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Enhanced mmap_begin and mmap_commit descriptions

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Jaroslav Kysela 2001-11-01 07:46:59 +00:00
parent 7c7352a009
commit daffd8f1bf
1 changed files with 33 additions and 7 deletions
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38
src/pcm/pcm.c
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@ -4301,13 +4301,20 @@ void snd_pcm_info_set_stream(snd_pcm_info_t *obj, snd_pcm_stream_t val)
} }
/** /**
* \brief Application request to access a portion of mmap area * \brief Application request to access a portion of direct (mmap) area
* \param pcm PCM handle * \param pcm PCM handle
* \param areas Returned mmap channel areas * \param areas Returned mmap channel areas
* \param offset Returned mmap area offset * \param offset Returned mmap area offset
* \param size mmap area portion size (wanted on entry, contiguous * \param size mmap area portion size (wanted on entry, contiguous available on exit)
available on exit)
* \return 0 on success otherwise a negative error code * \return 0 on success otherwise a negative error code
*
* The function should be called before a sample-direct area can be accessed.
* The resulting size parameter is always less or equal to the input count of frames
* and can be zero, if no frames can be processed (the ring buffer is full).
*
* See the snd_pcm_mmap_commit() function to finish the frame processing in
* the direct areas.
*
*/ */
int snd_pcm_mmap_begin(snd_pcm_t *pcm, int snd_pcm_mmap_begin(snd_pcm_t *pcm,
const snd_pcm_channel_area_t **areas, const snd_pcm_channel_area_t **areas,
@ -4336,13 +4343,32 @@ int snd_pcm_mmap_begin(snd_pcm_t *pcm,
} }
/** /**
* \brief Application has completed the access to area requested with * \brief Application has completed the access to area requested with #snd_pcm_mmap_begin
#snd_pcm_mmap_begin
* \param pcm PCM handle * \param pcm PCM handle
* \return 0 on success otherwise a negative error code * \return 0 on success otherwise a negative error code
* *
* To call this with offset/frames values different from that returned * To call this with offset/frames values different from that returned
* by snd_pcm_mmap_begin has undefined effects and it has to be avoided. * by snd_pcm_mmap_begin() has undefined effects and it has to be avoided.
*
* Example:
\code
double phase = 0;
const snd_pcm_area_t *areas;
snd_pcm_uframes_t offset, frames;
frames = frame_buffer_size;
err = snd_pcm_mmap_begin(pcm_handle, &areas, &offset, &frames);
if (err < 0)
error(err);
// this function fills the areas from offset with count of frames
generate_sine(areas, offset, frames, &phase);
err = snd_pcm_mmap_commit(pcm_handle, offset, frames);
if (err < 0)
error(err);
\endcode
*
* Look to the \ref example_test_pcm "Sine-wave generator" example
* for more details about the generate_sine function.
*/ */
int snd_pcm_mmap_commit(snd_pcm_t *pcm, snd_pcm_uframes_t offset, int snd_pcm_mmap_commit(snd_pcm_t *pcm, snd_pcm_uframes_t offset,
snd_pcm_uframes_t frames) snd_pcm_uframes_t frames)