* Takashi Iwai (tiwai@suse.de) wrote:

At Tue, 13 Apr 2010 10:10:02 +0200 (CEST), Jaroslav Kysela wrote:

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On Tue, 13 Apr 2010, Takashi Iwai wrote:

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At Fri, 9 Apr 2010 11:03:03 -0400, Mathieu Desnoyers wrote:

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Hi,

I was looking at snd_pcm_share_open() in alsa-lib-1.0.22, and stumbled on the following line:

    pcm->monotonic = pcm->monotonic;

what is that supposed to do ? There is clearly something wrong there.

Yeah, very fishy here.

I suppose this plugin can't handle monotonic time as is. Jaroslav, could you fix that?

The plugin can handle the monotonic clock as well. The correct line should be:

pcm->monotonic = slave->pcm->monotonic;

Ah indeed. It's a so complex code that is barely used ;)

Actually, I ran into this code because I was grepping for "monotonic" field modifications. It's indeed not run on my setup. However, what I experience is the following problem:

I instrumented the xrun() handler from aplay/aplay.c so I could study buffer underruns with the kernel trace with LTTng. Was I noticed is that the underrun error message returns a bogus underrun duration value because aplay is in "monotonic" time mode, but alsa-lib returned to non-monotonic mode (but it detects the monotonic clock upon initial setup).

Quick test code (that also forces the gettimestamp "monotonic" to 1 (locally)).

Finding out where the value is brought back to 0 might involve poking in the lib code with printf (sorry, I don't currently have the time required to do it myself).

Thanks,

Mathieu

Index: alsa-lib-1.0.22/src/pcm/pcm_hw.c =================================================================== --- alsa-lib-1.0.22.orig/src/pcm/pcm_hw.c 2010-04-09 10:33:44.000000000 -0400 +++ alsa-lib-1.0.22/src/pcm/pcm_hw.c 2010-04-09 10:43:49.000000000 -0400 @@ -1208,6 +1208,7 @@ pcm->poll_fd = fd; pcm->poll_events = info.stream == SND_PCM_STREAM_PLAYBACK ? POLLOUT : POLLIN; pcm->monotonic = monotonic; + printf("test is mono %d\n", monotonic);

ret = snd_pcm_hw_mmap_status(pcm); if (ret < 0) { Index: alsa-lib-1.0.22/src/pcm/pcm_local.h =================================================================== --- alsa-lib-1.0.22.orig/src/pcm/pcm_local.h 2010-04-09 10:31:12.000000000 -0400 +++ alsa-lib-1.0.22/src/pcm/pcm_local.h 2010-04-09 11:04:38.000000000 -0400 @@ -952,6 +952,8 @@ static inline void gettimestamp(snd_htimestamp_t *tstamp, int monotonic) { #if defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC) + printf("ismonotonic %d\n", monotonic); + monotonic = 1; if (monotonic) { clock_gettime(CLOCK_MONOTONIC, tstamp); } else { Index: alsa-lib-1.0.22/src/pcm/pcm_file.c =================================================================== --- alsa-lib-1.0.22.orig/src/pcm/pcm_file.c 2010-04-09 10:33:40.000000000 -0400 +++ alsa-lib-1.0.22/src/pcm/pcm_file.c 2010-04-09 10:45:27.000000000 -0400 @@ -785,6 +785,7 @@ #else pcm->monotonic = 0; #endif + snd_pcm_link_hw_ptr(pcm, slave); snd_pcm_link_appl_ptr(pcm, slave); *pcmp = pcm;

thanks,

Takashi