[alsa-devel] loopback snd_pcm_writei

[Jaroslav Kysela]

Dne 01. 04. 19 v 15:51 Giuliano Zannetti - ART S.p.A. napsal(a):
> Hi,
> 
> I have the configuration in the asound.conf above.
> 
> my_plug - - > my_route - - > my_multi - - > slave0 (forward)
>                                       - - > slave1 (loopback)
> 
> I open the plug my_plug in the block mode:
> 
>     writtenFrames = snd_pcm_writei(handle, bufferToWrite, bufferToWriteSize);
> 
> The issue I see is that there are several "writes" with 0 written frames. It seems like the snd_pcm_writei does not hold until data will be written. In general, 0 written frames sounds weird to me, because snd_pcm_writei should block itself if no space is available in the circular buffer right?
> 
> I have tried to fix the following method in pcm_multi.c, as Jaroslav Kysela suggests.
> 
> -static int snd_pcm_multi_may_wait_for_avail_min(snd_pcm_t *pcm, snd_pcm_uframes_t avail ATTRIBUTE_UNUSED)
> +static int snd_pcm_multi_may_wait_for_avail_min(snd_pcm_t *pcm, snd_pcm_uframes_t avail)
> {
>         snd_pcm_multi_t *multi = pcm->private_data;
> -       snd_pcm_t *slave = multi->slaves[multi->master_slave].pcm;
> -       return snd_pcm_may_wait_for_avail_min(slave, snd_pcm_mmap_avail(slave));
> +       unsigned int i;
> +       for (i = 0; i < multi->slaves_count; ++i) {
> +               if (snd_pcm_may_wait_for_avail_min(multi->slaves[i].pcm, avail))
> +                       return 1;
> +       }
> +       return 0;
> }
> 
> But unfortunately the issue has not been resolved.

Hi,

  I did some debugging (it's pretty reproducible) and the real fixes are here:

https://git.alsa-project.org/?p=alsa-lib.git;a=commit;h=4694a6643dc09c5e41969d33ed98f42278a02d40
https://git.alsa-project.org/?p=alsa-lib.git;a=commit;h=c7fc3fdbe23e63757b0e2c88c0d7c029c660923b
https://git.alsa-project.org/?p=alsa-lib.git;a=commit;h=369df322577034ea872978d6470edbadf30d81a9
https://git.alsa-project.org/?p=alsa-lib.git;a=commit;h=0bfad420efea328a50361bb3ed11487acf69da25

  Just get the latest alsa-lib and it should work correctly now. Let me know the result.

					Thanks.
						Jaroslav

-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.