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Added more explanation for i/o access

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Jaroslav Kysela 2002-03-27 18:39:42 +00:00
parent 708847237b
commit e131f156b5
1 changed files with 12 additions and 4 deletions
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16
src/pcm/pcm.c
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@ -224,18 +224,26 @@ embedded poll waiting implementation.
\subsection alsa_pcm_rw Read / Write transfer
There are two versions of read / write routines. The first expects the
interleaved samples at input, and the second one expects non-interleaved
(samples in separated buffers) at input. There are these functions for
interleaved transfers: \link ::snd_pcm_writei \endlink,
interleaved samples at input (#SND_PCM_ACCESS_RW_INTERLEAVED access method),
and the second one expects non-interleaved (samples in separated buffers -
#SND_PCM_ACCESS_RW_NONINTERLEAVED access method) at input. There are these
functions for interleaved transfers: \link ::snd_pcm_writei \endlink,
\link ::snd_pcm_readi \endlink. For non-interleaved transfers, there are
these functions: \link ::snd_pcm_writen \endlink and \link ::snd_pcm_readn
\endlink.
\subsection alsa_mmap_rw Direct Read / Write transfer (via mmap'ed areas)
Three kinds of organization of ring buffer memory areas exist in ALSA API.
Access #SND_PCM_ACCESS_MMAP_INTERLEAVED has interleaved samples. Access
#SND_PCM_ACCESS_MMAP_NONINTERLEAVED expects continous sample areas for
one channel. Access #SND_PCM_ACCESS_MMAP_COMPLEX does not fit to interleaved
and non-interleaved ring buffer organization.
\par
There are two functions for this kind of transfer. Application can get an
access to memory areas via \link ::snd_pcm_mmap_begin \endlink function.
This functions returns the areas (single area is equal to a channel)
This function returns the areas (single area is equal to a channel)
containing the direct pointers to memory and sample position description
in \link ::snd_pcm_channel_area_t \endlink structure. After application
transfers the data in the memory areas, then it must be acknowledged