[alsa-devel] Warning/error from ALSA’s pcm_min.c example. Possible problem?

[Raymond Yau]

2010/1/31 Louise Hoffman <louise.hoffman at gmail.com>

> Dear ALSA developers,
>
> When I compile ALSA's pcm_min.c[0] example with
>
> gcc -Wall -lasound pcm_min.c -o pcm_min
>
> Everything is fine, but running it, I get the white noise as expected,
> but I also get this warning/error:
>
> Short write (expected 16384, wrote 7616)
>
> Which comes from the last if-statement.
>
> One bug is in this line
>
>                frames = snd_pcm_writei(handle, buffer, sizeof(buffer));
>
> where "sizeof(buffer)" should be "number of frames in the buffer".
>
> But there are still some strange things going on. I still get those
> errors, and if I remove the for-loop, nothing is played.
>
> Here is my code. [1]
>
> Can someone see what's wrong?
>
> Hugs,
> Louise
>
>
> [0]
> http://www.google.com/codesearch/p?hl=en&sa=N&cd=1&ct=rc#4FSOSMZ6Pxc/distfiles/alsa-lib-1.0.14rc2.tar.bz2|ZScnKi-LryE/alsa-lib-1.0.14rc2/test/pcm_min.c&q=pcm_min.c<http://www.google.com/codesearch/p?hl=en&sa=N&cd=1&ct=rc#4FSOSMZ6Pxc/distfiles/alsa-lib-1.0.14rc2.tar.bz2%7CZScnKi-LryE/alsa-lib-1.0.14rc2/test/pcm_min.c&q=pcm_min.c>
>
> [1] http://pastebin.com/m2f28b578
>
> The correct way is to use snd_pcm_get_params() to get buffer_size and
period_size

*snd_pcm_set_params() has limitation

The most common sound card (e.g. HDA ) has the following constraints
on period bytes and buffer bytes

     snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_BUFFER_BYTES,
                                    128);
     snd_pcm_hw_constraint_step(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_BYTES,
                                   128);
*

you cannot get exactly 0.5 second period time when rate is multiple of 3 (
e.g. 48000 Hz )