diff options
author | Kumar Gala <galak@kernel.crashing.org> | 2007-02-12 23:57:21 -0600 |
---|---|---|
committer | Kumar Gala <galak@kernel.crashing.org> | 2007-02-12 23:57:21 -0600 |
commit | 54c66f6d781e03dc0b23956234963c4911e6d1c0 (patch) | |
tree | 40619a66ae6d8703a57bf681d087ffeabbffd346 /Documentation/sound/alsa/soc/overview.txt | |
parent | 8ce0a7df6e6117d8814e976d4b7ce6a6b2c9cf93 (diff) | |
parent | 17e0e27020d028a790d97699aff85a43af5be472 (diff) |
Merge branch 'master' into 85xx
Diffstat (limited to 'Documentation/sound/alsa/soc/overview.txt')
-rw-r--r-- | Documentation/sound/alsa/soc/overview.txt | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/Documentation/sound/alsa/soc/overview.txt b/Documentation/sound/alsa/soc/overview.txt new file mode 100644 index 00000000000..753c5cc5984 --- /dev/null +++ b/Documentation/sound/alsa/soc/overview.txt @@ -0,0 +1,83 @@ +ALSA SoC Layer +============== + +The overall project goal of the ALSA System on Chip (ASoC) layer is to provide +better ALSA support for embedded system on chip procesors (e.g. pxa2xx, au1x00, +iMX, etc) and portable audio codecs. Currently there is some support in the +kernel for SoC audio, however it has some limitations:- + + * Currently, codec drivers are often tightly coupled to the underlying SoC + cpu. This is not ideal and leads to code duplication i.e. Linux now has 4 + different wm8731 drivers for 4 different SoC platforms. + + * There is no standard method to signal user initiated audio events. + e.g. Headphone/Mic insertion, Headphone/Mic detection after an insertion + event. These are quite common events on portable devices and ofter require + machine specific code to re route audio, enable amps etc after such an event. + + * Current drivers tend to power up the entire codec when playing + (or recording) audio. This is fine for a PC, but tends to waste a lot of + power on portable devices. There is also no support for saving power via + changing codec oversampling rates, bias currents, etc. + + +ASoC Design +=========== + +The ASoC layer is designed to address these issues and provide the following +features :- + + * Codec independence. Allows reuse of codec drivers on other platforms + and machines. + + * Easy I2S/PCM audio interface setup between codec and SoC. Each SoC interface + and codec registers it's audio interface capabilities with the core and are + subsequently matched and configured when the application hw params are known. + + * Dynamic Audio Power Management (DAPM). DAPM automatically sets the codec to + it's minimum power state at all times. This includes powering up/down + internal power blocks depending on the internal codec audio routing and any + active streams. + + * Pop and click reduction. Pops and clicks can be reduced by powering the + codec up/down in the correct sequence (including using digital mute). ASoC + signals the codec when to change power states. + + * Machine specific controls: Allow machines to add controls to the sound card + e.g. volume control for speaker amp. + +To achieve all this, ASoC basically splits an embedded audio system into 3 +components :- + + * Codec driver: The codec driver is platform independent and contains audio + controls, audio interface capabilities, codec dapm definition and codec IO + functions. + + * Platform driver: The platform driver contains the audio dma engine and audio + interface drivers (e.g. I2S, AC97, PCM) for that platform. + + * Machine driver: The machine driver handles any machine specific controls and + audio events. i.e. turing on an amp at start of playback. + + +Documentation +============= + +The documentation is spilt into the following sections:- + +overview.txt: This file. + +codec.txt: Codec driver internals. + +DAI.txt: Description of Digital Audio Interface standards and how to configure +a DAI within your codec and CPU DAI drivers. + +dapm.txt: Dynamic Audio Power Management + +platform.txt: Platform audio DMA and DAI. + +machine.txt: Machine driver internals. + +pop_clicks.txt: How to minimise audio artifacts. + +clocking.txt: ASoC clocking for best power performance.
\ No newline at end of file |