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Diffstat (limited to 'Documentation/sound/alsa/soc/overview.txt')
| -rw-r--r-- | Documentation/sound/alsa/soc/overview.txt | 42 |
1 files changed, 22 insertions, 20 deletions
diff --git a/Documentation/sound/alsa/soc/overview.txt b/Documentation/sound/alsa/soc/overview.txt index c47ce953067..1e4c6d3655f 100644 --- a/Documentation/sound/alsa/soc/overview.txt +++ b/Documentation/sound/alsa/soc/overview.txt @@ -1,25 +1,26 @@ 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 processors (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:- +The overall project goal of the ALSA System on Chip (ASoC) layer is to +provide better ALSA support for embedded system-on-chip processors (e.g. +pxa2xx, au1x00, iMX, etc) and portable audio codecs. Prior to the ASoC +subsystem there was some support in the kernel for SoC audio, however it +had 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. + * Codec drivers were often tightly coupled to the underlying SoC + CPU. This is not ideal and leads to code duplication - for example, + Linux had different wm8731 drivers for 4 different SoC platforms. - * There is no standard method to signal user initiated audio events (e.g. + * There was 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 often 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. + * Drivers tended 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 was also no support for saving + power via changing codec oversampling rates, bias currents, etc. ASoC Design @@ -31,12 +32,13 @@ 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. + * 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 + hardware parameters 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 + its 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. @@ -45,16 +47,16 @@ features :- 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). + (e.g. volume control for speaker amplifier). 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 + controls, audio interface capabilities, codec DAPM definition and codec IO functions. - * Platform driver: The platform driver contains the audio dma engine and audio + * 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 @@ -81,4 +83,4 @@ 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 +clocking.txt: ASoC clocking for best power performance. |