mirrors/alsa-lib
1
0
Fork 0
mirror of https://github.com/alsa-project/alsa-lib.git synced 2025-12-15 08:56:36 -05:00
Code Issues Projects Releases Packages Wiki Activity Actions 1

Added general overview and PCM formats

Browse source
This commit is contained in:
Jaroslav Kysela 2001-10-15 15:31:58 +00:00
parent e441ec8013
commit 2f906af9b3
1 changed files with 21 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

21
doc/pcm.doxygen
View file

@ -50,6 +50,16 @@ to store just 5.46 seconds of sound in a megabyte of memory when using
to reduce memory and communication costs by compressing the recorded to reduce memory and communication costs by compressing the recorded
signal but this is beyond the scope of this document. </P> signal but this is beyond the scope of this document. </P>
\section pcm_general_overview General overview
ALSA uses the ring buffer to store outgoing (playback) and incoming (capture,
record) samples. There are two pointers being mantained to allow
a precise communication between application and device pointing to current
processed sample by hardware and last processed sample by application.
The modern audio chips allows to program the transfer time periods.
It means that the stream of samples is divided to small chunks. Device
acknowledges to application when the transfer of a chunk is complete.
\section pcm_open_behaviour Blocked and non-blocked open \section pcm_open_behaviour Blocked and non-blocked open
The ALSA PCM API uses a different behaviour when the device is opened The ALSA PCM API uses a different behaviour when the device is opened
@ -133,4 +143,15 @@ In other case, the calls \link ::snd_pcm_prepare() \endlink,
\link ::snd_pcm_drop() \endlink, \link ::snd_pcm_drain() \endlink can be used \link ::snd_pcm_drop() \endlink, \link ::snd_pcm_drain() \endlink can be used
to leave this state. to leave this state.
\section pcm_formats PCM formats
The full list of formats present the \link ::snd_pcm_format_t \endlink type.
The 24-bit linear samples uses 32-bit physical space, but the sample is
stored in low three bits. Some hardware does not support processing of full
range, thus you may get the significative bits for linear samples via
\link ::snd_pcm_hw_params_get_sbits \endlink function. The example: ICE1712
chips support 32-bit sample processing, but low byte is ignored (playback)
or zero (capture). The function \link ::snd_pcm_hw_params_get_sbits() \endlink
returns 24 in the case.
*/ */