for + such a purpose. + </para> + + <section id="file-tree-i2c-directory-l3"> + <title>i2c/l3</title> + <para> + This is a sub-directory for ARM L3 i2c. + </para> + </section> + </section> + + <section id="file-tree-synth-directory"> + <title>synth directory</title> + <para> + This contains the synth middle-level modules. + </para> + + <para> + So far, there is only Emu8000/Emu10k1 synth driver under + the <filename>synth/emux</filename> sub-directory. + </para> + </section> + + <section id="file-tree-pci-directory"> + <title>pci directory</title> + <para> + This directory and its sub-directories hold the top-level card modules + for PCI soundcards and the code specific to the PCI BUS. + </para> + + <para> + The drivers compiled from a single file are stored directly + in the pci directory, while the drivers with several source files are + stored on their own sub-directory (e.g. emu10k1, ice1712). + </para> + </section> + + <section id="file-tree-isa-directory"> + <title>isa directory</title> + <para> + This directory and its sub-directories hold the top-level card modules + for ISA soundcards. + </para> + </section> + + <section id="file-tree-arm-ppc-sparc-directories"> + <title>arm, ppc, and sparc directories</title> + <para> + They are used for top-level card modules which are + specific to one of these architectures. + </para> + </section> + + <section id="file-tree-usb-directory"> + <title>usb directory</title> + <para> + This directory contains the USB-audio driver. In the latest version, the + USB MIDI driver is integrated in the usb-audio driver. + </para> + </section> + + <section id="file-tree-pcmcia-directory"> + <title>pcmcia directory</title> + <para> + The PCMCIA, especially PCCard drivers will go here. CardBus + drivers will be in the pci directory, because their API is identical + to that of standard PCI cards. + </para> + </section> + + <section id="file-tree-oss-directory"> + <title>oss directory</title> + <para> + The OSS/Lite source files are stored here in Linux 2.6 (or + later) tree. In the ALSA driver tarball, this directory is empty, + of course :) + </para> + </section> + </chapter> + + +<!-- ****************************************************** --> +<!-- Basic Flow for PCI Drivers --> +<!-- ****************************************************** --> + <chapter id="basic-flow"> + <title>Basic Flow for PCI Drivers</title> + + <section id="basic-flow-outline"> + <title>Outline</title> + <para> + The minimum flow for PCI soundcards is as follows: + + <itemizedlist> + <listitem><para>define the PCI ID table (see the section + <link linkend="pci-resource-entries"><citetitle>PCI Entries + </citetitle></link>).</para></listitem> + <listitem><para>create <function>probe()</function> callback.</para></listitem> + <listitem><para>create <function>remove()</function> callback.</para></listitem> + <listitem><para>create a <structname>pci_driver</structname> structure + containing the three pointers above.</para></listitem> + <listitem><para>create an <function>init()</function> function just calling + the <function>pci_register_driver()</function> to register the pci_driver table + defined above.</para></listitem> + <listitem><para>create an <function>exit()</function> function to call + the <function>pci_unregister_driver()</function> function.</para></listitem> + </itemizedlist> + </para> + </section> + + <section id="basic-flow-example"> + <title>Full Code Example</title> + <para> + The code example is shown below. Some parts are kept + unimplemented at this moment but will be filled in the + next sections. The numbers in the comment lines of the + <function>snd_mychip_probe()</function> function + refer to details explained in the following section. + + <example> + <title>Basic Flow for PCI Drivers - Example</title> + <programlisting> +<![CDATA[ + #include <linux/init.h> + #include <linux/pci.h> + #include <linux/slab.h> + #include <sound/core.h> + #include <sound/initval.h> + + /* module parameters (see "Module Parameters") */ + /* SNDRV_CARDS: maximum number of cards supported by this module */ + static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; + static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; + static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; + + /* definition of the chip-specific record */ + struct mychip { + struct snd_card *card; + /* the rest of the implementation will be in section + * "PCI Resource Management" + */ + }; + + /* chip-specific destructor + * (see "PCI Resource Management") + */ + static int snd_mychip_free(struct mychip *chip) + { + .... /* will be implemented later... */ + } + + /* component-destructor + * (see "Management of Cards and Components") + */ + static int snd_mychip_dev_free(struct snd_device *device) + { + return snd_mychip_free(device->device_data); + } + + /* chip-specific constructor + * (see "Management of Cards and Components") + */ + static int __devinit snd_mychip_create(struct snd_card *card, + struct pci_dev *pci, + struct mychip **rchip) + { + struct mychip *chip; + int err; + static struct snd_device_ops ops = { + .dev_free = snd_mychip_dev_free, + }; + + *rchip = NULL; + + /* check PCI availability here + * (see "PCI Resource Management") + */ + .... + + /* allocate a chip-specific data with zero filled */ + chip = kzalloc(sizeof(*chip), GFP_KERNEL); + if (chip == NULL) + return -ENOMEM; + + chip->card = card; + + /* rest of initialization here; will be implemented + * later, see "PCI Resource Management" + */ + .... + + err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); + if (err < 0) { + snd_mychip_free(chip); + return err; + } + + snd_card_set_dev(card, &pci->dev); + + *rchip = chip; + return 0; + } + + /* constructor -- see "Constructor" sub-section */ + static int __devinit snd_mychip_probe(struct pci_dev *pci, + const struct pci_device_id *pci_id) + { + static int dev; + struct snd_card *card; + struct mychip *chip; + int err; + + /* (1) */ + if (dev >= SNDRV_CARDS) + return -ENODEV; + if (!enable[dev]) { + dev++; + return -ENOENT; + } + + /* (2) */ + err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card); + if (err < 0) + return err; + + /* (3) */ + err = snd_mychip_create(card, pci, &chip); + if (err < 0) { + snd_card_free(card); + return err; + } + + /* (4) */ + strcpy(card->driver, "My Chip"); + strcpy(card->shortname, "My Own Chip 123"); + sprintf(card->longname, "%s at 0x%lx irq %i", + card->shortname, chip->ioport, chip->irq); + + /* (5) */ + .... /* implemented later */ + + /* (6) */ + err = snd_card_register(card); + if (err < 0) { + snd_card_free(card); + return err; + } + + /* (7) */ + pci_set_drvdata(pci, card); + dev++; + return 0; + } + + /* destructor -- see the "Destructor" sub-section */ + static void __devexit snd_mychip_remove(struct pci_dev *pci) + { + snd_card_free(pci_get_drvdata(pci)); + pci_set_drvdata(pci, NULL); + } +]]> + </programlisting> + </example> + </para> + </section> + + <section id="basic-flow-constructor"> + <title>Constructor</title> + <para> + The real constructor of PCI drivers is the <function>probe</function> callback. + The <function>probe</function> callback and other component-constructors which are called + from the <function>probe</function> callback should be defined with + the <parameter>__devinit</parameter> prefix. You + cannot use the <parameter>__init</parameter> prefix for them, + because any PCI device could be a hotplug device. + </para> + + <para> + In the <function>probe</function> callback, the following scheme is often used. + </para> + + <section id="basic-flow-constructor-device-index"> + <title>1) Check and increment the device index.</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + static int dev; + .... + if (dev >= SNDRV_CARDS) + return -ENODEV; + if (!enable[dev]) { + dev++; + return -ENOENT; + } +]]> + </programlisting> + </informalexample> + + where enable[dev] is the module option. + </para> + + <para> + Each time the <function>probe</function> callback is called, check the + availability of the device. If not available, simply increment + the device index and returns. dev will be incremented also + later (<link + linkend="basic-flow-constructor-set-pci"><citetitle>step + 7</citetitle></link>). + </para> + </section> + + <section id="basic-flow-constructor-create-card"> + <title>2) Create a card instance</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + struct snd_card *card; + int err; + .... + err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The details will be explained in the section + <link linkend="card-management-card-instance"><citetitle> + Management of Cards and Components</citetitle></link>. + </para> + </section> + + <section id="basic-flow-constructor-create-main"> + <title>3) Create a main component</title> + <para> + In this part, the PCI resources are allocated. + + <informalexample> + <programlisting> +<![CDATA[ + struct mychip *chip; + .... + err = snd_mychip_create(card, pci, &chip); + if (err < 0) { + snd_card_free(card); + return err; + } +]]> + </programlisting> + </informalexample> + + The details will be explained in the section <link + linkend="pci-resource"><citetitle>PCI Resource + Management</citetitle></link>. + </para> + </section> + + <section id="basic-flow-constructor-main-component"> + <title>4) Set the driver ID and name strings.</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + strcpy(card->driver, "My Chip"); + strcpy(card->shortname, "My Own Chip 123"); + sprintf(card->longname, "%s at 0x%lx irq %i", + card->shortname, chip->ioport, chip->irq); +]]> + </programlisting> + </informalexample> + + The driver field holds the minimal ID string of the + chip. This is used by alsa-lib's configurator, so keep it + simple but unique. + Even the same driver can have different driver IDs to + distinguish the functionality of each chip type. + </para> + + <para> + The shortname field is a string shown as more verbose + name. The longname field contains the information + shown in <filename>/proc/asound/cards</filename>. + </para> + </section> + + <section id="basic-flow-constructor-create-other"> + <title>5) Create other components, such as mixer, MIDI, etc.</title> + <para> + Here you define the basic components such as + <link linkend="pcm-interface"><citetitle>PCM</citetitle></link>, + mixer (e.g. <link linkend="api-ac97"><citetitle>AC97</citetitle></link>), + MIDI (e.g. <link linkend="midi-interface"><citetitle>MPU-401</citetitle></link>), + and other interfaces. + Also, if you want a <link linkend="proc-interface"><citetitle>proc + file</citetitle></link>, define it here, too. + </para> + </section> + + <section id="basic-flow-constructor-register-card"> + <title>6) Register the card instance.</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + err = snd_card_register(card); + if (err < 0) { + snd_card_free(card); + return err; + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + Will be explained in the section <link + linkend="card-management-registration"><citetitle>Management + of Cards and Components</citetitle></link>, too. + </para> + </section> + + <section id="basic-flow-constructor-set-pci"> + <title>7) Set the PCI driver data and return zero.</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + pci_set_drvdata(pci, card); + dev++; + return 0; +]]> + </programlisting> + </informalexample> + + In the above, the card record is stored. This pointer is + used in the remove callback and power-management + callbacks, too. + </para> + </section> + </section> + + <section id="basic-flow-destructor"> + <title>Destructor</title> + <para> + The destructor, remove callback, simply releases the card + instance. Then the ALSA middle layer will release all the + attached components automatically. + </para> + + <para> + It would be typically like the following: + + <informalexample> + <programlisting> +<![CDATA[ + static void __devexit snd_mychip_remove(struct pci_dev *pci) + { + snd_card_free(pci_get_drvdata(pci)); + pci_set_drvdata(pci, NULL); + } +]]> + </programlisting> + </informalexample> + + The above code assumes that the card pointer is set to the PCI + driver data. + </para> + </section> + + <section id="basic-flow-header-files"> + <title>Header Files</title> + <para> + For the above example, at least the following include files + are necessary. + + <informalexample> + <programlisting> +<![CDATA[ + #include <linux/init.h> + #include <linux/pci.h> + #include <linux/slab.h> + #include <sound/core.h> + #include <sound/initval.h> +]]> + </programlisting> + </informalexample> + + where the last one is necessary only when module options are + defined in the source file. If the code is split into several + files, the files without module options don't need them. + </para> + + <para> + In addition to these headers, you'll need + <filename><linux/interrupt.h></filename> for interrupt + handling, and <filename><asm/io.h></filename> for I/O + access. If you use the <function>mdelay()</function> or + <function>udelay()</function> functions, you'll need to include + <filename><linux/delay.h></filename> too. + </para> + + <para> + The ALSA interfaces like the PCM and control APIs are defined in other + <filename><sound/xxx.h></filename> header files. + They have to be included after + <filename><sound/core.h></filename>. + </para> + + </section> + </chapter> + + +<!-- ****************************************************** --> +<!-- Management of Cards and Components --> +<!-- ****************************************************** --> + <chapter id="card-management"> + <title>Management of Cards and Components</title> + + <section id="card-management-card-instance"> + <title>Card Instance</title> + <para> + For each soundcard, a <quote>card</quote> record must be allocated. + </para> + + <para> + A card record is the headquarters of the soundcard. It manages + the whole list of devices (components) on the soundcard, such as + PCM, mixers, MIDI, synthesizer, and so on. Also, the card + record holds the ID and the name strings of the card, manages + the root of proc files, and controls the power-management states + and hotplug disconnections. The component list on the card + record is used to manage the correct release of resources at + destruction. + </para> + + <para> + As mentioned above, to create a card instance, call + <function>snd_card_create()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_card *card; + int err; + err = snd_card_create(index, id, module, extra_size, &card); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The function takes five arguments, the card-index number, the + id string, the module pointer (usually + <constant>THIS_MODULE</constant>), + the size of extra-data space, and the pointer to return the + card instance. The extra_size argument is used to + allocate card->private_data for the + chip-specific data. Note that these data + are allocated by <function>snd_card_create()</function>. + </para> + </section> + + <section id="card-management-component"> + <title>Components</title> + <para> + After the card is created, you can attach the components + (devices) to the card instance. In an ALSA driver, a component is + represented as a struct <structname>snd_device</structname> object. + A component can be a PCM instance, a control interface, a raw + MIDI interface, etc. Each such instance has one component + entry. + </para> + + <para> + A component can be created via + <function>snd_device_new()</function> function. + + <informalexample> + <programlisting> +<![CDATA[ + snd_device_new(card, SNDRV_DEV_XXX, chip, &ops); +]]> + </programlisting> + </informalexample> + </para> + + <para> + This takes the card pointer, the device-level + (<constant>SNDRV_DEV_XXX</constant>), the data pointer, and the + callback pointers (<parameter>&ops</parameter>). The + device-level defines the type of components and the order of + registration and de-registration. For most components, the + device-level is already defined. For a user-defined component, + you can use <constant>SNDRV_DEV_LOWLEVEL</constant>. + </para> + + <para> + This function itself doesn't allocate the data space. The data + must be allocated manually beforehand, and its pointer is passed + as the argument. This pointer is used as the + (<parameter>chip</parameter> identifier in the above example) + for the instance. + </para> + + <para> + Each pre-defined ALSA component such as ac97 and pcm calls + <function>snd_device_new()</function> inside its + constructor. The destructor for each component is defined in the + callback pointers. Hence, you don't need to take care of + calling a destructor for such a component. + </para> + + <para> + If you wish to create your own component, you need to + set the destructor function to the dev_free callback in + the <parameter>ops</parameter>, so that it can be released + automatically via <function>snd_card_free()</function>. + The next example will show an implementation of chip-specific + data. + </para> + </section> + + <section id="card-management-chip-specific"> + <title>Chip-Specific Data</title> + <para> + Chip-specific information, e.g. the I/O port address, its + resource pointer, or the irq number, is stored in the + chip-specific record. + + <informalexample> + <programlisting> +<![CDATA[ + struct mychip { + .... + }; +]]> + </programlisting> + </informalexample> + </para> + + <para> + In general, there are two ways of allocating the chip record. + </para> + + <section id="card-management-chip-specific-snd-card-new"> + <title>1. Allocating via <function>snd_card_create()</function>.</title> + <para> + As mentioned above, you can pass the extra-data-length + to the 4th argument of <function>snd_card_create()</function>, i.e. + + <informalexample> + <programlisting> +<![CDATA[ + err = snd_card_create(index[dev], id[dev], THIS_MODULE, + sizeof(struct mychip), &card); +]]> + </programlisting> + </informalexample> + + struct <structname>mychip</structname> is the type of the chip record. + </para> + + <para> + In return, the allocated record can be accessed as + + <informalexample> + <programlisting> +<![CDATA[ + struct mychip *chip = card->private_data; +]]> + </programlisting> + </informalexample> + + With this method, you don't have to allocate twice. + The record is released together with the card instance. + </para> + </section> + + <section id="card-management-chip-specific-allocate-extra"> + <title>2. Allocating an extra device.</title> + + <para> + After allocating a card instance via + <function>snd_card_create()</function> (with + <constant>0</constant> on the 4th arg), call + <function>kzalloc()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_card *card; + struct mychip *chip; + err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card); + ..... + chip = kzalloc(sizeof(*chip), GFP_KERNEL); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The chip record should have the field to hold the card + pointer at least, + + <informalexample> + <programlisting> +<![CDATA[ + struct mychip { + struct snd_card *card; + .... + }; +]]> + </programlisting> + </informalexample> + </para> + + <para> + Then, set the card pointer in the returned chip instance. + + <informalexample> + <programlisting> +<![CDATA[ + chip->card = card; +]]> + </programlisting> + </informalexample> + </para> + + <para> + Next, initialize the fields, and register this chip + record as a low-level device with a specified + <parameter>ops</parameter>, + + <informalexample> + <programlisting> +<![CDATA[ + static struct snd_device_ops ops = { + .dev_free = snd_mychip_dev_free, + }; + .... + snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); +]]> + </programlisting> + </informalexample> + + <function>snd_mychip_dev_free()</function> is the + device-destructor function, which will call the real + destructor. + </para> + + <para> + <informalexample> + <programlisting> +<![CDATA[ + static int snd_mychip_dev_free(struct snd_device *device) + { + return snd_mychip_free(device->device_data); + } +]]> + </programlisting> + </informalexample> + + where <function>snd_mychip_free()</function> is the real destructor. + </para> + </section> + </section> + + <section id="card-management-registration"> + <title>Registration and Release</title> + <para> + After all components are assigned, register the card instance + by calling <function>snd_card_register()</function>. Access + to the device files is enabled at this point. That is, before + <function>snd_card_register()</function> is called, the + components are safely inaccessible from external side. If this + call fails, exit the probe function after releasing the card via + <function>snd_card_free()</function>. + </para> + + <para> + For releasing the card instance, you can call simply + <function>snd_card_free()</function>. As mentioned earlier, all + components are released automatically by this call. + </para> + + <para> + As further notes, the destructors (both + <function>snd_mychip_dev_free</function> and + <function>snd_mychip_free</function>) cannot be defined with + the <parameter>__devexit</parameter> prefix, because they may be + called from the constructor, too, at the false path. + </para> + + <para> + For a device which allows hotplugging, you can use + <function>snd_card_free_when_closed</function>. This one will + postpone the destruction until all devices are closed. + </para> + + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- PCI Resource Management --> +<!-- ****************************************************** --> + <chapter id="pci-resource"> + <title>PCI Resource Management</title> + + <section id="pci-resource-example"> + <title>Full Code Example</title> + <para> + In this section, we'll complete the chip-specific constructor, + destructor and PCI entries. Example code is shown first, + below. + + <example> + <title>PCI Resource Management Example</title> + <programlisting> +<![CDATA[ + struct mychip { + struct snd_card *card; + struct pci_dev *pci; + + unsigned long port; + int irq; + }; + + static int snd_mychip_free(struct mychip *chip) + { + /* disable hardware here if any */ + .... /* (not implemented in this document) */ + + /* release the irq */ + if (chip->irq >= 0) + free_irq(chip->irq, chip); + /* release the I/O ports & memory */ + pci_release_regions(chip->pci); + /* disable the PCI entry */ + pci_disable_device(chip->pci); + /* release the data */ + kfree(chip); + return 0; + } + + /* chip-specific constructor */ + static int __devinit snd_mychip_create(struct snd_card *card, + struct pci_dev *pci, + struct mychip **rchip) + { + struct mychip *chip; + int err; + static struct snd_device_ops ops = { + .dev_free = snd_mychip_dev_free, + }; + + *rchip = NULL; + + /* initialize the PCI entry */ + err = pci_enable_device(pci); + if (err < 0) + return err; + /* check PCI availability (28bit DMA) */ + if (pci_set_dma_mask(pci, DMA_28BIT_MASK) < 0 || + pci_set_consistent_dma_mask(pci, DMA_28BIT_MASK) < 0) { + printk(KERN_ERR "error to set 28bit mask DMA\n"); + pci_disable_device(pci); + return -ENXIO; + } + + chip = kzalloc(sizeof(*chip), GFP_KERNEL); + if (chip == NULL) { + pci_disable_device(pci); + return -ENOMEM; + } + + /* initialize the stuff */ + chip->card = card; + chip->pci = pci; + chip->irq = -1; + + /* (1) PCI resource allocation */ + err = pci_request_regions(pci, "My Chip"); + if (err < 0) { + kfree(chip); + pci_disable_device(pci); + return err; + } + chip->port = pci_resource_start(pci, 0); + if (request_irq(pci->irq, snd_mychip_interrupt, + IRQF_SHARED, "My Chip", chip)) { + printk(KERN_ERR "cannot grab irq %d\n", pci->irq); + snd_mychip_free(chip); + return -EBUSY; + } + chip->irq = pci->irq; + + /* (2) initialization of the chip hardware */ + .... /* (not implemented in this document) */ + + err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, chip, &ops); + if (err < 0) { + snd_mychip_free(chip); + return err; + } + + snd_card_set_dev(card, &pci->dev); + + *rchip = chip; + return 0; + } + + /* PCI IDs */ + static struct pci_device_id snd_mychip_ids[] = { + { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, + PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, + .... + { 0, } + }; + MODULE_DEVICE_TABLE(pci, snd_mychip_ids); + + /* pci_driver definition */ + static struct pci_driver driver = { + .name = "My Own Chip", + .id_table = snd_mychip_ids, + .probe = snd_mychip_probe, + .remove = __devexit_p(snd_mychip_remove), + }; + + /* module initialization */ + static int __init alsa_card_mychip_init(void) + { + return pci_register_driver(&driver); + } + + /* module clean up */ + static void __exit alsa_card_mychip_exit(void) + { + pci_unregister_driver(&driver); + } + + module_init(alsa_card_mychip_init) + module_exit(alsa_card_mychip_exit) + + EXPORT_NO_SYMBOLS; /* for old kernels only */ +]]> + </programlisting> + </example> + </para> + </section> + + <section id="pci-resource-some-haftas"> + <title>Some Hafta's</title> + <para> + The allocation of PCI resources is done in the + <function>probe()</function> function, and usually an extra + <function>xxx_create()</function> function is written for this + purpose. + </para> + + <para> + In the case of PCI devices, you first have to call + the <function>pci_enable_device()</function> function before + allocating resources. Also, you need to set the proper PCI DMA + mask to limit the accessed I/O range. In some cases, you might + need to call <function>pci_set_master()</function> function, + too. + </para> + + <para> + Suppose the 28bit mask, and the code to be added would be like: + + <informalexample> + <programlisting> +<![CDATA[ + err = pci_enable_device(pci); + if (err < 0) + return err; + if (pci_set_dma_mask(pci, DMA_28BIT_MASK) < 0 || + pci_set_consistent_dma_mask(pci, DMA_28BIT_MASK) < 0) { + printk(KERN_ERR "error to set 28bit mask DMA\n"); + pci_disable_device(pci); + return -ENXIO; + } + +]]> + </programlisting> + </informalexample> + </para> + </section> + + <section id="pci-resource-resource-allocation"> + <title>Resource Allocation</title> + <para> + The allocation of I/O ports and irqs is done via standard kernel + functions. Unlike ALSA ver.0.5.x., there are no helpers for + that. And these resources must be released in the destructor + function (see below). Also, on ALSA 0.9.x, you don't need to + allocate (pseudo-)DMA for PCI like in ALSA 0.5.x. + </para> + + <para> + Now assume that the PCI device has an I/O port with 8 bytes + and an interrupt. Then struct <structname>mychip</structname> will have the + following fields: + + <informalexample> + <programlisting> +<![CDATA[ + struct mychip { + struct snd_card *card; + + unsigned long port; + int irq; + }; +]]> + </programlisting> + </informalexample> + </para> + + <para> + For an I/O port (and also a memory region), you need to have + the resource pointer for the standard resource management. For + an irq, you have to keep only the irq number (integer). But you + need to initialize this number as -1 before actual allocation, + since irq 0 is valid. The port address and its resource pointer + can be initialized as null by + <function>kzalloc()</function> automatically, so you + don't have to take care of resetting them. + </para> + + <para> + The allocation of an I/O port is done like this: + + <informalexample> + <programlisting> +<![CDATA[ + err = pci_request_regions(pci, "My Chip"); + if (err < 0) { + kfree(chip); + pci_disable_device(pci); + return err; + } + chip->port = pci_resource_start(pci, 0); +]]> + </programlisting> + </informalexample> + </para> + + <para> + <!-- obsolete --> + It will reserve the I/O port region of 8 bytes of the given + PCI device. The returned value, chip->res_port, is allocated + via <function>kmalloc()</function> by + <function>request_region()</function>. The pointer must be + released via <function>kfree()</function>, but there is a + problem with this. This issue will be explained later. + </para> + + <para> + The allocation of an interrupt source is done like this: + + <informalexample> + <programlisting> +<![CDATA[ + if (request_irq(pci->irq, snd_mychip_interrupt, + IRQF_SHARED, "My Chip", chip)) { + printk(KERN_ERR "cannot grab irq %d\n", pci->irq); + snd_mychip_free(chip); + return -EBUSY; + } + chip->irq = pci->irq; +]]> + </programlisting> + </informalexample> + + where <function>snd_mychip_interrupt()</function> is the + interrupt handler defined <link + linkend="pcm-interface-interrupt-handler"><citetitle>later</citetitle></link>. + Note that chip->irq should be defined + only when <function>request_irq()</function> succeeded. + </para> + + <para> + On the PCI bus, interrupts can be shared. Thus, + <constant>IRQF_SHARED</constant> is used as the interrupt flag of + <function>request_irq()</function>. + </para> + + <para> + The last argument of <function>request_irq()</function> is the + data pointer passed to the interrupt handler. Usually, the + chip-specific record is used for that, but you can use what you + like, too. + </para> + + <para> + I won't give details about the interrupt handler at this + point, but at least its appearance can be explained now. The + interrupt handler looks usually like the following: + + <informalexample> + <programlisting> +<![CDATA[ + static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) + { + struct mychip *chip = dev_id; + .... + return IRQ_HANDLED; + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + Now let's write the corresponding destructor for the resources + above. The role of destructor is simple: disable the hardware + (if already activated) and release the resources. So far, we + have no hardware part, so the disabling code is not written here. + </para> + + <para> + To release the resources, the <quote>check-and-release</quote> + method is a safer way. For the interrupt, do like this: + + <informalexample> + <programlisting> +<![CDATA[ + if (chip->irq >= 0) + free_irq(chip->irq, chip); +]]> + </programlisting> + </informalexample> + + Since the irq number can start from 0, you should initialize + chip->irq with a negative value (e.g. -1), so that you can + check the validity of the irq number as above. + </para> + + <para> + When you requested I/O ports or memory regions via + <function>pci_request_region()</function> or + <function>pci_request_regions()</function> like in this example, + release the resource(s) using the corresponding function, + <function>pci_release_region()</function> or + <function>pci_release_regions()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + pci_release_regions(chip->pci); +]]> + </programlisting> + </informalexample> + </para> + + <para> + When you requested manually via <function>request_region()</function> + or <function>request_mem_region</function>, you can release it via + <function>release_resource()</function>. Suppose that you keep + the resource pointer returned from <function>request_region()</function> + in chip->res_port, the release procedure looks like: + + <informalexample> + <programlisting> +<![CDATA[ + release_and_free_resource(chip->res_port); +]]> + </programlisting> + </informalexample> + </para> + + <para> + Don't forget to call <function>pci_disable_device()</function> + before the end. + </para> + + <para> + And finally, release the chip-specific record. + + <informalexample> + <programlisting> +<![CDATA[ + kfree(chip); +]]> + </programlisting> + </informalexample> + </para> + + <para> + Again, remember that you cannot + use the <parameter>__devexit</parameter> prefix for this destructor. + </para> + + <para> + We didn't implement the hardware disabling part in the above. + If you need to do this, please note that the destructor may be + called even before the initialization of the chip is completed. + It would be better to have a flag to skip hardware disabling + if the hardware was not initialized yet. + </para> + + <para> + When the chip-data is assigned to the card using + <function>snd_device_new()</function> with + <constant>SNDRV_DEV_LOWLELVEL</constant> , its destructor is + called at the last. That is, it is assured that all other + components like PCMs and controls have already been released. + You don't have to stop PCMs, etc. explicitly, but just + call low-level hardware stopping. + </para> + + <para> + The management of a memory-mapped region is almost as same as + the management of an I/O port. You'll need three fields like + the following: + + <informalexample> + <programlisting> +<![CDATA[ + struct mychip { + .... + unsigned long iobase_phys; + void __iomem *iobase_virt; + }; +]]> + </programlisting> + </informalexample> + + and the allocation would be like below: + + <informalexample> + <programlisting> +<![CDATA[ + if ((err = pci_request_regions(pci, "My Chip")) < 0) { + kfree(chip); + return err; + } + chip->iobase_phys = pci_resource_start(pci, 0); + chip->iobase_virt = ioremap_nocache(chip->iobase_phys, + pci_resource_len(pci, 0)); +]]> + </programlisting> + </informalexample> + + and the corresponding destructor would be: + + <informalexample> + <programlisting> +<![CDATA[ + static int snd_mychip_free(struct mychip *chip) + { + .... + if (chip->iobase_virt) + iounmap(chip->iobase_virt); + .... + pci_release_regions(chip->pci); + .... + } +]]> + </programlisting> + </informalexample> + </para> + + </section> + + <section id="pci-resource-device-struct"> + <title>Registration of Device Struct</title> + <para> + At some point, typically after calling <function>snd_device_new()</function>, + you need to register the struct <structname>device</structname> of the chip + you're handling for udev and co. ALSA provides a macro for compatibility with + older kernels. Simply call like the following: + <informalexample> + <programlisting> +<![CDATA[ + snd_card_set_dev(card, &pci->dev); +]]> + </programlisting> + </informalexample> + so that it stores the PCI's device pointer to the card. This will be + referred by ALSA core functions later when the devices are registered. + </para> + <para> + In the case of non-PCI, pass the proper device struct pointer of the BUS + instead. (In the case of legacy ISA without PnP, you don't have to do + anything.) + </para> + </section> + + <section id="pci-resource-entries"> + <title>PCI Entries</title> + <para> + So far, so good. Let's finish the missing PCI + stuff. At first, we need a + <structname>pci_device_id</structname> table for this + chipset. It's a table of PCI vendor/device ID number, and some + masks. + </para> + + <para> + For example, + + <informalexample> + <programlisting> +<![CDATA[ + static struct pci_device_id snd_mychip_ids[] = { + { PCI_VENDOR_ID_FOO, PCI_DEVICE_ID_BAR, + PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0, }, + .... + { 0, } + }; + MODULE_DEVICE_TABLE(pci, snd_mychip_ids); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The first and second fields of + the <structname>pci_device_id</structname> structure are the vendor and + device IDs. If you have no reason to filter the matching + devices, you can leave the remaining fields as above. The last + field of the <structname>pci_device_id</structname> struct contains + private data for this entry. You can specify any value here, for + example, to define specific operations for supported device IDs. + Such an example is found in the intel8x0 driver. + </para> + + <para> + The last entry of this list is the terminator. You must + specify this all-zero entry. + </para> + + <para> + Then, prepare the <structname>pci_driver</structname> record: + + <informalexample> + <programlisting> +<![CDATA[ + static struct pci_driver driver = { + .name = "My Own Chip", + .id_table = snd_mychip_ids, + .probe = snd_mychip_probe, + .remove = __devexit_p(snd_mychip_remove), + }; +]]> + </programlisting> + </informalexample> + </para> + + <para> + The <structfield>probe</structfield> and + <structfield>remove</structfield> functions have already + been defined in the previous sections. + The <structfield>remove</structfield> function should + be defined with the + <function>__devexit_p()</function> macro, so that it's not + defined for built-in (and non-hot-pluggable) case. The + <structfield>name</structfield> + field is the name string of this device. Note that you must not + use a slash <quote>/</quote> in this string. + </para> + + <para> + And at last, the module entries: + + <informalexample> + <programlisting> +<![CDATA[ + static int __init alsa_card_mychip_init(void) + { + return pci_register_driver(&driver); + } + + static void __exit alsa_card_mychip_exit(void) + { + pci_unregister_driver(&driver); + } + + module_init(alsa_card_mychip_init) + module_exit(alsa_card_mychip_exit) +]]> + </programlisting> + </informalexample> + </para> + + <para> + Note that these module entries are tagged with + <parameter>__init</parameter> and + <parameter>__exit</parameter> prefixes, not + <parameter>__devinit</parameter> nor + <parameter>__devexit</parameter>. + </para> + + <para> + Oh, one thing was forgotten. If you have no exported symbols, + you need to declare it in 2.2 or 2.4 kernels (it's not necessary in 2.6 kernels). + + <informalexample> + <programlisting> +<![CDATA[ + EXPORT_NO_SYMBOLS; +]]> + </programlisting> + </informalexample> + + That's all! + </para> + </section> + </chapter> + + +<!-- ****************************************************** --> +<!-- PCM Interface --> +<!-- ****************************************************** --> + <chapter id="pcm-interface"> + <title>PCM Interface</title> + + <section id="pcm-interface-general"> + <title>General</title> + <para> + The PCM middle layer of ALSA is quite powerful and it is only + necessary for each driver to implement the low-level functions + to access its hardware. + </para> + + <para> + For accessing to the PCM layer, you need to include + <filename><sound/pcm.h></filename> first. In addition, + <filename><sound/pcm_params.h></filename> might be needed + if you access to some functions related with hw_param. + </para> + + <para> + Each card device can have up to four pcm instances. A pcm + instance corresponds to a pcm device file. The limitation of + number of instances comes only from the available bit size of + the Linux's device numbers. Once when 64bit device number is + used, we'll have more pcm instances available. + </para> + + <para> + A pcm instance consists of pcm playback and capture streams, + and each pcm stream consists of one or more pcm substreams. Some + soundcards support multiple playback functions. For example, + emu10k1 has a PCM playback of 32 stereo substreams. In this case, at + each open, a free substream is (usually) automatically chosen + and opened. Meanwhile, when only one substream exists and it was + already opened, the successful open will either block + or error with <constant>EAGAIN</constant> according to the + file open mode. But you don't have to care about such details in your + driver. The PCM middle layer will take care of such work. + </para> + </section> + + <section id="pcm-interface-example"> + <title>Full Code Example</title> + <para> + The example code below does not include any hardware access + routines but shows only the skeleton, how to build up the PCM + interfaces. + + <example> + <title>PCM Example Code</title> + <programlisting> +<![CDATA[ + #include <sound/pcm.h> + .... + + /* hardware definition */ + static struct snd_pcm_hardware snd_mychip_playback_hw = { + .info = (SNDRV_PCM_INFO_MMAP | + SNDRV_PCM_INFO_INTERLEAVED | + SNDRV_PCM_INFO_BLOCK_TRANSFER | + SNDRV_PCM_INFO_MMAP_VALID), + .formats = SNDRV_PCM_FMTBIT_S16_LE, + .rates = SNDRV_PCM_RATE_8000_48000, + .rate_min = 8000, + .rate_max = 48000, + .channels_min = 2, + .channels_max = 2, + .buffer_bytes_max = 32768, + .period_bytes_min = 4096, + .period_bytes_max = 32768, + .periods_min = 1, + .periods_max = 1024, + }; + + /* hardware definition */ + static struct snd_pcm_hardware snd_mychip_capture_hw = { + .info = (SNDRV_PCM_INFO_MMAP | + SNDRV_PCM_INFO_INTERLEAVED | + SNDRV_PCM_INFO_BLOCK_TRANSFER | + SNDRV_PCM_INFO_MMAP_VALID), + .formats = SNDRV_PCM_FMTBIT_S16_LE, + .rates = SNDRV_PCM_RATE_8000_48000, + .rate_min = 8000, + .rate_max = 48000, + .channels_min = 2, + .channels_max = 2, + .buffer_bytes_max = 32768, + .period_bytes_min = 4096, + .period_bytes_max = 32768, + .periods_min = 1, + .periods_max = 1024, + }; + + /* open callback */ + static int snd_mychip_playback_open(struct snd_pcm_substream *substream) + { + struct mychip *chip = snd_pcm_substream_chip(substream); + struct snd_pcm_runtime *runtime = substream->runtime; + + runtime->hw = snd_mychip_playback_hw; + /* more hardware-initialization will be done here */ + .... + return 0; + } + + /* close callback */ + static int snd_mychip_playback_close(struct snd_pcm_substream *substream) + { + struct mychip *chip = snd_pcm_substream_chip(substream); + /* the hardware-specific codes will be here */ + .... + return 0; + + } + + /* open callback */ + static int snd_mychip_capture_open(struct snd_pcm_substream *substream) + { + struct mychip *chip = snd_pcm_substream_chip(substream); + struct snd_pcm_runtime *runtime = substream->runtime; + + runtime->hw = snd_mychip_capture_hw; + /* more hardware-initialization will be done here */ + .... + return 0; + } + + /* close callback */ + static int snd_mychip_capture_close(struct snd_pcm_substream *substream) + { + struct mychip *chip = snd_pcm_substream_chip(substream); + /* the hardware-specific codes will be here */ + .... + return 0; + + } + + /* hw_params callback */ + static int snd_mychip_pcm_hw_params(struct snd_pcm_substream *substream, + struct snd_pcm_hw_params *hw_params) + { + return snd_pcm_lib_malloc_pages(substream, + params_buffer_bytes(hw_params)); + } + + /* hw_free callback */ + static int snd_mychip_pcm_hw_free(struct snd_pcm_substream *substream) + { + return snd_pcm_lib_free_pages(substream); + } + + /* prepare callback */ + static int snd_mychip_pcm_prepare(struct snd_pcm_substream *substream) + { + struct mychip *chip = snd_pcm_substream_chip(substream); + struct snd_pcm_runtime *runtime = substream->runtime; + + /* set up the hardware with the current configuration + * for example... + */ + mychip_set_sample_format(chip, runtime->format); + mychip_set_sample_rate(chip, runtime->rate); + mychip_set_channels(chip, runtime->channels); + mychip_set_dma_setup(chip, runtime->dma_addr, + chip->buffer_size, + chip->period_size); + return 0; + } + + /* trigger callback */ + static int snd_mychip_pcm_trigger(struct snd_pcm_substream *substream, + int cmd) + { + switch (cmd) { + case SNDRV_PCM_TRIGGER_START: + /* do something to start the PCM engine */ + .... + break; + case SNDRV_PCM_TRIGGER_STOP: + /* do something to stop the PCM engine */ + .... + break; + default: + return -EINVAL; + } + } + + /* pointer callback */ + static snd_pcm_uframes_t + snd_mychip_pcm_pointer(struct snd_pcm_substream *substream) + { + struct mychip *chip = snd_pcm_substream_chip(substream); + unsigned int current_ptr; + + /* get the current hardware pointer */ + current_ptr = mychip_get_hw_pointer(chip); + return current_ptr; + } + + /* operators */ + static struct snd_pcm_ops snd_mychip_playback_ops = { + .open = snd_mychip_playback_open, + .close = snd_mychip_playback_close, + .ioctl = snd_pcm_lib_ioctl, + .hw_params = snd_mychip_pcm_hw_params, + .hw_free = snd_mychip_pcm_hw_free, + .prepare = snd_mychip_pcm_prepare, + .trigger = snd_mychip_pcm_trigger, + .pointer = snd_mychip_pcm_pointer, + }; + + /* operators */ + static struct snd_pcm_ops snd_mychip_capture_ops = { + .open = snd_mychip_capture_open, + .close = snd_mychip_capture_close, + .ioctl = snd_pcm_lib_ioctl, + .hw_params = snd_mychip_pcm_hw_params, + .hw_free = snd_mychip_pcm_hw_free, + .prepare = snd_mychip_pcm_prepare, + .trigger = snd_mychip_pcm_trigger, + .pointer = snd_mychip_pcm_pointer, + }; + + /* + * definitions of capture are omitted here... + */ + + /* create a pcm device */ + static int __devinit snd_mychip_new_pcm(struct mychip *chip) + { + struct snd_pcm *pcm; + int err; + + err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm); + if (err < 0) + return err; + pcm->private_data = chip; + strcpy(pcm->name, "My Chip"); + chip->pcm = pcm; + /* set operators */ + snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, + &snd_mychip_playback_ops); + snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, + &snd_mychip_capture_ops); + /* pre-allocation of buffers */ + /* NOTE: this may fail */ + snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, + snd_dma_pci_data(chip->pci), + 64*1024, 64*1024); + return 0; + } +]]> + </programlisting> + </example> + </para> + </section> + + <section id="pcm-interface-constructor"> + <title>Constructor</title> + <para> + A pcm instance is allocated by the <function>snd_pcm_new()</function> + function. It would be better to create a constructor for pcm, + namely, + + <informalexample> + <programlisting> +<![CDATA[ + static int __devinit snd_mychip_new_pcm(struct mychip *chip) + { + struct snd_pcm *pcm; + int err; + + err = snd_pcm_new(chip->card, "My Chip", 0, 1, 1, &pcm); + if (err < 0) + return err; + pcm->private_data = chip; + strcpy(pcm->name, "My Chip"); + chip->pcm = pcm; + .... + return 0; + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + The <function>snd_pcm_new()</function> function takes four + arguments. The first argument is the card pointer to which this + pcm is assigned, and the second is the ID string. + </para> + + <para> + The third argument (<parameter>index</parameter>, 0 in the + above) is the index of this new pcm. It begins from zero. If + you create more than one pcm instances, specify the + different numbers in this argument. For example, + <parameter>index</parameter> = 1 for the second PCM device. + </para> + + <para> + The fourth and fifth arguments are the number of substreams + for playback and capture, respectively. Here 1 is used for + both arguments. When no playback or capture substreams are available, + pass 0 to the corresponding argument. + </para> + + <para> + If a chip supports multiple playbacks or captures, you can + specify more numbers, but they must be handled properly in + open/close, etc. callbacks. When you need to know which + substream you are referring to, then it can be obtained from + struct <structname>snd_pcm_substream</structname> data passed to each callback + as follows: + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_pcm_substream *substream; + int index = substream->number; +]]> + </programlisting> + </informalexample> + </para> + + <para> + After the pcm is created, you need to set operators for each + pcm stream. + + <informalexample> + <programlisting> +<![CDATA[ + snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, + &snd_mychip_playback_ops); + snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, + &snd_mychip_capture_ops); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The operators are defined typically like this: + + <informalexample> + <programlisting> +<![CDATA[ + static struct snd_pcm_ops snd_mychip_playback_ops = { + .open = snd_mychip_pcm_open, + .close = snd_mychip_pcm_close, + .ioctl = snd_pcm_lib_ioctl, + .hw_params = snd_mychip_pcm_hw_params, + .hw_free = snd_mychip_pcm_hw_free, + .prepare = snd_mychip_pcm_prepare, + .trigger = snd_mychip_pcm_trigger, + .pointer = snd_mychip_pcm_pointer, + }; +]]> + </programlisting> + </informalexample> + + All the callbacks are described in the + <link linkend="pcm-interface-operators"><citetitle> + Operators</citetitle></link> subsection. + </para> + + <para> + After setting the operators, you probably will want to + pre-allocate the buffer. For the pre-allocation, simply call + the following: + + <informalexample> + <programlisting> +<![CDATA[ + snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, + snd_dma_pci_data(chip->pci), + 64*1024, 64*1024); +]]> + </programlisting> + </informalexample> + + It will allocate a buffer up to 64kB as default. + Buffer management details will be described in the later section <link + linkend="buffer-and-memory"><citetitle>Buffer and Memory + Management</citetitle></link>. + </para> + + <para> + Additionally, you can set some extra information for this pcm + in pcm->info_flags. + The available values are defined as + <constant>SNDRV_PCM_INFO_XXX</constant> in + <filename><sound/asound.h></filename>, which is used for + the hardware definition (described later). When your soundchip + supports only half-duplex, specify like this: + + <informalexample> + <programlisting> +<![CDATA[ + pcm->info_flags = SNDRV_PCM_INFO_HALF_DUPLEX; +]]> + </programlisting> + </informalexample> + </para> + </section> + + <section id="pcm-interface-destructor"> + <title>... And the Destructor?</title> + <para> + The destructor for a pcm instance is not always + necessary. Since the pcm device will be released by the middle + layer code automatically, you don't have to call the destructor + explicitly. + </para> + + <para> + The destructor would be necessary if you created + special records internally and needed to release them. In such a + case, set the destructor function to + pcm->private_free: + + <example> + <title>PCM Instance with a Destructor</title> + <programlisting> +<![CDATA[ + static void mychip_pcm_free(struct snd_pcm *pcm) + { + struct mychip *chip = snd_pcm_chip(pcm); + /* free your own data */ + kfree(chip->my_private_pcm_data); + /* do what you like else */ + .... + } + + static int __devinit snd_mychip_new_pcm(struct mychip *chip) + { + struct snd_pcm *pcm; + .... + /* allocate your own data */ + chip->my_private_pcm_data = kmalloc(...); + /* set the destructor */ + pcm->private_data = chip; + pcm->private_free = mychip_pcm_free; + .... + } +]]> + </programlisting> + </example> + </para> + </section> + + <section id="pcm-interface-runtime"> + <title>Runtime Pointer - The Chest of PCM Information</title> + <para> + When the PCM substream is opened, a PCM runtime instance is + allocated and assigned to the substream. This pointer is + accessible via <constant>substream->runtime</constant>. + This runtime pointer holds most information you need + to control the PCM: the copy of hw_params and sw_params configurations, the buffer + pointers, mmap records, spinlocks, etc. + </para> + + <para> + The definition of runtime instance is found in + <filename><sound/pcm.h></filename>. Here are + the contents of this file: + <informalexample> + <programlisting> +<![CDATA[ +struct _snd_pcm_runtime { + /* -- Status -- */ + struct snd_pcm_substream *trigger_master; + snd_timestamp_t trigger_tstamp; /* trigger timestamp */ + int overrange; + snd_pcm_uframes_t avail_max; + snd_pcm_uframes_t hw_ptr_base; /* Position at buffer restart */ + snd_pcm_uframes_t hw_ptr_interrupt; /* Position at interrupt time*/ + + /* -- HW params -- */ + snd_pcm_access_t access; /* access mode */ + snd_pcm_format_t format; /* SNDRV_PCM_FORMAT_* */ + snd_pcm_subformat_t subformat; /* subformat */ + unsigned int rate; /* rate in Hz */ + unsigned int channels; /* channels */ + snd_pcm_uframes_t period_size; /* period size */ + unsigned int periods; /* periods */ + snd_pcm_uframes_t buffer_size; /* buffer size */ + unsigned int tick_time; /* tick time */ + snd_pcm_uframes_t min_align; /* Min alignment for the format */ + size_t byte_align; + unsigned int frame_bits; + unsigned int sample_bits; + unsigned int info; + unsigned int rate_num; + unsigned int rate_den; + + /* -- SW params -- */ + struct timespec tstamp_mode; /* mmap timestamp is updated */ + unsigned int period_step; + unsigned int sleep_min; /* min ticks to sleep */ + snd_pcm_uframes_t start_threshold; + snd_pcm_uframes_t stop_threshold; + snd_pcm_uframes_t silence_threshold; /* Silence filling happens when + noise is nearest than this */ + snd_pcm_uframes_t silence_size; /* Silence filling size */ + snd_pcm_uframes_t boundary; /* pointers wrap point */ + + snd_pcm_uframes_t silenced_start; + snd_pcm_uframes_t silenced_size; + + snd_pcm_sync_id_t sync; /* hardware synchronization ID */ + + /* -- mmap -- */ + volatile struct snd_pcm_mmap_status *status; + volatile struct snd_pcm_mmap_control *control; + atomic_t mmap_count; + + /* -- locking / scheduling -- */ + spinlock_t lock; + wait_queue_head_t sleep; + struct timer_list tick_timer; + struct fasync_struct *fasync; + + /* -- private section -- */ + void *private_data; + void (*private_free)(struct snd_pcm_runtime *runtime); + + /* -- hardware description -- */ + struct snd_pcm_hardware hw; + struct snd_pcm_hw_constraints hw_constraints; + + /* -- interrupt callbacks -- */ + void (*transfer_ack_begin)(struct snd_pcm_substream *substream); + void (*transfer_ack_end)(struct snd_pcm_substream *substream); + + /* -- timer -- */ + unsigned int timer_resolution; /* timer resolution */ + + /* -- DMA -- */ + unsigned char *dma_area; /* DMA area */ + dma_addr_t dma_addr; /* physical bus address (not accessible from main CPU) */ + size_t dma_bytes; /* size of DMA area */ + + struct snd_dma_buffer *dma_buffer_p; /* allocated buffer */ + +#if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE) + /* -- OSS things -- */ + struct snd_pcm_oss_runtime oss; +#endif +}; +]]> + </programlisting> + </informalexample> + </para> + + <para> + For the operators (callbacks) of each sound driver, most of + these records are supposed to be read-only. Only the PCM + middle-layer changes / updates them. The exceptions are + the hardware description (hw), interrupt callbacks + (transfer_ack_xxx), DMA buffer information, and the private + data. Besides, if you use the standard buffer allocation + method via <function>snd_pcm_lib_malloc_pages()</function>, + you don't need to set the DMA buffer information by yourself. + </para> + + <para> + In the sections below, important records are explained. + </para> + + <section id="pcm-interface-runtime-hw"> + <title>Hardware Description</title> + <para> + The hardware descriptor (struct <structname>snd_pcm_hardware</structname>) + contains the definitions of the fundamental hardware + configuration. Above all, you'll need to define this in + <link linkend="pcm-interface-operators-open-callback"><citetitle> + the open callback</citetitle></link>. + Note that the runtime instance holds the copy of the + descriptor, not the pointer to the existing descriptor. That + is, in the open callback, you can modify the copied descriptor + (<constant>runtime->hw</constant>) as you need. For example, if the maximum + number of channels is 1 only on some chip models, you can + still use the same hardware descriptor and change the + channels_max later: + <informalexample> + <programlisting> +<![CDATA[ + struct snd_pcm_runtime *runtime = substream->runtime; + ... + runtime->hw = snd_mychip_playback_hw; /* common definition */ + if (chip->model == VERY_OLD_ONE) + runtime->hw.channels_max = 1; +]]> + </programlisting> + </informalexample> + </para> + + <para> + Typically, you'll have a hardware descriptor as below: + <informalexample> + <programlisting> +<![CDATA[ + static struct snd_pcm_hardware snd_mychip_playback_hw = { + .info = (SNDRV_PCM_INFO_MMAP | + SNDRV_PCM_INFO_INTERLEAVED | + SNDRV_PCM_INFO_BLOCK_TRANSFER | + SNDRV_PCM_INFO_MMAP_VALID), + .formats = SNDRV_PCM_FMTBIT_S16_LE, + .rates = SNDRV_PCM_RATE_8000_48000, + .rate_min = 8000, + .rate_max = 48000, + .channels_min = 2, + .channels_max = 2, + .buffer_bytes_max = 32768, + .period_bytes_min = 4096, + .period_bytes_max = 32768, + .periods_min = 1, + .periods_max = 1024, + }; +]]> + </programlisting> + </informalexample> + </para> + + <para> + <itemizedlist> + <listitem><para> + The <structfield>info</structfield> field contains the type and + capabilities of this pcm. The bit flags are defined in + <filename><sound/asound.h></filename> as + <constant>SNDRV_PCM_INFO_XXX</constant>. Here, at least, you + have to specify whether the mmap is supported and which + interleaved format is supported. + When the is supported, add the + <constant>SNDRV_PCM_INFO_MMAP</constant> flag here. When the + hardware supports the interleaved or the non-interleaved + formats, <constant>SNDRV_PCM_INFO_INTERLEAVED</constant> or + <constant>SNDRV_PCM_INFO_NONINTERLEAVED</constant> flag must + be set, respectively. If both are supported, you can set both, + too. + </para> + + <para> + In the above example, <constant>MMAP_VALID</constant> and + <constant>BLOCK_TRANSFER</constant> are specified for the OSS mmap + mode. Usually both are set. Of course, + <constant>MMAP_VALID</constant> is set only if the mmap is + really supported. + </para> + + <para> + The other possible flags are + <constant>SNDRV_PCM_INFO_PAUSE</constant> and + <constant>SNDRV_PCM_INFO_RESUME</constant>. The + <constant>PAUSE</constant> bit means that the pcm supports the + <quote>pause</quote> operation, while the + <constant>RESUME</constant> bit means that the pcm supports + the full <quote>suspend/resume</quote> operation. + If the <constant>PAUSE</constant> flag is set, + the <structfield>trigger</structfield> callback below + must handle the corresponding (pause push/release) commands. + The suspend/resume trigger commands can be defined even without + the <constant>RESUME</constant> flag. See <link + linkend="power-management"><citetitle> + Power Management</citetitle></link> section for details. + </para> + + <para> + When the PCM substreams can be synchronized (typically, + synchronized start/stop of a playback and a capture streams), + you can give <constant>SNDRV_PCM_INFO_SYNC_START</constant>, + too. In this case, you'll need to check the linked-list of + PCM substreams in the trigger callback. This will be + described in the later section. + </para> + </listitem> + + <listitem> + <para> + <structfield>formats</structfield> field contains the bit-flags + of supported formats (<constant>SNDRV_PCM_FMTBIT_XXX</constant>). + If the hardware supports more than one format, give all or'ed + bits. In the example above, the signed 16bit little-endian + format is specified. + </para> + </listitem> + + <listitem> + <para> + <structfield>rates</structfield> field contains the bit-flags of + supported rates (<constant>SNDRV_PCM_RATE_XXX</constant>). + When the chip supports continuous rates, pass + <constant>CONTINUOUS</constant> bit additionally. + The pre-defined rate bits are provided only for typical + rates. If your chip supports unconventional rates, you need to add + the <constant>KNOT</constant> bit and set up the hardware + constraint manually (explained later). + </para> + </listitem> + + <listitem> + <para> + <structfield>rate_min</structfield> and + <structfield>rate_max</structfield> define the minimum and + maximum sample rate. This should correspond somehow to + <structfield>rates</structfield> bits. + </para> + </listitem> + + <listitem> + <para> + <structfield>channel_min</structfield> and + <structfield>channel_max</structfield> + define, as you might already expected, the minimum and maximum + number of channels. + </para> + </listitem> + + <listitem> + <para> + <structfield>buffer_bytes_max</structfield> defines the + maximum buffer size in bytes. There is no + <structfield>buffer_bytes_min</structfield> field, since + it can be calculated from the minimum period size and the + minimum number of periods. + Meanwhile, <structfield>period_bytes_min</structfield> and + define the minimum and maximum size of the period in bytes. + <structfield>periods_max</structfield> and + <structfield>periods_min</structfield> define the maximum and + minimum number of periods in the buffer. + </para> + + <para> + The <quote>period</quote> is a term that corresponds to + a fragment in the OSS world. The period defines the size at + which a PCM interrupt is generated. This size strongly + depends on the hardware. + Generally, the smaller period size will give you more + interrupts, that is, more controls. + In the case of capture, this size defines the input latency. + On the other hand, the whole buffer size defines the + output latency for the playback direction. + </para> + </listitem> + + <listitem> + <para> + There is also a field <structfield>fifo_size</structfield>. + This specifies the size of the hardware FIFO, but currently it + is neither used in the driver nor in the alsa-lib. So, you + can ignore this field. + </para> + </listitem> + </itemizedlist> + </para> + </section> + + <section id="pcm-interface-runtime-config"> + <title>PCM Configurations</title> + <para> + Ok, let's go back again to the PCM runtime records. + The most frequently referred records in the runtime instance are + the PCM configurations. + The PCM configurations are stored in the runtime instance + after the application sends <type>hw_params</type> data via + alsa-lib. There are many fields copied from hw_params and + sw_params structs. For example, + <structfield>format</structfield> holds the format type + chosen by the application. This field contains the enum value + <constant>SNDRV_PCM_FORMAT_XXX</constant>. + </para> + + <para> + One thing to be noted is that the configured buffer and period + sizes are stored in <quote>frames</quote> in the runtime. + In the ALSA world, 1 frame = channels * samples-size. + For conversion between frames and bytes, you can use the + <function>frames_to_bytes()</function> and + <function>bytes_to_frames()</function> helper functions. + <informalexample> + <programlisting> +<![CDATA[ + period_bytes = frames_to_bytes(runtime, runtime->period_size); +]]> + </programlisting> + </informalexample> + </para> + + <para> + Also, many software parameters (sw_params) are + stored in frames, too. Please check the type of the field. + <type>snd_pcm_uframes_t</type> is for the frames as unsigned + integer while <type>snd_pcm_sframes_t</type> is for the frames + as signed integer. + </para> + </section> + + <section id="pcm-interface-runtime-dma"> + <title>DMA Buffer Information</title> + <para> + The DMA buffer is defined by the following four fields, + <structfield>dma_area</structfield>, + <structfield>dma_addr</structfield>, + <structfield>dma_bytes</structfield> and + <structfield>dma_private</structfield>. + The <structfield>dma_area</structfield> holds the buffer + pointer (the logical address). You can call + <function>memcpy</function> from/to + this pointer. Meanwhile, <structfield>dma_addr</structfield> + holds the physical address of the buffer. This field is + specified only when the buffer is a linear buffer. + <structfield>dma_bytes</structfield> holds the size of buffer + in bytes. <structfield>dma_private</structfield> is used for + the ALSA DMA allocator. + </para> + + <para> + If you use a standard ALSA function, + <function>snd_pcm_lib_malloc_pages()</function>, for + allocating the buffer, these fields are set by the ALSA middle + layer, and you should <emphasis>not</emphasis> change them by + yourself. You can read them but not write them. + On the other hand, if you want to allocate the buffer by + yourself, you'll need to manage it in hw_params callback. + At least, <structfield>dma_bytes</structfield> is mandatory. + <structfield>dma_area</structfield> is necessary when the + buffer is mmapped. If your driver doesn't support mmap, this + field is not necessary. <structfield>dma_addr</structfield> + is also optional. You can use + <structfield>dma_private</structfield> as you like, too. + </para> + </section> + + <section id="pcm-interface-runtime-status"> + <title>Running Status</title> + <para> + The running status can be referred via <constant>runtime->status</constant>. + This is the pointer to the struct <structname>snd_pcm_mmap_status</structname> + record. For example, you can get the current DMA hardware + pointer via <constant>runtime->status->hw_ptr</constant>. + </para> + + <para> + The DMA application pointer can be referred via + <constant>runtime->control</constant>, which points to the + struct <structname>snd_pcm_mmap_control</structname> record. + However, accessing directly to this value is not recommended. + </para> + </section> + + <section id="pcm-interface-runtime-private"> + <title>Private Data</title> + <para> + You can allocate a record for the substream and store it in + <constant>runtime->private_data</constant>. Usually, this + is done in + <link linkend="pcm-interface-operators-open-callback"><citetitle> + the open callback</citetitle></link>. + Don't mix this with <constant>pcm->private_data</constant>. + The <constant>pcm->private_data</constant> usually points to the + chip instance assigned statically at the creation of PCM, while the + <constant>runtime->private_data</constant> points to a dynamic + data structure created at the PCM open callback. + + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_open(struct snd_pcm_substream *substream) + { + struct my_pcm_data *data; + .... + data = kmalloc(sizeof(*data), GFP_KERNEL); + substream->runtime->private_data = data; + .... + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + The allocated object must be released in + <link linkend="pcm-interface-operators-open-callback"><citetitle> + the close callback</citetitle></link>. + </para> + </section> + + <section id="pcm-interface-runtime-intr"> + <title>Interrupt Callbacks</title> + <para> + The field <structfield>transfer_ack_begin</structfield> and + <structfield>transfer_ack_end</structfield> are called at + the beginning and at the end of + <function>snd_pcm_period_elapsed()</function>, respectively. + </para> + </section> + + </section> + + <section id="pcm-interface-operators"> + <title>Operators</title> + <para> + OK, now let me give details about each pcm callback + (<parameter>ops</parameter>). In general, every callback must + return 0 if successful, or a negative error number + such as <constant>-EINVAL</constant>. To choose an appropriate + error number, it is advised to check what value other parts of + the kernel return when the same kind of request fails. + </para> + + <para> + The callback function takes at least the argument with + <structname>snd_pcm_substream</structname> pointer. To retrieve + the chip record from the given substream instance, you can use the + following macro. + + <informalexample> + <programlisting> +<![CDATA[ + int xxx() { + struct mychip *chip = snd_pcm_substream_chip(substream); + .... + } +]]> + </programlisting> + </informalexample> + + The macro reads <constant>substream->private_data</constant>, + which is a copy of <constant>pcm->private_data</constant>. + You can override the former if you need to assign different data + records per PCM substream. For example, the cmi8330 driver assigns + different private_data for playback and capture directions, + because it uses two different codecs (SB- and AD-compatible) for + different directions. + </para> + + <section id="pcm-interface-operators-open-callback"> + <title>open callback</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_open(struct snd_pcm_substream *substream); +]]> + </programlisting> + </informalexample> + + This is called when a pcm substream is opened. + </para> + + <para> + At least, here you have to initialize the runtime->hw + record. Typically, this is done by like this: + + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_open(struct snd_pcm_substream *substream) + { + struct mychip *chip = snd_pcm_substream_chip(substream); + struct snd_pcm_runtime *runtime = substream->runtime; + + runtime->hw = snd_mychip_playback_hw; + return 0; + } +]]> + </programlisting> + </informalexample> + + where <parameter>snd_mychip_playback_hw</parameter> is the + pre-defined hardware description. + </para> + + <para> + You can allocate a private data in this callback, as described + in <link linkend="pcm-interface-runtime-private"><citetitle> + Private Data</citetitle></link> section. + </para> + + <para> + If the hardware configuration needs more constraints, set the + hardware constraints here, too. + See <link linkend="pcm-interface-constraints"><citetitle> + Constraints</citetitle></link> for more details. + </para> + </section> + + <section id="pcm-interface-operators-close-callback"> + <title>close callback</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_close(struct snd_pcm_substream *substream); +]]> + </programlisting> + </informalexample> + + Obviously, this is called when a pcm substream is closed. + </para> + + <para> + Any private instance for a pcm substream allocated in the + open callback will be released here. + + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_close(struct snd_pcm_substream *substream) + { + .... + kfree(substream->runtime->private_data); + .... + } +]]> + </programlisting> + </informalexample> + </para> + </section> + + <section id="pcm-interface-operators-ioctl-callback"> + <title>ioctl callback</title> + <para> + This is used for any special call to pcm ioctls. But + usually you can pass a generic ioctl callback, + <function>snd_pcm_lib_ioctl</function>. + </para> + </section> + + <section id="pcm-interface-operators-hw-params-callback"> + <title>hw_params callback</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_hw_params(struct snd_pcm_substream *substream, + struct snd_pcm_hw_params *hw_params); +]]> + </programlisting> + </informalexample> + </para> + + <para> + This is called when the hardware parameter + (<structfield>hw_params</structfield>) is set + up by the application, + that is, once when the buffer size, the period size, the + format, etc. are defined for the pcm substream. + </para> + + <para> + Many hardware setups should be done in this callback, + including the allocation of buffers. + </para> + + <para> + Parameters to be initialized are retrieved by + <function>params_xxx()</function> macros. To allocate + buffer, you can call a helper function, + + <informalexample> + <programlisting> +<![CDATA[ + snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(hw_params)); +]]> + </programlisting> + </informalexample> + + <function>snd_pcm_lib_malloc_pages()</function> is available + only when the DMA buffers have been pre-allocated. + See the section <link + linkend="buffer-and-memory-buffer-types"><citetitle> + Buffer Types</citetitle></link> for more details. + </para> + + <para> + Note that this and <structfield>prepare</structfield> callbacks + may be called multiple times per initialization. + For example, the OSS emulation may + call these callbacks at each change via its ioctl. + </para> + + <para> + Thus, you need to be careful not to allocate the same buffers + many times, which will lead to memory leaks! Calling the + helper function above many times is OK. It will release the + previous buffer automatically when it was already allocated. + </para> + + <para> + Another note is that this callback is non-atomic + (schedulable). This is important, because the + <structfield>trigger</structfield> callback + is atomic (non-schedulable). That is, mutexes or any + schedule-related functions are not available in + <structfield>trigger</structfield> callback. + Please see the subsection + <link linkend="pcm-interface-atomicity"><citetitle> + Atomicity</citetitle></link> for details. + </para> + </section> + + <section id="pcm-interface-operators-hw-free-callback"> + <title>hw_free callback</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_hw_free(struct snd_pcm_substream *substream); +]]> + </programlisting> + </informalexample> + </para> + + <para> + This is called to release the resources allocated via + <structfield>hw_params</structfield>. For example, releasing the + buffer via + <function>snd_pcm_lib_malloc_pages()</function> is done by + calling the following: + + <informalexample> + <programlisting> +<![CDATA[ + snd_pcm_lib_free_pages(substream); +]]> + </programlisting> + </informalexample> + </para> + + <para> + This function is always called before the close callback is called. + Also, the callback may be called multiple times, too. + Keep track whether the resource was already released. + </para> + </section> + + <section id="pcm-interface-operators-prepare-callback"> + <title>prepare callback</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_prepare(struct snd_pcm_substream *substream); +]]> + </programlisting> + </informalexample> + </para> + + <para> + This callback is called when the pcm is + <quote>prepared</quote>. You can set the format type, sample + rate, etc. here. The difference from + <structfield>hw_params</structfield> is that the + <structfield>prepare</structfield> callback will be called each + time + <function>snd_pcm_prepare()</function> is called, i.e. when + recovering after underruns, etc. + </para> + + <para> + Note that this callback is now non-atomic. + You can use schedule-related functions safely in this callback. + </para> + + <para> + In this and the following callbacks, you can refer to the + values via the runtime record, + substream->runtime. + For example, to get the current + rate, format or channels, access to + runtime->rate, + runtime->format or + runtime->channels, respectively. + The physical address of the allocated buffer is set to + runtime->dma_area. The buffer and period sizes are + in runtime->buffer_size and runtime->period_size, + respectively. + </para> + + <para> + Be careful that this callback will be called many times at + each setup, too. + </para> + </section> + + <section id="pcm-interface-operators-trigger-callback"> + <title>trigger callback</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_trigger(struct snd_pcm_substream *substream, int cmd); +]]> + </programlisting> + </informalexample> + + This is called when the pcm is started, stopped or paused. + </para> + + <para> + Which action is specified in the second argument, + <constant>SNDRV_PCM_TRIGGER_XXX</constant> in + <filename><sound/pcm.h></filename>. At least, + the <constant>START</constant> and <constant>STOP</constant> + commands must be defined in this callback. + + <informalexample> + <programlisting> +<![CDATA[ + switch (cmd) { + case SNDRV_PCM_TRIGGER_START: + /* do something to start the PCM engine */ + break; + case SNDRV_PCM_TRIGGER_STOP: + /* do something to stop the PCM engine */ + break; + default: + return -EINVAL; + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + When the pcm supports the pause operation (given in the info + field of the hardware table), the <constant>PAUSE_PUSE</constant> + and <constant>PAUSE_RELEASE</constant> commands must be + handled here, too. The former is the command to pause the pcm, + and the latter to restart the pcm again. + </para> + + <para> + When the pcm supports the suspend/resume operation, + regardless of full or partial suspend/resume support, + the <constant>SUSPEND</constant> and <constant>RESUME</constant> + commands must be handled, too. + These commands are issued when the power-management status is + changed. Obviously, the <constant>SUSPEND</constant> and + <constant>RESUME</constant> commands + suspend and resume the pcm substream, and usually, they + are identical to the <constant>STOP</constant> and + <constant>START</constant> commands, respectively. + See the <link linkend="power-management"><citetitle> + Power Management</citetitle></link> section for details. + </para> + + <para> + As mentioned, this callback is atomic. You cannot call + functions which may sleep. + The trigger callback should be as minimal as possible, + just really triggering the DMA. The other stuff should be + initialized hw_params and prepare callbacks properly + beforehand. + </para> + </section> + + <section id="pcm-interface-operators-pointer-callback"> + <title>pointer callback</title> + <para> + <informalexample> + <programlisting> +<![CDATA[ + static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream) +]]> + </programlisting> + </informalexample> + + This callback is called when the PCM middle layer inquires + the current hardware position on the buffer. The position must + be returned in frames, + ranging from 0 to buffer_size - 1. + </para> + + <para> + This is called usually from the buffer-update routine in the + pcm middle layer, which is invoked when + <function>snd_pcm_period_elapsed()</function> is called in the + interrupt routine. Then the pcm middle layer updates the + position and calculates the available space, and wakes up the + sleeping poll threads, etc. + </para> + + <para> + This callback is also atomic. + </para> + </section> + + <section id="pcm-interface-operators-copy-silence"> + <title>copy and silence callbacks</title> + <para> + These callbacks are not mandatory, and can be omitted in + most cases. These callbacks are used when the hardware buffer + cannot be in the normal memory space. Some chips have their + own buffer on the hardware which is not mappable. In such a + case, you have to transfer the data manually from the memory + buffer to the hardware buffer. Or, if the buffer is + non-contiguous on both physical and virtual memory spaces, + these callbacks must be defined, too. + </para> + + <para> + If these two callbacks are defined, copy and set-silence + operations are done by them. The detailed will be described in + the later section <link + linkend="buffer-and-memory"><citetitle>Buffer and Memory + Management</citetitle></link>. + </para> + </section> + + <section id="pcm-interface-operators-ack"> + <title>ack callback</title> + <para> + This callback is also not mandatory. This callback is called + when the appl_ptr is updated in read or write operations. + Some drivers like emu10k1-fx and cs46xx need to track the + current appl_ptr for the internal buffer, and this callback + is useful only for such a purpose. + </para> + <para> + This callback is atomic. + </para> + </section> + + <section id="pcm-interface-operators-page-callback"> + <title>page callback</title> + + <para> + This callback is optional too. This callback is used + mainly for non-contiguous buffers. The mmap calls this + callback to get the page address. Some examples will be + explained in the later section <link + linkend="buffer-and-memory"><citetitle>Buffer and Memory + Management</citetitle></link>, too. + </para> + </section> + </section> + + <section id="pcm-interface-interrupt-handler"> + <title>Interrupt Handler</title> + <para> + The rest of pcm stuff is the PCM interrupt handler. The + role of PCM interrupt handler in the sound driver is to update + the buffer position and to tell the PCM middle layer when the + buffer position goes across the prescribed period size. To + inform this, call the <function>snd_pcm_period_elapsed()</function> + function. + </para> + + <para> + There are several types of sound chips to generate the interrupts. + </para> + + <section id="pcm-interface-interrupt-handler-boundary"> + <title>Interrupts at the period (fragment) boundary</title> + <para> + This is the most frequently found type: the hardware + generates an interrupt at each period boundary. + In this case, you can call + <function>snd_pcm_period_elapsed()</function> at each + interrupt. + </para> + + <para> + <function>snd_pcm_period_elapsed()</function> takes the + substream pointer as its argument. Thus, you need to keep the + substream pointer accessible from the chip instance. For + example, define substream field in the chip record to hold the + current running substream pointer, and set the pointer value + at open callback (and reset at close callback). + </para> + + <para> + If you acquire a spinlock in the interrupt handler, and the + lock is used in other pcm callbacks, too, then you have to + release the lock before calling + <function>snd_pcm_period_elapsed()</function>, because + <function>snd_pcm_period_elapsed()</function> calls other pcm + callbacks inside. + </para> + + <para> + Typical code would be like: + + <example> + <title>Interrupt Handler Case #1</title> + <programlisting> +<![CDATA[ + static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) + { + struct mychip *chip = dev_id; + spin_lock(&chip->lock); + .... + if (pcm_irq_invoked(chip)) { + /* call updater, unlock before it */ + spin_unlock(&chip->lock); + snd_pcm_period_elapsed(chip->substream); + spin_lock(&chip->lock); + /* acknowledge the interrupt if necessary */ + } + .... + spin_unlock(&chip->lock); + return IRQ_HANDLED; + } +]]> + </programlisting> + </example> + </para> + </section> + + <section id="pcm-interface-interrupt-handler-timer"> + <title>High frequency timer interrupts</title> + <para> + This happense when the hardware doesn't generate interrupts + at the period boundary but issues timer interrupts at a fixed + timer rate (e.g. es1968 or ymfpci drivers). + In this case, you need to check the current hardware + position and accumulate the processed sample length at each + interrupt. When the accumulated size exceeds the period + size, call + <function>snd_pcm_period_elapsed()</function> and reset the + accumulator. + </para> + + <para> + Typical code would be like the following. + + <example> + <title>Interrupt Handler Case #2</title> + <programlisting> +<![CDATA[ + static irqreturn_t snd_mychip_interrupt(int irq, void *dev_id) + { + struct mychip *chip = dev_id; + spin_lock(&chip->lock); + .... + if (pcm_irq_invoked(chip)) { + unsigned int last_ptr, size; + /* get the current hardware pointer (in frames) */ + last_ptr = get_hw_ptr(chip); + /* calculate the processed frames since the + * last update + */ + if (last_ptr < chip->last_ptr) + size = runtime->buffer_size + last_ptr + - chip->last_ptr; + else + size = last_ptr - chip->last_ptr; + /* remember the last updated point */ + chip->last_ptr = last_ptr; + /* accumulate the size */ + chip->size += size; + /* over the period boundary? */ + if (chip->size >= runtime->period_size) { + /* reset the accumulator */ + chip->size %= runtime->period_size; + /* call updater */ + spin_unlock(&chip->lock); + snd_pcm_period_elapsed(substream); + spin_lock(&chip->lock); + } + /* acknowledge the interrupt if necessary */ + } + .... + spin_unlock(&chip->lock); + return IRQ_HANDLED; + } +]]> + </programlisting> + </example> + </para> + </section> + + <section id="pcm-interface-interrupt-handler-both"> + <title>On calling <function>snd_pcm_period_elapsed()</function></title> + <para> + In both cases, even if more than one period are elapsed, you + don't have to call + <function>snd_pcm_period_elapsed()</function> many times. Call + only once. And the pcm layer will check the current hardware + pointer and update to the latest status. + </para> + </section> + </section> + + <section id="pcm-interface-atomicity"> + <title>Atomicity</title> + <para> + One of the most important (and thus difficult to debug) problems + in kernel programming are race conditions. + In the Linux kernel, they are usually avoided via spin-locks, mutexes + or semaphores. In general, if a race condition can happen + in an interrupt handler, it has to be managed atomically, and you + have to use a spinlock to protect the critical session. If the + critical section is not in interrupt handler code and + if taking a relatively long time to execute is acceptable, you + should use mutexes or semaphores instead. + </para> + + <para> + As already seen, some pcm callbacks are atomic and some are + not. For example, the <parameter>hw_params</parameter> callback is + non-atomic, while <parameter>trigger</parameter> callback is + atomic. This means, the latter is called already in a spinlock + held by the PCM middle layer. Please take this atomicity into + account when you choose a locking scheme in the callbacks. + </para> + + <para> + In the atomic callbacks, you cannot use functions which may call + <function>schedule</function> or go to + <function>sleep</function>. Semaphores and mutexes can sleep, + and hence they cannot be used inside the atomic callbacks + (e.g. <parameter>trigger</parameter> callback). + To implement some delay in such a callback, please use + <function>udelay()</function> or <function>mdelay()</function>. + </para> + + <para> + All three atomic callbacks (trigger, pointer, and ack) are + called with local interrupts disabled. + </para> + + </section> + <section id="pcm-interface-constraints"> + <title>Constraints</title> + <para> + If your chip supports unconventional sample rates, or only the + limited samples, you need to set a constraint for the + condition. + </para> + + <para> + For example, in order to restrict the sample rates in the some + supported values, use + <function>snd_pcm_hw_constraint_list()</function>. + You need to call this function in the open callback. + + <example> + <title>Example of Hardware Constraints</title> + <programlisting> +<![CDATA[ + static unsigned int rates[] = + {4000, 10000, 22050, 44100}; + static struct snd_pcm_hw_constraint_list constraints_rates = { + .count = ARRAY_SIZE(rates), + .list = rates, + .mask = 0, + }; + + static int snd_mychip_pcm_open(struct snd_pcm_substream *substream) + { + int err; + .... + err = snd_pcm_hw_constraint_list(substream->runtime, 0, + SNDRV_PCM_HW_PARAM_RATE, + &constraints_rates); + if (err < 0) + return err; + .... + } +]]> + </programlisting> + </example> + </para> + + <para> + There are many different constraints. + Look at <filename>sound/pcm.h</filename> for a complete list. + You can even define your own constraint rules. + For example, let's suppose my_chip can manage a substream of 1 channel + if and only if the format is S16_LE, otherwise it supports any format + specified in the <structname>snd_pcm_hardware</structname> structure (or in any + other constraint_list). You can build a rule like this: + + <example> + <title>Example of Hardware Constraints for Channels</title> + <programlisting> +<![CDATA[ + static int hw_rule_format_by_channels(struct snd_pcm_hw_params *params, + struct snd_pcm_hw_rule *rule) + { + struct snd_interval *c = hw_param_interval(params, + SNDRV_PCM_HW_PARAM_CHANNELS); + struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); + struct snd_mask fmt; + + snd_mask_any(&fmt); /* Init the struct */ + if (c->min < 2) { + fmt.bits[0] &= SNDRV_PCM_FMTBIT_S16_LE; + return snd_mask_refine(f, &fmt); + } + return 0; + } +]]> + </programlisting> + </example> + </para> + + <para> + Then you need to call this function to add your rule: + + <informalexample> + <programlisting> +<![CDATA[ + snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS, + hw_rule_channels_by_format, 0, SNDRV_PCM_HW_PARAM_FORMAT, + -1); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The rule function is called when an application sets the number of + channels. But an application can set the format before the number of + channels. Thus you also need to define the inverse rule: + + <example> + <title>Example of Hardware Constraints for Channels</title> + <programlisting> +<![CDATA[ + static int hw_rule_channels_by_format(struct snd_pcm_hw_params *params, + struct snd_pcm_hw_rule *rule) + { + struct snd_interval *c = hw_param_interval(params, + SNDRV_PCM_HW_PARAM_CHANNELS); + struct snd_mask *f = hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); + struct snd_interval ch; + + snd_interval_any(&ch); + if (f->bits[0] == SNDRV_PCM_FMTBIT_S16_LE) { + ch.min = ch.max = 1; + ch.integer = 1; + return snd_interval_refine(c, &ch); + } + return 0; + } +]]> + </programlisting> + </example> + </para> + + <para> + ...and in the open callback: + <informalexample> + <programlisting> +<![CDATA[ + snd_pcm_hw_rule_add(substream->runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT, + hw_rule_format_by_channels, 0, SNDRV_PCM_HW_PARAM_CHANNELS, + -1); +]]> + </programlisting> + </informalexample> + </para> + + <para> + I won't give more details here, rather I + would like to say, <quote>Luke, use the source.</quote> + </para> + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- Control Interface --> +<!-- ****************************************************** --> + <chapter id="control-interface"> + <title>Control Interface</title> + + <section id="control-interface-general"> + <title>General</title> + <para> + The control interface is used widely for many switches, + sliders, etc. which are accessed from user-space. Its most + important use is the mixer interface. In other words, since ALSA + 0.9.x, all the mixer stuff is implemented on the control kernel API. + </para> + + <para> + ALSA has a well-defined AC97 control module. If your chip + supports only the AC97 and nothing else, you can skip this + section. + </para> + + <para> + The control API is defined in + <filename><sound/control.h></filename>. + Include this file if you want to add your own controls. + </para> + </section> + + <section id="control-interface-definition"> + <title>Definition of Controls</title> + <para> + To create a new control, you need to define the + following three + callbacks: <structfield>info</structfield>, + <structfield>get</structfield> and + <structfield>put</structfield>. Then, define a + struct <structname>snd_kcontrol_new</structname> record, such as: + + <example> + <title>Definition of a Control</title> + <programlisting> +<![CDATA[ + static struct snd_kcontrol_new my_control __devinitdata = { + .iface = SNDRV_CTL_ELEM_IFACE_MIXER, + .name = "PCM Playback Switch", + .index = 0, + .access = SNDRV_CTL_ELEM_ACCESS_READWRITE, + .private_value = 0xffff, + .info = my_control_info, + .get = my_control_get, + .put = my_control_put + }; +]]> + </programlisting> + </example> + </para> + + <para> + Most likely the control is created via + <function>snd_ctl_new1()</function>, and in such a case, you can + add the <parameter>__devinitdata</parameter> prefix to the + definition as above. + </para> + + <para> + The <structfield>iface</structfield> field specifies the control + type, <constant>SNDRV_CTL_ELEM_IFACE_XXX</constant>, which + is usually <constant>MIXER</constant>. + Use <constant>CARD</constant> for global controls that are not + logically part of the mixer. + If the control is closely associated with some specific device on + the sound card, use <constant>HWDEP</constant>, + <constant>PCM</constant>, <constant>RAWMIDI</constant>, + <constant>TIMER</constant>, or <constant>SEQUENCER</constant>, and + specify the device number with the + <structfield>device</structfield> and + <structfield>subdevice</structfield> fields. + </para> + + <para> + The <structfield>name</structfield> is the name identifier + string. Since ALSA 0.9.x, the control name is very important, + because its role is classified from its name. There are + pre-defined standard control names. The details are described in + the <link linkend="control-interface-control-names"><citetitle> + Control Names</citetitle></link> subsection. + </para> + + <para> + The <structfield>index</structfield> field holds the index number + of this control. If there are several different controls with + the same name, they can be distinguished by the index + number. This is the case when + several codecs exist on the card. If the index is zero, you can + omit the definition above. + </para> + + <para> + The <structfield>access</structfield> field contains the access + type of this control. Give the combination of bit masks, + <constant>SNDRV_CTL_ELEM_ACCESS_XXX</constant>, there. + The details will be explained in + the <link linkend="control-interface-access-flags"><citetitle> + Access Flags</citetitle></link> subsection. + </para> + + <para> + The <structfield>private_value</structfield> field contains + an arbitrary long integer value for this record. When using + the generic <structfield>info</structfield>, + <structfield>get</structfield> and + <structfield>put</structfield> callbacks, you can pass a value + through this field. If several small numbers are necessary, you can + combine them in bitwise. Or, it's possible to give a pointer + (casted to unsigned long) of some record to this field, too. + </para> + + <para> + The <structfield>tlv</structfield> field can be used to provide + metadata about the control; see the + <link linkend="control-interface-tlv"> + <citetitle>Metadata</citetitle></link> subsection. + </para> + + <para> + The other three are + <link linkend="control-interface-callbacks"><citetitle> + callback functions</citetitle></link>. + </para> + </section> + + <section id="control-interface-control-names"> + <title>Control Names</title> + <para> + There are some standards to define the control names. A + control is usually defined from the three parts as + <quote>SOURCE DIRECTION FUNCTION</quote>. + </para> + + <para> + The first, <constant>SOURCE</constant>, specifies the source + of the control, and is a string such as <quote>Master</quote>, + <quote>PCM</quote>, <quote>CD</quote> and + <quote>Line</quote>. There are many pre-defined sources. + </para> + + <para> + The second, <constant>DIRECTION</constant>, is one of the + following strings according to the direction of the control: + <quote>Playback</quote>, <quote>Capture</quote>, <quote>Bypass + Playback</quote> and <quote>Bypass Capture</quote>. Or, it can + be omitted, meaning both playback and capture directions. + </para> + + <para> + The third, <constant>FUNCTION</constant>, is one of the + following strings according to the function of the control: + <quote>Switch</quote>, <quote>Volume</quote> and + <quote>Route</quote>. + </para> + + <para> + The example of control names are, thus, <quote>Master Capture + Switch</quote> or <quote>PCM Playback Volume</quote>. + </para> + + <para> + There are some exceptions: + </para> + + <section id="control-interface-control-names-global"> + <title>Global capture and playback</title> + <para> + <quote>Capture Source</quote>, <quote>Capture Switch</quote> + and <quote>Capture Volume</quote> are used for the global + capture (input) source, switch and volume. Similarly, + <quote>Playback Switch</quote> and <quote>Playback + Volume</quote> are used for the global output gain switch and + volume. + </para> + </section> + + <section id="control-interface-control-names-tone"> + <title>Tone-controls</title> + <para> + tone-control switch and volumes are specified like + <quote>Tone Control - XXX</quote>, e.g. <quote>Tone Control - + Switch</quote>, <quote>Tone Control - Bass</quote>, + <quote>Tone Control - Center</quote>. + </para> + </section> + + <section id="control-interface-control-names-3d"> + <title>3D controls</title> + <para> + 3D-control switches and volumes are specified like <quote>3D + Control - XXX</quote>, e.g. <quote>3D Control - + Switch</quote>, <quote>3D Control - Center</quote>, <quote>3D + Control - Space</quote>. + </para> + </section> + + <section id="control-interface-control-names-mic"> + <title>Mic boost</title> + <para> + Mic-boost switch is set as <quote>Mic Boost</quote> or + <quote>Mic Boost (6dB)</quote>. + </para> + + <para> + More precise information can be found in + <filename>Documentation/sound/alsa/ControlNames.txt</filename>. + </para> + </section> + </section> + + <section id="control-interface-access-flags"> + <title>Access Flags</title> + + <para> + The access flag is the bitmask which specifies the access type + of the given control. The default access type is + <constant>SNDRV_CTL_ELEM_ACCESS_READWRITE</constant>, + which means both read and write are allowed to this control. + When the access flag is omitted (i.e. = 0), it is + considered as <constant>READWRITE</constant> access as default. + </para> + + <para> + When the control is read-only, pass + <constant>SNDRV_CTL_ELEM_ACCESS_READ</constant> instead. + In this case, you don't have to define + the <structfield>put</structfield> callback. + Similarly, when the control is write-only (although it's a rare + case), you can use the <constant>WRITE</constant> flag instead, and + you don't need the <structfield>get</structfield> callback. + </para> + + <para> + If the control value changes frequently (e.g. the VU meter), + <constant>VOLATILE</constant> flag should be given. This means + that the control may be changed without + <link linkend="control-interface-change-notification"><citetitle> + notification</citetitle></link>. Applications should poll such + a control constantly. + </para> + + <para> + When the control is inactive, set + the <constant>INACTIVE</constant> flag, too. + There are <constant>LOCK</constant> and + <constant>OWNER</constant> flags to change the write + permissions. + </para> + + </section> + + <section id="control-interface-callbacks"> + <title>Callbacks</title> + + <section id="control-interface-callbacks-info"> + <title>info callback</title> + <para> + The <structfield>info</structfield> callback is used to get + detailed information on this control. This must store the + values of the given struct <structname>snd_ctl_elem_info</structname> + object. For example, for a boolean control with a single + element: + + <example> + <title>Example of info callback</title> + <programlisting> +<![CDATA[ + static int snd_myctl_mono_info(struct snd_kcontrol *kcontrol, + struct snd_ctl_elem_info *uinfo) + { + uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN; + uinfo->count = 1; + uinfo->value.integer.min = 0; + uinfo->value.integer.max = 1; + return 0; + } +]]> + </programlisting> + </example> + </para> + + <para> + The <structfield>type</structfield> field specifies the type + of the control. There are <constant>BOOLEAN</constant>, + <constant>INTEGER</constant>, <constant>ENUMERATED</constant>, + <constant>BYTES</constant>, <constant>IEC958</constant> and + <constant>INTEGER64</constant>. The + <structfield>count</structfield> field specifies the + number of elements in this control. For example, a stereo + volume would have count = 2. The + <structfield>value</structfield> field is a union, and + the values stored are depending on the type. The boolean and + integer types are identical. + </para> + + <para> + The enumerated type is a bit different from others. You'll + need to set the string for the currently given item index. + + <informalexample> + <programlisting> +<![CDATA[ + static int snd_myctl_enum_info(struct snd_kcontrol *kcontrol, + struct snd_ctl_elem_info *uinfo) + { + static char *texts[4] = { + "First", "Second", "Third", "Fourth" + }; + uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED; + uinfo->count = 1; + uinfo->value.enumerated.items = 4; + if (uinfo->value.enumerated.item > 3) + uinfo->value.enumerated.item = 3; + strcpy(uinfo->value.enumerated.name, + texts[uinfo->value.enumerated.item]); + return 0; + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + Some common info callbacks are available for your convenience: + <function>snd_ctl_boolean_mono_info()</function> and + <function>snd_ctl_boolean_stereo_info()</function>. + Obviously, the former is an info callback for a mono channel + boolean item, just like <function>snd_myctl_mono_info</function> + above, and the latter is for a stereo channel boolean item. + </para> + + </section> + + <section id="control-interface-callbacks-get"> + <title>get callback</title> + + <para> + This callback is used to read the current value of the + control and to return to user-space. + </para> + + <para> + For example, + + <example> + <title>Example of get callback</title> + <programlisting> +<![CDATA[ + static int snd_myctl_get(struct snd_kcontrol *kcontrol, + struct snd_ctl_elem_value *ucontrol) + { + struct mychip *chip = snd_kcontrol_chip(kcontrol); + ucontrol->value.integer.value[0] = get_some_value(chip); + return 0; + } +]]> + </programlisting> + </example> + </para> + + <para> + The <structfield>value</structfield> field depends on + the type of control as well as on the info callback. For example, + the sb driver uses this field to store the register offset, + the bit-shift and the bit-mask. The + <structfield>private_value</structfield> field is set as follows: + <informalexample> + <programlisting> +<![CDATA[ + .private_value = reg | (shift << 16) | (mask << 24) +]]> + </programlisting> + </informalexample> + and is retrieved in callbacks like + <informalexample> + <programlisting> +<![CDATA[ + static int snd_sbmixer_get_single(struct snd_kcontrol *kcontrol, + struct snd_ctl_elem_value *ucontrol) + { + int reg = kcontrol->private_value & 0xff; + int shift = (kcontrol->private_value >> 16) & 0xff; + int mask = (kcontrol->private_value >> 24) & 0xff; + .... + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + In the <structfield>get</structfield> callback, + you have to fill all the elements if the + control has more than one elements, + i.e. <structfield>count</structfield> > 1. + In the example above, we filled only one element + (<structfield>value.integer.value[0]</structfield>) since it's + assumed as <structfield>count</structfield> = 1. + </para> + </section> + + <section id="control-interface-callbacks-put"> + <title>put callback</title> + + <para> + This callback is used to write a value from user-space. + </para> + + <para> + For example, + + <example> + <title>Example of put callback</title> + <programlisting> +<![CDATA[ + static int snd_myctl_put(struct snd_kcontrol *kcontrol, + struct snd_ctl_elem_value *ucontrol) + { + struct mychip *chip = snd_kcontrol_chip(kcontrol); + int changed = 0; + if (chip->current_value != + ucontrol->value.integer.value[0]) { + change_current_value(chip, + ucontrol->value.integer.value[0]); + changed = 1; + } + return changed; + } +]]> + </programlisting> + </example> + + As seen above, you have to return 1 if the value is + changed. If the value is not changed, return 0 instead. + If any fatal error happens, return a negative error code as + usual. + </para> + + <para> + As in the <structfield>get</structfield> callback, + when the control has more than one elements, + all elements must be evaluated in this callback, too. + </para> + </section> + + <section id="control-interface-callbacks-all"> + <title>Callbacks are not atomic</title> + <para> + All these three callbacks are basically not atomic. + </para> + </section> + </section> + + <section id="control-interface-constructor"> + <title>Constructor</title> + <para> + When everything is ready, finally we can create a new + control. To create a control, there are two functions to be + called, <function>snd_ctl_new1()</function> and + <function>snd_ctl_add()</function>. + </para> + + <para> + In the simplest way, you can do like this: + + <informalexample> + <programlisting> +<![CDATA[ + err = snd_ctl_add(card, snd_ctl_new1(&my_control, chip)); + if (err < 0) + return err; +]]> + </programlisting> + </informalexample> + + where <parameter>my_control</parameter> is the + struct <structname>snd_kcontrol_new</structname> object defined above, and chip + is the object pointer to be passed to + kcontrol->private_data + which can be referred to in callbacks. + </para> + + <para> + <function>snd_ctl_new1()</function> allocates a new + <structname>snd_kcontrol</structname> instance (that's why the definition + of <parameter>my_control</parameter> can be with + the <parameter>__devinitdata</parameter> + prefix), and <function>snd_ctl_add</function> assigns the given + control component to the card. + </para> + </section> + + <section id="control-interface-change-notification"> + <title>Change Notification</title> + <para> + If you need to change and update a control in the interrupt + routine, you can call <function>snd_ctl_notify()</function>. For + example, + + <informalexample> + <programlisting> +<![CDATA[ + snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, id_pointer); +]]> + </programlisting> + </informalexample> + + This function takes the card pointer, the event-mask, and the + control id pointer for the notification. The event-mask + specifies the types of notification, for example, in the above + example, the change of control values is notified. + The id pointer is the pointer of struct <structname>snd_ctl_elem_id</structname> + to be notified. + You can find some examples in <filename>es1938.c</filename> or + <filename>es1968.c</filename> for hardware volume interrupts. + </para> + </section> + + <section id="control-interface-tlv"> + <title>Metadata</title> + <para> + To provide information about the dB values of a mixer control, use + on of the <constant>DECLARE_TLV_xxx</constant> macros from + <filename><sound/tlv.h></filename> to define a variable + containing this information, set the<structfield>tlv.p + </structfield> field to point to this variable, and include the + <constant>SNDRV_CTL_ELEM_ACCESS_TLV_READ</constant> flag in the + <structfield>access</structfield> field; like this: + <informalexample> + <programlisting> +<![CDATA[ + static DECLARE_TLV_DB_SCALE(db_scale_my_control, -4050, 150, 0); + + static struct snd_kcontrol_new my_control __devinitdata = { + ... + .access = SNDRV_CTL_ELEM_ACCESS_READWRITE | + SNDRV_CTL_ELEM_ACCESS_TLV_READ, + ... + .tlv.p = db_scale_my_control, + }; +]]> + </programlisting> + </informalexample> + </para> + + <para> + The <function>DECLARE_TLV_DB_SCALE</function> macro defines + information about a mixer control where each step in the control's + value changes the dB value by a constant dB amount. + The first parameter is the name of the variable to be defined. + The second parameter is the minimum value, in units of 0.01 dB. + The third parameter is the step size, in units of 0.01 dB. + Set the fourth parameter to 1 if the minimum value actually mutes + the control. + </para> + + <para> + The <function>DECLARE_TLV_DB_LINEAR</function> macro defines + information about a mixer control where the control's value affects + the output linearly. + The first parameter is the name of the variable to be defined. + The second parameter is the minimum value, in units of 0.01 dB. + The third parameter is the maximum value, in units of 0.01 dB. + If the minimum value mutes the control, set the second parameter to + <constant>TLV_DB_GAIN_MUTE</constant>. + </para> + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- API for AC97 Codec --> +<!-- ****************************************************** --> + <chapter id="api-ac97"> + <title>API for AC97 Codec</title> + + <section> + <title>General</title> + <para> + The ALSA AC97 codec layer is a well-defined one, and you don't + have to write much code to control it. Only low-level control + routines are necessary. The AC97 codec API is defined in + <filename><sound/ac97_codec.h></filename>. + </para> + </section> + + <section id="api-ac97-example"> + <title>Full Code Example</title> + <para> + <example> + <title>Example of AC97 Interface</title> + <programlisting> +<![CDATA[ + struct mychip { + .... + struct snd_ac97 *ac97; + .... + }; + + static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, + unsigned short reg) + { + struct mychip *chip = ac97->private_data; + .... + /* read a register value here from the codec */ + return the_register_value; + } + + static void snd_mychip_ac97_write(struct snd_ac97 *ac97, + unsigned short reg, unsigned short val) + { + struct mychip *chip = ac97->private_data; + .... + /* write the given register value to the codec */ + } + + static int snd_mychip_ac97(struct mychip *chip) + { + struct snd_ac97_bus *bus; + struct snd_ac97_template ac97; + int err; + static struct snd_ac97_bus_ops ops = { + .write = snd_mychip_ac97_write, + .read = snd_mychip_ac97_read, + }; + + err = snd_ac97_bus(chip->card, 0, &ops, NULL, &bus); + if (err < 0) + return err; + memset(&ac97, 0, sizeof(ac97)); + ac97.private_data = chip; + return snd_ac97_mixer(bus, &ac97, &chip->ac97); + } + +]]> + </programlisting> + </example> + </para> + </section> + + <section id="api-ac97-constructor"> + <title>Constructor</title> + <para> + To create an ac97 instance, first call <function>snd_ac97_bus</function> + with an <type>ac97_bus_ops_t</type> record with callback functions. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_ac97_bus *bus; + static struct snd_ac97_bus_ops ops = { + .write = snd_mychip_ac97_write, + .read = snd_mychip_ac97_read, + }; + + snd_ac97_bus(card, 0, &ops, NULL, &pbus); +]]> + </programlisting> + </informalexample> + + The bus record is shared among all belonging ac97 instances. + </para> + + <para> + And then call <function>snd_ac97_mixer()</function> with an + struct <structname>snd_ac97_template</structname> + record together with the bus pointer created above. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_ac97_template ac97; + int err; + + memset(&ac97, 0, sizeof(ac97)); + ac97.private_data = chip; + snd_ac97_mixer(bus, &ac97, &chip->ac97); +]]> + </programlisting> + </informalexample> + + where chip->ac97 is a pointer to a newly created + <type>ac97_t</type> instance. + In this case, the chip pointer is set as the private data, so that + the read/write callback functions can refer to this chip instance. + This instance is not necessarily stored in the chip + record. If you need to change the register values from the + driver, or need the suspend/resume of ac97 codecs, keep this + pointer to pass to the corresponding functions. + </para> + </section> + + <section id="api-ac97-callbacks"> + <title>Callbacks</title> + <para> + The standard callbacks are <structfield>read</structfield> and + <structfield>write</structfield>. Obviously they + correspond to the functions for read and write accesses to the + hardware low-level codes. + </para> + + <para> + The <structfield>read</structfield> callback returns the + register value specified in the argument. + + <informalexample> + <programlisting> +<![CDATA[ + static unsigned short snd_mychip_ac97_read(struct snd_ac97 *ac97, + unsigned short reg) + { + struct mychip *chip = ac97->private_data; + .... + return the_register_value; + } +]]> + </programlisting> + </informalexample> + + Here, the chip can be cast from ac97->private_data. + </para> + + <para> + Meanwhile, the <structfield>write</structfield> callback is + used to set the register value. + + <informalexample> + <programlisting> +<![CDATA[ + static void snd_mychip_ac97_write(struct snd_ac97 *ac97, + unsigned short reg, unsigned short val) +]]> + </programlisting> + </informalexample> + </para> + + <para> + These callbacks are non-atomic like the control API callbacks. + </para> + + <para> + There are also other callbacks: + <structfield>reset</structfield>, + <structfield>wait</structfield> and + <structfield>init</structfield>. + </para> + + <para> + The <structfield>reset</structfield> callback is used to reset + the codec. If the chip requires a special kind of reset, you can + define this callback. + </para> + + <para> + The <structfield>wait</structfield> callback is used to + add some waiting time in the standard initialization of the codec. If the + chip requires the extra waiting time, define this callback. + </para> + + <para> + The <structfield>init</structfield> callback is used for + additional initialization of the codec. + </para> + </section> + + <section id="api-ac97-updating-registers"> + <title>Updating Registers in The Driver</title> + <para> + If you need to access to the codec from the driver, you can + call the following functions: + <function>snd_ac97_write()</function>, + <function>snd_ac97_read()</function>, + <function>snd_ac97_update()</function> and + <function>snd_ac97_update_bits()</function>. + </para> + + <para> + Both <function>snd_ac97_write()</function> and + <function>snd_ac97_update()</function> functions are used to + set a value to the given register + (<constant>AC97_XXX</constant>). The difference between them is + that <function>snd_ac97_update()</function> doesn't write a + value if the given value has been already set, while + <function>snd_ac97_write()</function> always rewrites the + value. + + <informalexample> + <programlisting> +<![CDATA[ + snd_ac97_write(ac97, AC97_MASTER, 0x8080); + snd_ac97_update(ac97, AC97_MASTER, 0x8080); +]]> + </programlisting> + </informalexample> + </para> + + <para> + <function>snd_ac97_read()</function> is used to read the value + of the given register. For example, + + <informalexample> + <programlisting> +<![CDATA[ + value = snd_ac97_read(ac97, AC97_MASTER); +]]> + </programlisting> + </informalexample> + </para> + + <para> + <function>snd_ac97_update_bits()</function> is used to update + some bits in the given register. + + <informalexample> + <programlisting> +<![CDATA[ + snd_ac97_update_bits(ac97, reg, mask, value); +]]> + </programlisting> + </informalexample> + </para> + + <para> + Also, there is a function to change the sample rate (of a + given register such as + <constant>AC97_PCM_FRONT_DAC_RATE</constant>) when VRA or + DRA is supported by the codec: + <function>snd_ac97_set_rate()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + snd_ac97_set_rate(ac97, AC97_PCM_FRONT_DAC_RATE, 44100); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The following registers are available to set the rate: + <constant>AC97_PCM_MIC_ADC_RATE</constant>, + <constant>AC97_PCM_FRONT_DAC_RATE</constant>, + <constant>AC97_PCM_LR_ADC_RATE</constant>, + <constant>AC97_SPDIF</constant>. When + <constant>AC97_SPDIF</constant> is specified, the register is + not really changed but the corresponding IEC958 status bits will + be updated. + </para> + </section> + + <section id="api-ac97-clock-adjustment"> + <title>Clock Adjustment</title> + <para> + In some chips, the clock of the codec isn't 48000 but using a + PCI clock (to save a quartz!). In this case, change the field + bus->clock to the corresponding + value. For example, intel8x0 + and es1968 drivers have their own function to read from the clock. + </para> + </section> + + <section id="api-ac97-proc-files"> + <title>Proc Files</title> + <para> + The ALSA AC97 interface will create a proc file such as + <filename>/proc/asound/card0/codec97#0/ac97#0-0</filename> and + <filename>ac97#0-0+regs</filename>. You can refer to these files to + see the current status and registers of the codec. + </para> + </section> + + <section id="api-ac97-multiple-codecs"> + <title>Multiple Codecs</title> + <para> + When there are several codecs on the same card, you need to + call <function>snd_ac97_mixer()</function> multiple times with + ac97.num=1 or greater. The <structfield>num</structfield> field + specifies the codec number. + </para> + + <para> + If you set up multiple codecs, you either need to write + different callbacks for each codec or check + ac97->num in the callback routines. + </para> + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- MIDI (MPU401-UART) Interface --> +<!-- ****************************************************** --> + <chapter id="midi-interface"> + <title>MIDI (MPU401-UART) Interface</title> + + <section id="midi-interface-general"> + <title>General</title> + <para> + Many soundcards have built-in MIDI (MPU401-UART) + interfaces. When the soundcard supports the standard MPU401-UART + interface, most likely you can use the ALSA MPU401-UART API. The + MPU401-UART API is defined in + <filename><sound/mpu401.h></filename>. + </para> + + <para> + Some soundchips have a similar but slightly different + implementation of mpu401 stuff. For example, emu10k1 has its own + mpu401 routines. + </para> + </section> + + <section id="midi-interface-constructor"> + <title>Constructor</title> + <para> + To create a rawmidi object, call + <function>snd_mpu401_uart_new()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_rawmidi *rmidi; + snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags, + irq, irq_flags, &rmidi); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The first argument is the card pointer, and the second is the + index of this component. You can create up to 8 rawmidi + devices. + </para> + + <para> + The third argument is the type of the hardware, + <constant>MPU401_HW_XXX</constant>. If it's not a special one, + you can use <constant>MPU401_HW_MPU401</constant>. + </para> + + <para> + The 4th argument is the I/O port address. Many + backward-compatible MPU401 have an I/O port such as 0x330. Or, it + might be a part of its own PCI I/O region. It depends on the + chip design. + </para> + + <para> + The 5th argument is a bitflag for additional information. + When the I/O port address above is part of the PCI I/O + region, the MPU401 I/O port might have been already allocated + (reserved) by the driver itself. In such a case, pass a bit flag + <constant>MPU401_INFO_INTEGRATED</constant>, + and the mpu401-uart layer will allocate the I/O ports by itself. + </para> + + <para> + When the controller supports only the input or output MIDI stream, + pass the <constant>MPU401_INFO_INPUT</constant> or + <constant>MPU401_INFO_OUTPUT</constant> bitflag, respectively. + Then the rawmidi instance is created as a single stream. + </para> + + <para> + <constant>MPU401_INFO_MMIO</constant> bitflag is used to change + the access method to MMIO (via readb and writeb) instead of + iob and outb. In this case, you have to pass the iomapped address + to <function>snd_mpu401_uart_new()</function>. + </para> + + <para> + When <constant>MPU401_INFO_TX_IRQ</constant> is set, the output + stream isn't checked in the default interrupt handler. The driver + needs to call <function>snd_mpu401_uart_interrupt_tx()</function> + by itself to start processing the output stream in the irq handler. + </para> + + <para> + Usually, the port address corresponds to the command port and + port + 1 corresponds to the data port. If not, you may change + the <structfield>cport</structfield> field of + struct <structname>snd_mpu401</structname> manually + afterward. However, <structname>snd_mpu401</structname> pointer is not + returned explicitly by + <function>snd_mpu401_uart_new()</function>. You need to cast + rmidi->private_data to + <structname>snd_mpu401</structname> explicitly, + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_mpu401 *mpu; + mpu = rmidi->private_data; +]]> + </programlisting> + </informalexample> + + and reset the cport as you like: + + <informalexample> + <programlisting> +<![CDATA[ + mpu->cport = my_own_control_port; +]]> + </programlisting> + </informalexample> + </para> + + <para> + The 6th argument specifies the irq number for UART. If the irq + is already allocated, pass 0 to the 7th argument + (<parameter>irq_flags</parameter>). Otherwise, pass the flags + for irq allocation + (<constant>SA_XXX</constant> bits) to it, and the irq will be + reserved by the mpu401-uart layer. If the card doesn't generate + UART interrupts, pass -1 as the irq number. Then a timer + interrupt will be invoked for polling. + </para> + </section> + + <section id="midi-interface-interrupt-handler"> + <title>Interrupt Handler</title> + <para> + When the interrupt is allocated in + <function>snd_mpu401_uart_new()</function>, the private + interrupt handler is used, hence you don't have anything else to do + than creating the mpu401 stuff. Otherwise, you have to call + <function>snd_mpu401_uart_interrupt()</function> explicitly when + a UART interrupt is invoked and checked in your own interrupt + handler. + </para> + + <para> + In this case, you need to pass the private_data of the + returned rawmidi object from + <function>snd_mpu401_uart_new()</function> as the second + argument of <function>snd_mpu401_uart_interrupt()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + snd_mpu401_uart_interrupt(irq, rmidi->private_data, regs); +]]> + </programlisting> + </informalexample> + </para> + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- RawMIDI Interface --> +<!-- ****************************************************** --> + <chapter id="rawmidi-interface"> + <title>RawMIDI Interface</title> + + <section id="rawmidi-interface-overview"> + <title>Overview</title> + + <para> + The raw MIDI interface is used for hardware MIDI ports that can + be accessed as a byte stream. It is not used for synthesizer + chips that do not directly understand MIDI. + </para> + + <para> + ALSA handles file and buffer management. All you have to do is + to write some code to move data between the buffer and the + hardware. + </para> + + <para> + The rawmidi API is defined in + <filename><sound/rawmidi.h></filename>. + </para> + </section> + + <section id="rawmidi-interface-constructor"> + <title>Constructor</title> + + <para> + To create a rawmidi device, call the + <function>snd_rawmidi_new</function> function: + <informalexample> + <programlisting> +<![CDATA[ + struct snd_rawmidi *rmidi; + err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi); + if (err < 0) + return err; + rmidi->private_data = chip; + strcpy(rmidi->name, "My MIDI"); + rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT | + SNDRV_RAWMIDI_INFO_INPUT | + SNDRV_RAWMIDI_INFO_DUPLEX; +]]> + </programlisting> + </informalexample> + </para> + + <para> + The first argument is the card pointer, the second argument is + the ID string. + </para> + + <para> + The third argument is the index of this component. You can + create up to 8 rawmidi devices. + </para> + + <para> + The fourth and fifth arguments are the number of output and + input substreams, respectively, of this device (a substream is + the equivalent of a MIDI port). + </para> + + <para> + Set the <structfield>info_flags</structfield> field to specify + the capabilities of the device. + Set <constant>SNDRV_RAWMIDI_INFO_OUTPUT</constant> if there is + at least one output port, + <constant>SNDRV_RAWMIDI_INFO_INPUT</constant> if there is at + least one input port, + and <constant>SNDRV_RAWMIDI_INFO_DUPLEX</constant> if the device + can handle output and input at the same time. + </para> + + <para> + After the rawmidi device is created, you need to set the + operators (callbacks) for each substream. There are helper + functions to set the operators for all the substreams of a device: + <informalexample> + <programlisting> +<![CDATA[ + snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops); + snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The operators are usually defined like this: + <informalexample> + <programlisting> +<![CDATA[ + static struct snd_rawmidi_ops snd_mymidi_output_ops = { + .open = snd_mymidi_output_open, + .close = snd_mymidi_output_close, + .trigger = snd_mymidi_output_trigger, + }; +]]> + </programlisting> + </informalexample> + These callbacks are explained in the <link + linkend="rawmidi-interface-callbacks"><citetitle>Callbacks</citetitle></link> + section. + </para> + + <para> + If there are more than one substream, you should give a + unique name to each of them: + <informalexample> + <programlisting> +<![CDATA[ + struct snd_rawmidi_substream *substream; + list_for_each_entry(substream, + &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams, + list { + sprintf(substream->name, "My MIDI Port %d", substream->number + 1); + } + /* same for SNDRV_RAWMIDI_STREAM_INPUT */ +]]> + </programlisting> + </informalexample> + </para> + </section> + + <section id="rawmidi-interface-callbacks"> + <title>Callbacks</title> + + <para> + In all the callbacks, the private data that you've set for the + rawmidi device can be accessed as + substream->rmidi->private_data. + <!-- <code> isn't available before DocBook 4.3 --> + </para> + + <para> + If there is more than one port, your callbacks can determine the + port index from the struct snd_rawmidi_substream data passed to each + callback: + <informalexample> + <programlisting> +<![CDATA[ + struct snd_rawmidi_substream *substream; + int index = substream->number; +]]> + </programlisting> + </informalexample> + </para> + + <section id="rawmidi-interface-op-open"> + <title><function>open</function> callback</title> + + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_open(struct snd_rawmidi_substream *substream); +]]> + </programlisting> + </informalexample> + + <para> + This is called when a substream is opened. + You can initialize the hardware here, but you shouldn't + start transmitting/receiving data yet. + </para> + </section> + + <section id="rawmidi-interface-op-close"> + <title><function>close</function> callback</title> + + <informalexample> + <programlisting> +<![CDATA[ + static int snd_xxx_close(struct snd_rawmidi_substream *substream); +]]> + </programlisting> + </informalexample> + + <para> + Guess what. + </para> + + <para> + The <function>open</function> and <function>close</function> + callbacks of a rawmidi device are serialized with a mutex, + and can sleep. + </para> + </section> + + <section id="rawmidi-interface-op-trigger-out"> + <title><function>trigger</function> callback for output + substreams</title> + + <informalexample> + <programlisting> +<![CDATA[ + static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up); +]]> + </programlisting> + </informalexample> + + <para> + This is called with a nonzero <parameter>up</parameter> + parameter when there is some data in the substream buffer that + must be transmitted. + </para> + + <para> + To read data from the buffer, call + <function>snd_rawmidi_transmit_peek</function>. It will + return the number of bytes that have been read; this will be + less than the number of bytes requested when there are no more + data in the buffer. + After the data have been transmitted successfully, call + <function>snd_rawmidi_transmit_ack</function> to remove the + data from the substream buffer: + <informalexample> + <programlisting> +<![CDATA[ + unsigned char data; + while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) { + if (snd_mychip_try_to_transmit(data)) + snd_rawmidi_transmit_ack(substream, 1); + else + break; /* hardware FIFO full */ + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + If you know beforehand that the hardware will accept data, you + can use the <function>snd_rawmidi_transmit</function> function + which reads some data and removes them from the buffer at once: + <informalexample> + <programlisting> +<![CDATA[ + while (snd_mychip_transmit_possible()) { + unsigned char data; + if (snd_rawmidi_transmit(substream, &data, 1) != 1) + break; /* no more data */ + snd_mychip_transmit(data); + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + If you know beforehand how many bytes you can accept, you can + use a buffer size greater than one with the + <function>snd_rawmidi_transmit*</function> functions. + </para> + + <para> + The <function>trigger</function> callback must not sleep. If + the hardware FIFO is full before the substream buffer has been + emptied, you have to continue transmitting data later, either + in an interrupt handler, or with a timer if the hardware + doesn't have a MIDI transmit interrupt. + </para> + + <para> + The <function>trigger</function> callback is called with a + zero <parameter>up</parameter> parameter when the transmission + of data should be aborted. + </para> + </section> + + <section id="rawmidi-interface-op-trigger-in"> + <title><function>trigger</function> callback for input + substreams</title> + + <informalexample> + <programlisting> +<![CDATA[ + static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up); +]]> + </programlisting> + </informalexample> + + <para> + This is called with a nonzero <parameter>up</parameter> + parameter to enable receiving data, or with a zero + <parameter>up</parameter> parameter do disable receiving data. + </para> + + <para> + The <function>trigger</function> callback must not sleep; the + actual reading of data from the device is usually done in an + interrupt handler. + </para> + + <para> + When data reception is enabled, your interrupt handler should + call <function>snd_rawmidi_receive</function> for all received + data: + <informalexample> + <programlisting> +<![CDATA[ + void snd_mychip_midi_interrupt(...) + { + while (mychip_midi_available()) { + unsigned char data; + data = mychip_midi_read(); + snd_rawmidi_receive(substream, &data, 1); + } + } +]]> + </programlisting> + </informalexample> + </para> + </section> + + <section id="rawmidi-interface-op-drain"> + <title><function>drain</function> callback</title> + + <informalexample> + <programlisting> +<![CDATA[ + static void snd_xxx_drain(struct snd_rawmidi_substream *substream); +]]> + </programlisting> + </informalexample> + + <para> + This is only used with output substreams. This function should wait + until all data read from the substream buffer have been transmitted. + This ensures that the device can be closed and the driver unloaded + without losing data. + </para> + + <para> + This callback is optional. If you do not set + <structfield>drain</structfield> in the struct snd_rawmidi_ops + structure, ALSA will simply wait for 50 milliseconds + instead. + </para> + </section> + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- Miscellaneous Devices --> +<!-- ****************************************************** --> + <chapter id="misc-devices"> + <title>Miscellaneous Devices</title> + + <section id="misc-devices-opl3"> + <title>FM OPL3</title> + <para> + The FM OPL3 is still used in many chips (mainly for backward + compatibility). ALSA has a nice OPL3 FM control layer, too. The + OPL3 API is defined in + <filename><sound/opl3.h></filename>. + </para> + + <para> + FM registers can be directly accessed through the direct-FM API, + defined in <filename><sound/asound_fm.h></filename>. In + ALSA native mode, FM registers are accessed through + the Hardware-Dependant Device direct-FM extension API, whereas in + OSS compatible mode, FM registers can be accessed with the OSS + direct-FM compatible API in <filename>/dev/dmfmX</filename> device. + </para> + + <para> + To create the OPL3 component, you have two functions to + call. The first one is a constructor for the <type>opl3_t</type> + instance. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_opl3 *opl3; + snd_opl3_create(card, lport, rport, OPL3_HW_OPL3_XXX, + integrated, &opl3); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The first argument is the card pointer, the second one is the + left port address, and the third is the right port address. In + most cases, the right port is placed at the left port + 2. + </para> + + <para> + The fourth argument is the hardware type. + </para> + + <para> + When the left and right ports have been already allocated by + the card driver, pass non-zero to the fifth argument + (<parameter>integrated</parameter>). Otherwise, the opl3 module will + allocate the specified ports by itself. + </para> + + <para> + When the accessing the hardware requires special method + instead of the standard I/O access, you can create opl3 instance + separately with <function>snd_opl3_new()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_opl3 *opl3; + snd_opl3_new(card, OPL3_HW_OPL3_XXX, &opl3); +]]> + </programlisting> + </informalexample> + </para> + + <para> + Then set <structfield>command</structfield>, + <structfield>private_data</structfield> and + <structfield>private_free</structfield> for the private + access function, the private data and the destructor. + The l_port and r_port are not necessarily set. Only the + command must be set properly. You can retrieve the data + from the opl3->private_data field. + </para> + + <para> + After creating the opl3 instance via <function>snd_opl3_new()</function>, + call <function>snd_opl3_init()</function> to initialize the chip to the + proper state. Note that <function>snd_opl3_create()</function> always + calls it internally. + </para> + + <para> + If the opl3 instance is created successfully, then create a + hwdep device for this opl3. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_hwdep *opl3hwdep; + snd_opl3_hwdep_new(opl3, 0, 1, &opl3hwdep); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The first argument is the <type>opl3_t</type> instance you + created, and the second is the index number, usually 0. + </para> + + <para> + The third argument is the index-offset for the sequencer + client assigned to the OPL3 port. When there is an MPU401-UART, + give 1 for here (UART always takes 0). + </para> + </section> + + <section id="misc-devices-hardware-dependent"> + <title>Hardware-Dependent Devices</title> + <para> + Some chips need user-space access for special + controls or for loading the micro code. In such a case, you can + create a hwdep (hardware-dependent) device. The hwdep API is + defined in <filename><sound/hwdep.h></filename>. You can + find examples in opl3 driver or + <filename>isa/sb/sb16_csp.c</filename>. + </para> + + <para> + The creation of the <type>hwdep</type> instance is done via + <function>snd_hwdep_new()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_hwdep *hw; + snd_hwdep_new(card, "My HWDEP", 0, &hw); +]]> + </programlisting> + </informalexample> + + where the third argument is the index number. + </para> + + <para> + You can then pass any pointer value to the + <parameter>private_data</parameter>. + If you assign a private data, you should define the + destructor, too. The destructor function is set in + the <structfield>private_free</structfield> field. + + <informalexample> + <programlisting> +<![CDATA[ + struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL); + hw->private_data = p; + hw->private_free = mydata_free; +]]> + </programlisting> + </informalexample> + + and the implementation of the destructor would be: + + <informalexample> + <programlisting> +<![CDATA[ + static void mydata_free(struct snd_hwdep *hw) + { + struct mydata *p = hw->private_data; + kfree(p); + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + The arbitrary file operations can be defined for this + instance. The file operators are defined in + the <parameter>ops</parameter> table. For example, assume that + this chip needs an ioctl. + + <informalexample> + <programlisting> +<![CDATA[ + hw->ops.open = mydata_open; + hw->ops.ioctl = mydata_ioctl; + hw->ops.release = mydata_release; +]]> + </programlisting> + </informalexample> + + And implement the callback functions as you like. + </para> + </section> + + <section id="misc-devices-IEC958"> + <title>IEC958 (S/PDIF)</title> + <para> + Usually the controls for IEC958 devices are implemented via + the control interface. There is a macro to compose a name string for + IEC958 controls, <function>SNDRV_CTL_NAME_IEC958()</function> + defined in <filename><include/asound.h></filename>. + </para> + + <para> + There are some standard controls for IEC958 status bits. These + controls use the type <type>SNDRV_CTL_ELEM_TYPE_IEC958</type>, + and the size of element is fixed as 4 bytes array + (value.iec958.status[x]). For the <structfield>info</structfield> + callback, you don't specify + the value field for this type (the count field must be set, + though). + </para> + + <para> + <quote>IEC958 Playback Con Mask</quote> is used to return the + bit-mask for the IEC958 status bits of consumer mode. Similarly, + <quote>IEC958 Playback Pro Mask</quote> returns the bitmask for + professional mode. They are read-only controls, and are defined + as MIXER controls (iface = + <constant>SNDRV_CTL_ELEM_IFACE_MIXER</constant>). + </para> + + <para> + Meanwhile, <quote>IEC958 Playback Default</quote> control is + defined for getting and setting the current default IEC958 + bits. Note that this one is usually defined as a PCM control + (iface = <constant>SNDRV_CTL_ELEM_IFACE_PCM</constant>), + although in some places it's defined as a MIXER control. + </para> + + <para> + In addition, you can define the control switches to + enable/disable or to set the raw bit mode. The implementation + will depend on the chip, but the control should be named as + <quote>IEC958 xxx</quote>, preferably using + the <function>SNDRV_CTL_NAME_IEC958()</function> macro. + </para> + + <para> + You can find several cases, for example, + <filename>pci/emu10k1</filename>, + <filename>pci/ice1712</filename>, or + <filename>pci/cmipci.c</filename>. + </para> + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- Buffer and Memory Management --> +<!-- ****************************************************** --> + <chapter id="buffer-and-memory"> + <title>Buffer and Memory Management</title> + + <section id="buffer-and-memory-buffer-types"> + <title>Buffer Types</title> + <para> + ALSA provides several different buffer allocation functions + depending on the bus and the architecture. All these have a + consistent API. The allocation of physically-contiguous pages is + done via + <function>snd_malloc_xxx_pages()</function> function, where xxx + is the bus type. + </para> + + <para> + The allocation of pages with fallback is + <function>snd_malloc_xxx_pages_fallback()</function>. This + function tries to allocate the specified pages but if the pages + are not available, it tries to reduce the page sizes until + enough space is found. + </para> + + <para> + The release the pages, call + <function>snd_free_xxx_pages()</function> function. + </para> + + <para> + Usually, ALSA drivers try to allocate and reserve + a large contiguous physical space + at the time the module is loaded for the later use. + This is called <quote>pre-allocation</quote>. + As already written, you can call the following function at + pcm instance construction time (in the case of PCI bus). + + <informalexample> + <programlisting> +<![CDATA[ + snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV, + snd_dma_pci_data(pci), size, max); +]]> + </programlisting> + </informalexample> + + where <parameter>size</parameter> is the byte size to be + pre-allocated and the <parameter>max</parameter> is the maximum + size to be changed via the <filename>prealloc</filename> proc file. + The allocator will try to get an area as large as possible + within the given size. + </para> + + <para> + The second argument (type) and the third argument (device pointer) + are dependent on the bus. + In the case of the ISA bus, pass <function>snd_dma_isa_data()</function> + as the third argument with <constant>SNDRV_DMA_TYPE_DEV</constant> type. + For the continuous buffer unrelated to the bus can be pre-allocated + with <constant>SNDRV_DMA_TYPE_CONTINUOUS</constant> type and the + <function>snd_dma_continuous_data(GFP_KERNEL)</function> device pointer, + where <constant>GFP_KERNEL</constant> is the kernel allocation flag to + use. + For the PCI scatter-gather buffers, use + <constant>SNDRV_DMA_TYPE_DEV_SG</constant> with + <function>snd_dma_pci_data(pci)</function> + (see the + <link linkend="buffer-and-memory-non-contiguous"><citetitle>Non-Contiguous Buffers + </citetitle></link> section). + </para> + + <para> + Once the buffer is pre-allocated, you can use the + allocator in the <structfield>hw_params</structfield> callback: + + <informalexample> + <programlisting> +<![CDATA[ + snd_pcm_lib_malloc_pages(substream, size); +]]> + </programlisting> + </informalexample> + + Note that you have to pre-allocate to use this function. + </para> + </section> + + <section id="buffer-and-memory-external-hardware"> + <title>External Hardware Buffers</title> + <para> + Some chips have their own hardware buffers and the DMA + transfer from the host memory is not available. In such a case, + you need to either 1) copy/set the audio data directly to the + external hardware buffer, or 2) make an intermediate buffer and + copy/set the data from it to the external hardware buffer in + interrupts (or in tasklets, preferably). + </para> + + <para> + The first case works fine if the external hardware buffer is large + enough. This method doesn't need any extra buffers and thus is + more effective. You need to define the + <structfield>copy</structfield> and + <structfield>silence</structfield> callbacks for + the data transfer. However, there is a drawback: it cannot + be mmapped. The examples are GUS's GF1 PCM or emu8000's + wavetable PCM. + </para> + + <para> + The second case allows for mmap on the buffer, although you have + to handle an interrupt or a tasklet to transfer the data + from the intermediate buffer to the hardware buffer. You can find an + example in the vxpocket driver. + </para> + + <para> + Another case is when the chip uses a PCI memory-map + region for the buffer instead of the host memory. In this case, + mmap is available only on certain architectures like the Intel one. + In non-mmap mode, the data cannot be transferred as in the normal + way. Thus you need to define the <structfield>copy</structfield> and + <structfield>silence</structfield> callbacks as well, + as in the cases above. The examples are found in + <filename>rme32.c</filename> and <filename>rme96.c</filename>. + </para> + + <para> + The implementation of the <structfield>copy</structfield> and + <structfield>silence</structfield> callbacks depends upon + whether the hardware supports interleaved or non-interleaved + samples. The <structfield>copy</structfield> callback is + defined like below, a bit + differently depending whether the direction is playback or + capture: + + <informalexample> + <programlisting> +<![CDATA[ + static int playback_copy(struct snd_pcm_substream *substream, int channel, + snd_pcm_uframes_t pos, void *src, snd_pcm_uframes_t count); + static int capture_copy(struct snd_pcm_substream *substream, int channel, + snd_pcm_uframes_t pos, void *dst, snd_pcm_uframes_t count); +]]> + </programlisting> + </informalexample> + </para> + + <para> + In the case of interleaved samples, the second argument + (<parameter>channel</parameter>) is not used. The third argument + (<parameter>pos</parameter>) points the + current position offset in frames. + </para> + + <para> + The meaning of the fourth argument is different between + playback and capture. For playback, it holds the source data + pointer, and for capture, it's the destination data pointer. + </para> + + <para> + The last argument is the number of frames to be copied. + </para> + + <para> + What you have to do in this callback is again different + between playback and capture directions. In the + playback case, you copy the given amount of data + (<parameter>count</parameter>) at the specified pointer + (<parameter>src</parameter>) to the specified offset + (<parameter>pos</parameter>) on the hardware buffer. When + coded like memcpy-like way, the copy would be like: + + <informalexample> + <programlisting> +<![CDATA[ + my_memcpy(my_buffer + frames_to_bytes(runtime, pos), src, + frames_to_bytes(runtime, count)); +]]> + </programlisting> + </informalexample> + </para> + + <para> + For the capture direction, you copy the given amount of + data (<parameter>count</parameter>) at the specified offset + (<parameter>pos</parameter>) on the hardware buffer to the + specified pointer (<parameter>dst</parameter>). + + <informalexample> + <programlisting> +<![CDATA[ + my_memcpy(dst, my_buffer + frames_to_bytes(runtime, pos), + frames_to_bytes(runtime, count)); +]]> + </programlisting> + </informalexample> + + Note that both the position and the amount of data are given + in frames. + </para> + + <para> + In the case of non-interleaved samples, the implementation + will be a bit more complicated. + </para> + + <para> + You need to check the channel argument, and if it's -1, copy + the whole channels. Otherwise, you have to copy only the + specified channel. Please check + <filename>isa/gus/gus_pcm.c</filename> as an example. + </para> + + <para> + The <structfield>silence</structfield> callback is also + implemented in a similar way. + + <informalexample> + <programlisting> +<![CDATA[ + static int silence(struct snd_pcm_substream *substream, int channel, + snd_pcm_uframes_t pos, snd_pcm_uframes_t count); +]]> + </programlisting> + </informalexample> + </para> + + <para> + The meanings of arguments are the same as in the + <structfield>copy</structfield> + callback, although there is no <parameter>src/dst</parameter> + argument. In the case of interleaved samples, the channel + argument has no meaning, as well as on + <structfield>copy</structfield> callback. + </para> + + <para> + The role of <structfield>silence</structfield> callback is to + set the given amount + (<parameter>count</parameter>) of silence data at the + specified offset (<parameter>pos</parameter>) on the hardware + buffer. Suppose that the data format is signed (that is, the + silent-data is 0), and the implementation using a memset-like + function would be like: + + <informalexample> + <programlisting> +<![CDATA[ + my_memcpy(my_buffer + frames_to_bytes(runtime, pos), 0, + frames_to_bytes(runtime, count)); +]]> + </programlisting> + </informalexample> + </para> + + <para> + In the case of non-interleaved samples, again, the + implementation becomes a bit more complicated. See, for example, + <filename>isa/gus/gus_pcm.c</filename>. + </para> + </section> + + <section id="buffer-and-memory-non-contiguous"> + <title>Non-Contiguous Buffers</title> + <para> + If your hardware supports the page table as in emu10k1 or the + buffer descriptors as in via82xx, you can use the scatter-gather + (SG) DMA. ALSA provides an interface for handling SG-buffers. + The API is provided in <filename><sound/pcm.h></filename>. + </para> + + <para> + For creating the SG-buffer handler, call + <function>snd_pcm_lib_preallocate_pages()</function> or + <function>snd_pcm_lib_preallocate_pages_for_all()</function> + with <constant>SNDRV_DMA_TYPE_DEV_SG</constant> + in the PCM constructor like other PCI pre-allocator. + You need to pass <function>snd_dma_pci_data(pci)</function>, + where pci is the struct <structname>pci_dev</structname> pointer + of the chip as well. + The <type>struct snd_sg_buf</type> instance is created as + substream->dma_private. You can cast + the pointer like: + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_sg_buf *sgbuf = (struct snd_sg_buf *)substream->dma_private; +]]> + </programlisting> + </informalexample> + </para> + + <para> + Then call <function>snd_pcm_lib_malloc_pages()</function> + in the <structfield>hw_params</structfield> callback + as well as in the case of normal PCI buffer. + The SG-buffer handler will allocate the non-contiguous kernel + pages of the given size and map them onto the virtually contiguous + memory. The virtual pointer is addressed in runtime->dma_area. + The physical address (runtime->dma_addr) is set to zero, + because the buffer is physically non-contigous. + The physical address table is set up in sgbuf->table. + You can get the physical address at a certain offset via + <function>snd_pcm_sgbuf_get_addr()</function>. + </para> + + <para> + When a SG-handler is used, you need to set + <function>snd_pcm_sgbuf_ops_page</function> as + the <structfield>page</structfield> callback. + (See <link linkend="pcm-interface-operators-page-callback"> + <citetitle>page callback section</citetitle></link>.) + </para> + + <para> + To release the data, call + <function>snd_pcm_lib_free_pages()</function> in the + <structfield>hw_free</structfield> callback as usual. + </para> + </section> + + <section id="buffer-and-memory-vmalloced"> + <title>Vmalloc'ed Buffers</title> + <para> + It's possible to use a buffer allocated via + <function>vmalloc</function>, for example, for an intermediate + buffer. Since the allocated pages are not contiguous, you need + to set the <structfield>page</structfield> callback to obtain + the physical address at every offset. + </para> + + <para> + The implementation of <structfield>page</structfield> callback + would be like this: + + <informalexample> + <programlisting> +<![CDATA[ + #include <linux/vmalloc.h> + + /* get the physical page pointer on the given offset */ + static struct page *mychip_page(struct snd_pcm_substream *substream, + unsigned long offset) + { + void *pageptr = substream->runtime->dma_area + offset; + return vmalloc_to_page(pageptr); + } +]]> + </programlisting> + </informalexample> + </para> + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- Proc Interface --> +<!-- ****************************************************** --> + <chapter id="proc-interface"> + <title>Proc Interface</title> + <para> + ALSA provides an easy interface for procfs. The proc files are + very useful for debugging. I recommend you set up proc files if + you write a driver and want to get a running status or register + dumps. The API is found in + <filename><sound/info.h></filename>. + </para> + + <para> + To create a proc file, call + <function>snd_card_proc_new()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + struct snd_info_entry *entry; + int err = snd_card_proc_new(card, "my-file", &entry); +]]> + </programlisting> + </informalexample> + + where the second argument specifies the name of the proc file to be + created. The above example will create a file + <filename>my-file</filename> under the card directory, + e.g. <filename>/proc/asound/card0/my-file</filename>. + </para> + + <para> + Like other components, the proc entry created via + <function>snd_card_proc_new()</function> will be registered and + released automatically in the card registration and release + functions. + </para> + + <para> + When the creation is successful, the function stores a new + instance in the pointer given in the third argument. + It is initialized as a text proc file for read only. To use + this proc file as a read-only text file as it is, set the read + callback with a private data via + <function>snd_info_set_text_ops()</function>. + + <informalexample> + <programlisting> +<![CDATA[ + snd_info_set_text_ops(entry, chip, my_proc_read); +]]> + </programlisting> + </informalexample> + + where the second argument (<parameter>chip</parameter>) is the + private data to be used in the callbacks. The third parameter + specifies the read buffer size and the fourth + (<parameter>my_proc_read</parameter>) is the callback function, which + is defined like + + <informalexample> + <programlisting> +<![CDATA[ + static void my_proc_read(struct snd_info_entry *entry, + struct snd_info_buffer *buffer); +]]> + </programlisting> + </informalexample> + + </para> + + <para> + In the read callback, use <function>snd_iprintf()</function> for + output strings, which works just like normal + <function>printf()</function>. For example, + + <informalexample> + <programlisting> +<![CDATA[ + static void my_proc_read(struct snd_info_entry *entry, + struct snd_info_buffer *buffer) + { + struct my_chip *chip = entry->private_data; + + snd_iprintf(buffer, "This is my chip!\n"); + snd_iprintf(buffer, "Port = %ld\n", chip->port); + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + The file permissions can be changed afterwards. As default, it's + set as read only for all users. If you want to add write + permission for the user (root as default), do as follows: + + <informalexample> + <programlisting> +<![CDATA[ + entry->mode = S_IFREG | S_IRUGO | S_IWUSR; +]]> + </programlisting> + </informalexample> + + and set the write buffer size and the callback + + <informalexample> + <programlisting> +<![CDATA[ + entry->c.text.write = my_proc_write; +]]> + </programlisting> + </informalexample> + </para> + + <para> + For the write callback, you can use + <function>snd_info_get_line()</function> to get a text line, and + <function>snd_info_get_str()</function> to retrieve a string from + the line. Some examples are found in + <filename>core/oss/mixer_oss.c</filename>, core/oss/and + <filename>pcm_oss.c</filename>. + </para> + + <para> + For a raw-data proc-file, set the attributes as follows: + + <informalexample> + <programlisting> +<![CDATA[ + static struct snd_info_entry_ops my_file_io_ops = { + .read = my_file_io_read, + }; + + entry->content = SNDRV_INFO_CONTENT_DATA; + entry->private_data = chip; + entry->c.ops = &my_file_io_ops; + entry->size = 4096; + entry->mode = S_IFREG | S_IRUGO; +]]> + </programlisting> + </informalexample> + </para> + + <para> + The callback is much more complicated than the text-file + version. You need to use a low-level I/O functions such as + <function>copy_from/to_user()</function> to transfer the + data. + + <informalexample> + <programlisting> +<![CDATA[ + static long my_file_io_read(struct snd_info_entry *entry, + void *file_private_data, + struct file *file, + char *buf, + unsigned long count, + unsigned long pos) + { + long size = count; + if (pos + size > local_max_size) + size = local_max_size - pos; + if (copy_to_user(buf, local_data + pos, size)) + return -EFAULT; + return size; + } +]]> + </programlisting> + </informalexample> + </para> + + </chapter> + + +<!-- ****************************************************** --> +<!-- Power Management --> +<!-- ****************************************************** --> + <chapter id="power-management"> + <title>Power Management</title> + <para> + If the chip is supposed to work with suspend/resume + functions, you need to add power-management code to the + driver. The additional code for power-management should be + <function>ifdef</function>'ed with + <constant>CONFIG_PM</constant>. + </para> + + <para> + If the driver <emphasis>fully</emphasis> supports suspend/resume + that is, the device can be + properly resumed to its state when suspend was called, + you can set the <constant>SNDRV_PCM_INFO_RESUME</constant> flag + in the pcm info field. Usually, this is possible when the + registers of the chip can be safely saved and restored to + RAM. If this is set, the trigger callback is called with + <constant>SNDRV_PCM_TRIGGER_RESUME</constant> after the resume + callback completes. + </para> + + <para> + Even if the driver doesn't support PM fully but + partial suspend/resume is still possible, it's still worthy to + implement suspend/resume callbacks. In such a case, applications + would reset the status by calling + <function>snd_pcm_prepare()</function> and restart the stream + appropriately. Hence, you can define suspend/resume callbacks + below but don't set <constant>SNDRV_PCM_INFO_RESUME</constant> + info flag to the PCM. + </para> + + <para> + Note that the trigger with SUSPEND can always be called when + <function>snd_pcm_suspend_all</function> is called, + regardless of the <constant>SNDRV_PCM_INFO_RESUME</constant> flag. + The <constant>RESUME</constant> flag affects only the behavior + of <function>snd_pcm_resume()</function>. + (Thus, in theory, + <constant>SNDRV_PCM_TRIGGER_RESUME</constant> isn't needed + to be handled in the trigger callback when no + <constant>SNDRV_PCM_INFO_RESUME</constant> flag is set. But, + it's better to keep it for compatibility reasons.) + </para> + <para> + In the earlier version of ALSA drivers, a common + power-management layer was provided, but it has been removed. + The driver needs to define the suspend/resume hooks according to + the bus the device is connected to. In the case of PCI drivers, the + callbacks look like below: + + <informalexample> + <programlisting> +<![CDATA[ + #ifdef CONFIG_PM + static int snd_my_suspend(struct pci_dev *pci, pm_message_t state) + { + .... /* do things for suspend */ + return 0; + } + static int snd_my_resume(struct pci_dev *pci) + { + .... /* do things for suspend */ + return 0; + } + #endif +]]> + </programlisting> + </informalexample> + </para> + + <para> + The scheme of the real suspend job is as follows. + + <orderedlist> + <listitem><para>Retrieve the card and the chip data.</para></listitem> + <listitem><para>Call <function>snd_power_change_state()</function> with + <constant>SNDRV_CTL_POWER_D3hot</constant> to change the + power status.</para></listitem> + <listitem><para>Call <function>snd_pcm_suspend_all()</function> to suspend the running PCM streams.</para></listitem> + <listitem><para>If AC97 codecs are used, call + <function>snd_ac97_suspend()</function> for each codec.</para></listitem> + <listitem><para>Save the register values if necessary.</para></listitem> + <listitem><para>Stop the hardware if necessary.</para></listitem> + <listitem><para>Disable the PCI device by calling + <function>pci_disable_device()</function>. Then, call + <function>pci_save_state()</function> at last.</para></listitem> + </orderedlist> + </para> + + <para> + A typical code would be like: + + <informalexample> + <programlisting> +<![CDATA[ + static int mychip_suspend(struct pci_dev *pci, pm_message_t state) + { + /* (1) */ + struct snd_card *card = pci_get_drvdata(pci); + struct mychip *chip = card->private_data; + /* (2) */ + snd_power_change_state(card, SNDRV_CTL_POWER_D3hot); + /* (3) */ + snd_pcm_suspend_all(chip->pcm); + /* (4) */ + snd_ac97_suspend(chip->ac97); + /* (5) */ + snd_mychip_save_registers(chip); + /* (6) */ + snd_mychip_stop_hardware(chip); + /* (7) */ + pci_disable_device(pci); + pci_save_state(pci); + return 0; + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + The scheme of the real resume job is as follows. + + <orderedlist> + <listitem><para>Retrieve the card and the chip data.</para></listitem> + <listitem><para>Set up PCI. First, call <function>pci_restore_state()</function>. + Then enable the pci device again by calling <function>pci_enable_device()</function>. + Call <function>pci_set_master()</function> if necessary, too.</para></listitem> + <listitem><para>Re-initialize the chip.</para></listitem> + <listitem><para>Restore the saved registers if necessary.</para></listitem> + <listitem><para>Resume the mixer, e.g. calling + <function>snd_ac97_resume()</function>.</para></listitem> + <listitem><para>Restart the hardware (if any).</para></listitem> + <listitem><para>Call <function>snd_power_change_state()</function> with + <constant>SNDRV_CTL_POWER_D0</constant> to notify the processes.</para></listitem> + </orderedlist> + </para> + + <para> + A typical code would be like: + + <informalexample> + <programlisting> +<![CDATA[ + static int mychip_resume(struct pci_dev *pci) + { + /* (1) */ + struct snd_card *card = pci_get_drvdata(pci); + struct mychip *chip = card->private_data; + /* (2) */ + pci_restore_state(pci); + pci_enable_device(pci); + pci_set_master(pci); + /* (3) */ + snd_mychip_reinit_chip(chip); + /* (4) */ + snd_mychip_restore_registers(chip); + /* (5) */ + snd_ac97_resume(chip->ac97); + /* (6) */ + snd_mychip_restart_chip(chip); + /* (7) */ + snd_power_change_state(card, SNDRV_CTL_POWER_D0); + return 0; + } +]]> + </programlisting> + </informalexample> + </para> + + <para> + As shown in the above, it's better to save registers after + suspending the PCM operations via + <function>snd_pcm_suspend_all()</function> or + <function>snd_pcm_suspend()</function>. It means that the PCM + streams are already stoppped when the register snapshot is + taken. But, remember that you don't have to restart the PCM + stream in the resume callback. It'll be restarted via + trigger call with <constant>SNDRV_PCM_TRIGGER_RESUME</constant> + when necessary. + </para> + + <para> + OK, we have all callbacks now. Let's set them up. In the + initialization of the card, make sure that you can get the chip + data from the card instance, typically via + <structfield>private_data</structfield> field, in case you + created the chip data individually. + + <informalexample> + <programlisting> +<![CDATA[ + static int __devinit snd_mychip_probe(struct pci_dev *pci, + const struct pci_device_id *pci_id) + { + .... + struct snd_card *card; + struct mychip *chip; + int err; + .... + err = snd_card_create(index[dev], id[dev], THIS_MODULE, 0, &card); + .... + chip = kzalloc(sizeof(*chip), GFP_KERNEL); + .... + card->private_data = chip; + .... + } +]]> + </programlisting> + </informalexample> + + When you created the chip data with + <function>snd_card_create()</function>, it's anyway accessible + via <structfield>private_data</structfield> field. + + <informalexample> + <programlisting> +<![CDATA[ + static int __devinit snd_mychip_probe(struct pci_dev *pci, + const struct pci_device_id *pci_id) + { + .... + struct snd_card *card; + struct mychip *chip; + int err; + .... + err = snd_card_create(index[dev], id[dev], THIS_MODULE, + sizeof(struct mychip), &card); + .... + chip = card->private_data; + .... + } +]]> + </programlisting> + </informalexample> + + </para> + + <para> + If you need a space to save the registers, allocate the + buffer for it here, too, since it would be fatal + if you cannot allocate a memory in the suspend phase. + The allocated buffer should be released in the corresponding + destructor. + </para> + + <para> + And next, set suspend/resume callbacks to the pci_driver. + + <informalexample> + <programlisting> +<![CDATA[ + static struct pci_driver driver = { + .name = "My Chip", + .id_table = snd_my_ids, + .probe = snd_my_probe, + .remove = __devexit_p(snd_my_remove), + #ifdef CONFIG_PM + .suspend = snd_my_suspend, + .resume = snd_my_resume, + #endif + }; +]]> + </programlisting> + </informalexample> + </para> + + </chapter> + + +<!-- ****************************************************** --> +<!-- Module Parameters --> +<!-- ****************************************************** --> + <chapter id="module-parameters"> + <title>Module Parameters</title> + <para> + There are standard module options for ALSA. At least, each + module should have the <parameter>index</parameter>, + <parameter>id</parameter> and <parameter>enable</parameter> + options. + </para> + + <para> + If the module supports multiple cards (usually up to + 8 = <constant>SNDRV_CARDS</constant> cards), they should be + arrays. The default initial values are defined already as + constants for easier programming: + + <informalexample> + <programlisting> +<![CDATA[ + static int index[SNDRV_CARDS] = SNDRV_DEFAULT_IDX; + static char *id[SNDRV_CARDS] = SNDRV_DEFAULT_STR; + static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP; +]]> + </programlisting> + </informalexample> + </para> + + <para> + If the module supports only a single card, they could be single + variables, instead. <parameter>enable</parameter> option is not + always necessary in this case, but it would be better to have a + dummy option for compatibility. + </para> + + <para> + The module parameters must be declared with the standard + <function>module_param()()</function>, + <function>module_param_array()()</function> and + <function>MODULE_PARM_DESC()</function> macros. + </para> + + <para> + The typical coding would be like below: + + <informalexample> + <programlisting> +<![CDATA[ + #define CARD_NAME "My Chip" + + module_param_array(index, int, NULL, 0444); + MODULE_PARM_DESC(index, "Index value for " CARD_NAME " soundcard."); + module_param_array(id, charp, NULL, 0444); + MODULE_PARM_DESC(id, "ID string for " CARD_NAME " soundcard."); + module_param_array(enable, bool, NULL, 0444); + MODULE_PARM_DESC(enable, "Enable " CARD_NAME " soundcard."); +]]> + </programlisting> + </informalexample> + </para> + + <para> + Also, don't forget to define the module description, classes, + license and devices. Especially, the recent modprobe requires to + define the module license as GPL, etc., otherwise the system is + shown as <quote>tainted</quote>. + + <informalexample> + <programlisting> +<![CDATA[ + MODULE_DESCRIPTION("My Chip"); + MODULE_LICENSE("GPL"); + MODULE_SUPPORTED_DEVICE("{{Vendor,My Chip Name}}"); +]]> + </programlisting> + </informalexample> + </para> + + </chapter> + + +<!-- ****************************************************** --> +<!-- How To Put Your Driver --> +<!-- ****************************************************** --> + <chapter id="how-to-put-your-driver"> + <title>How To Put Your Driver Into ALSA Tree</title> + <section> + <title>General</title> + <para> + So far, you've learned how to write the driver codes. + And you might have a question now: how to put my own + driver into the ALSA driver tree? + Here (finally :) the standard procedure is described briefly. + </para> + + <para> + Suppose that you create a new PCI driver for the card + <quote>xyz</quote>. The card module name would be + snd-xyz. The new driver is usually put into the alsa-driver + tree, <filename>alsa-driver/pci</filename> directory in + the case of PCI cards. + Then the driver is evaluated, audited and tested + by developers and users. After a certain time, the driver + will go to the alsa-kernel tree (to the corresponding directory, + such as <filename>alsa-kernel/pci</filename>) and eventually + will be integrated into the Linux 2.6 tree (the directory would be + <filename>linux/sound/pci</filename>). + </para> + + <para> + In the following sections, the driver code is supposed + to be put into alsa-driver tree. The two cases are covered: + a driver consisting of a single source file and one consisting + of several source files. + </para> + </section> + + <section> + <title>Driver with A Single Source File</title> + <para> + <orderedlist> + <listitem> + <para> + Modify alsa-driver/pci/Makefile + </para> + + <para> + Suppose you have a file xyz.c. Add the following + two lines + <informalexample> + <programlisting> +<![CDATA[ + snd-xyz-objs := xyz.o + obj-$(CONFIG_SND_XYZ) += snd-xyz.o +]]> + </programlisting> + </informalexample> + </para> + </listitem> + + <listitem> + <para> + Create the Kconfig entry + </para> + + <para> + Add the new entry of Kconfig for your xyz driver. + <informalexample> + <programlisting> +<![CDATA[ + config SND_XYZ + tristate "Foobar XYZ" + depends on SND + select SND_PCM + help + Say Y here to include support for Foobar XYZ soundcard. + + To compile this driver as a module, choose M here: the module + will be called snd-xyz. +]]> + </programlisting> + </informalexample> + + the line, select SND_PCM, specifies that the driver xyz supports + PCM. In addition to SND_PCM, the following components are + supported for select command: + SND_RAWMIDI, SND_TIMER, SND_HWDEP, SND_MPU401_UART, + SND_OPL3_LIB, SND_OPL4_LIB, SND_VX_LIB, SND_AC97_CODEC. + Add the select command for each supported component. + </para> + + <para> + Note that some selections imply the lowlevel selections. + For example, PCM includes TIMER, MPU401_UART includes RAWMIDI, + AC97_CODEC includes PCM, and OPL3_LIB includes HWDEP. + You don't need to give the lowlevel selections again. + </para> + + <para> + For the details of Kconfig script, refer to the kbuild + documentation. + </para> + + </listitem> + + <listitem> + <para> + Run cvscompile script to re-generate the configure script and + build the whole stuff again. + </para> + </listitem> + </orderedlist> + </para> + </section> + + <section> + <title>Drivers with Several Source Files</title> + <para> + Suppose that the driver snd-xyz have several source files. + They are located in the new subdirectory, + pci/xyz. + + <orderedlist> + <listitem> + <para> + Add a new directory (<filename>xyz</filename>) in + <filename>alsa-driver/pci/Makefile</filename> as below + + <informalexample> + <programlisting> +<![CDATA[ + obj-$(CONFIG_SND) += xyz/ +]]> + </programlisting> + </informalexample> + </para> + </listitem> + + <listitem> + <para> + Under the directory <filename>xyz</filename>, create a Makefile + + <example> + <title>Sample Makefile for a driver xyz</title> + <programlisting> +<![CDATA[ + ifndef SND_TOPDIR + SND_TOPDIR=../.. + endif + + include $(SND_TOPDIR)/toplevel.config + include $(SND_TOPDIR)/Makefile.conf + + snd-xyz-objs := xyz.o abc.o def.o + + obj-$(CONFIG_SND_XYZ) += snd-xyz.o + + include $(SND_TOPDIR)/Rules.make +]]> + </programlisting> + </example> + </para> + </listitem> + + <listitem> + <para> + Create the Kconfig entry + </para> + + <para> + This procedure is as same as in the last section. + </para> + </listitem> + + <listitem> + <para> + Run cvscompile script to re-generate the configure script and + build the whole stuff again. + </para> + </listitem> + </orderedlist> + </para> + </section> + + </chapter> + +<!-- ****************************************************** --> +<!-- Useful Functions --> +<!-- ****************************************************** --> + <chapter id="useful-functions"> + <title>Useful Functions</title> + + <section id="useful-functions-snd-printk"> + <title><function>snd_printk()</function> and friends</title> + <para> + ALSA provides a verbose version of the + <function>printk()</function> function. If a kernel config + <constant>CONFIG_SND_VERBOSE_PRINTK</constant> is set, this + function prints the given message together with the file name + and the line of the caller. The <constant>KERN_XXX</constant> + prefix is processed as + well as the original <function>printk()</function> does, so it's + recommended to add this prefix, e.g. + + <informalexample> + <programlisting> +<![CDATA[ + snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\n"); +]]> + </programlisting> + </informalexample> + </para> + + <para> + There are also <function>printk()</function>'s for + debugging. <function>snd_printd()</function> can be used for + general debugging purposes. If + <constant>CONFIG_SND_DEBUG</constant> is set, this function is + compiled, and works just like + <function>snd_printk()</function>. If the ALSA is compiled + without the debugging flag, it's ignored. + </para> + + <para> + <function>snd_printdd()</function> is compiled in only when + <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is set. Please note + that <constant>CONFIG_SND_DEBUG_VERBOSE</constant> is not set as default + even if you configure the alsa-driver with + <option>--with-debug=full</option> option. You need to give + explicitly <option>--with-debug=detect</option> option instead. + </para> + </section> + + <section id="useful-functions-snd-bug"> + <title><function>snd_BUG()</function></title> + <para> + It shows the <computeroutput>BUG?</computeroutput> message and + stack trace as well as <function>snd_BUG_ON</function> at the point. + It's useful to show that a fatal error happens there. + </para> + <para> + When no debug flag is set, this macro is ignored. + </para> + </section> + + <section id="useful-functions-snd-bug-on"> + <title><function>snd_BUG_ON()</function></title> + <para> + <function>snd_BUG_ON()</function> macro is similar with + <function>WARN_ON()</function> macro. For example, + + <informalexample> + <programlisting> +<![CDATA[ + snd_BUG_ON(!pointer); +]]> + </programlisting> + </informalexample> + + or it can be used as the condition, + <informalexample> + <programlisting> +<![CDATA[ + if (snd_BUG_ON(non_zero_is_bug)) + return -EINVAL; +]]> + </programlisting> + </informalexample> + + </para> + + <para> + The macro takes an conditional expression to evaluate. + When <constant>CONFIG_SND_DEBUG</constant>, is set, the + expression is actually evaluated. If it's non-zero, it shows + the warning message such as + <computeroutput>BUG? (xxx)</computeroutput> + normally followed by stack trace. It returns the evaluated + value. + When no <constant>CONFIG_SND_DEBUG</constant> is set, this + macro always returns zero. + </para> + + </section> + + </chapter> + + +<!-- ****************************************************** --> +<!-- Acknowledgments --> +<!-- ****************************************************** --> + <chapter id="acknowledgments"> + <title>Acknowledgments</title> + <para> + I would like to thank Phil Kerr for his help for improvement and + corrections of this document. + </para> + <para> + Kevin Conder reformatted the original plain-text to the + DocBook format. + </para> + <para> + Giuliano Pochini corrected typos and contributed the example codes + in the hardware constraints section. + </para> + </chapter> +</book> |