Results of my latest debug: dmix is reporting an error in routine snd_pcm_dmix_sync_ptr() complaining that the pipe is
in the running state.  Here is a snippet of code:

	if (avail >= pcm->stop_threshold) {
		struct timeval tv;
		snd_timer_stop(dmix->timer);
		gettimeofday(&tv, 0);
		dmix->trigger_tstamp.tv_sec = tv.tv_sec;
		dmix->trigger_tstamp.tv_nsec = tv.tv_usec * 1000L;
		if (dmix->state == SND_PCM_STATE_RUNNING) {
			dmix->state = SND_PCM_STATE_XRUN;
                 printf("%16s:%4i:(%32s): -EPIPE error.\n\n", __FILE__, __LINE__, __FUNCTION__ );
			return -EPIPE;
		}
		dmix->state = SND_PCM_STATE_SETUP;
		/* clear queue to remove pending poll events */
		snd_pcm_direct_clear_timer_queue(dmix);
	}

    Any suggestions how to fix this?  This is with version 1.0.11.  Attached is my version of pcm_dmix.c with debug
statements added, in case you want to line up the debug statements with their line numbers from the below output.

~ # aplay content/pcm48khz_2ch_stereo.wav
        pcm_dmix.c: 914:(               snd_pcm_dmix_open): first_instance 1
        pcm_dmix.c: 977:(               snd_pcm_dmix_open)
Playing WAVE 'content/pcm48khz_2ch_stereo.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
        pcm_dmix.c: 510:(            snd_pcm_dmix_prepare)
      pcm_direct.c:1177:( snd_pcm_direct_set_timer_params)
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 4000, *pcm->hw.ptr 0, *pcm->appl.ptr 0
        pcm_mmap.c: 116:(        snd_pcm_mmap_write_areas): offset 0, size 2000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 4000, *pcm->hw.ptr 0, *pcm->appl.ptr 0
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 4000, *pcm->hw.ptr 0, *pcm->appl.ptr 0
             pcm.c:2701:(              snd_pcm_areas_copy): dst_offset 0, src_offset 0, channels 2, frames 2000, format 2
             pcm.c:2570:(               snd_pcm_area_copy): bytes 8000
             pcm.c:6357:(             snd_pcm_mmap_commit): offset 0, frames 2000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 4000, *pcm->hw.ptr 0, *pcm->appl.ptr 0
        pcm_dmix.c: 727:(        snd_pcm_dmix_mmap_commit): size 2000 state 2
        pcm_mmap.c:  78:(       snd_pcm_mmap_appl_forward): appl_ptr 0, frames 2000, appl_ptr 2000
        pcm_dmix.c: 746:(        snd_pcm_dmix_mmap_commit): size 2000 state 2
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 2000, *pcm->hw.ptr 0, *pcm->appl.ptr 2000
        pcm_mmap.c: 116:(        snd_pcm_mmap_write_areas): offset 0, size 2000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 2000, *pcm->hw.ptr 0, *pcm->appl.ptr 2000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 2000, *pcm->hw.ptr 0, *pcm->appl.ptr 2000
             pcm.c:2701:(              snd_pcm_areas_copy): dst_offset 2000, src_offset 0, channels 2, frames 2000
             pcm.c:2570:(               snd_pcm_area_copy): bytes 8000
             pcm.c:6357:(             snd_pcm_mmap_commit): offset 2000, frames 2000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 2000, *pcm->hw.ptr 0, *pcm->appl.ptr 2000
        pcm_dmix.c: 727:(        snd_pcm_dmix_mmap_commit): size 2000 state 2
        pcm_mmap.c:  78:(       snd_pcm_mmap_appl_forward): appl_ptr 2000, frames 2000, appl_ptr 4000
        pcm_dmix.c: 746:(        snd_pcm_dmix_mmap_commit): size 2000 state 2
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail    0, *pcm->hw.ptr 0, *pcm->appl.ptr 4000
       pcm_local.h: 341:(  snd_pcm_mmap_playback_hw_avail): avail 4000
        pcm_dmix.c: 569:(              snd_pcm_dmix_start): state 2, avail 4000
        pcm_dmix.c: 545:(        snd_pcm_dmix_start_timer): old state 2, new 3
        pcm_dmix.c: 279:(          snd_pcm_dmix_sync_area): size 4000, state 3
        pcm_dmix.c: 314:(          snd_pcm_dmix_sync_area): state 3
        pcm_dmix.c: 584:(              snd_pcm_dmix_start): dmix->state 3
        pcm_dmix.c: 486:(             snd_pcm_dmix_hwsync): dmix->state 3
        pcm_dmix.c: 361:(           snd_pcm_dmix_sync_ptr): diff 0, dmix->slowptr 0
        pcm_dmix.c: 361:(           snd_pcm_dmix_sync_ptr): diff 0, dmix->slowptr 0
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail    0, *pcm->hw.ptr 0, *pcm->appl.ptr 4000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail    0, *pcm->hw.ptr 0, *pcm->appl.ptr 4000
        pcm_dmix.c: 279:(          snd_pcm_dmix_sync_area): size 0, state 3
        pcm_dmix.c: 361:(           snd_pcm_dmix_sync_ptr): diff 0, dmix->slowptr 0
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail    0, *pcm->hw.ptr 0, *pcm->appl.ptr 4000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail    0, *pcm->hw.ptr 0, *pcm->appl.ptr 4000
        pcm_dmix.c: 279:(          snd_pcm_dmix_sync_area): size 0, state 3
        pcm_dmix.c: 361:(           snd_pcm_dmix_sync_ptr): diff 4000, dmix->slowptr 0
        pcm_dmix.c: 378:(           snd_pcm_dmix_sync_ptr): pcm->stop_threshold 4000,  pcm->boundary 40000000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 4000, *pcm->hw.ptr 4000, *pcm->appl.ptr 4000
        pcm_dmix.c: 394:(           snd_pcm_dmix_sync_ptr): -EPIPE error.

       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 4000, *pcm->hw.ptr 4000, *pcm->appl.ptr 4000
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 4000, *pcm->hw.ptr 4000, *pcm->appl.ptr 4000
        pcm_dmix.c: 486:(             snd_pcm_dmix_hwsync): dmix->state 4
        pcm_dmix.c: 433:(             snd_pcm_dmix_status)
       pcm_local.h: 309:(     snd_pcm_mmap_playback_avail): avail 4000, *pcm->hw.ptr 4000, *pcm->appl.ptr 4000
        pcm_dmix.c: 451:(             snd_pcm_dmix_status): avail 4000
underrun!!! (at least 1.032 ms long)


Daniel Cardenas wrote:
> Takashi Iwai wrote:
>> At Thu, 8 Feb 2007 10:44:10 -0800,
>> <daniel.car@cox.net> wrote:
>>> Hi,
>>>
>>> I'm working on an unannounced SOC audio driver on an ARM system.
>>> I have a problem were audio works fine with out dmix, but when I try 
>>> to use dmix, no audio data gets to the driver.
>>> The dmix plug-in does work when attaching external usb audio device.  
>>> Trying to use dmix so that more then one application can generate 
>>> audio simultaneously.
>>>
>>> If I try with version 1.0.11 of ALSA the audio driver doesn't receive 
>>> any data after the snd_pcm_period_elapsed() function call.
> 
> Actually it is before or after.
> 
>>
>> So, actually it's a problem of driver / alsa-lib hw layer rather than
>> dmix?  You can get more verbose messages by setting LIBASOUND_DEBUG
>> variable.  See alsa-lib/NOTES for details.
> 
> I set the environment variable and I did not see additional output.  For 
> version
> 
> 
>>
>>> Here is how the driver is set up:
>>> static snd_pcm_hardware_t snd_oloriver_playback_hw = {
>>>  .info = (SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_INTERLEAVED |
>>>        SNDRV_PCM_INFO_MMAP_VALID),
>>>  .formats         = SNDRV_PCM_FMTBIT_S16_LE,
>>>   .rates         = SNDRV_PCM_RATE_48000,
>>>   .rate_min        = 48000,   .rate_max        = 48000,
>>>   .channels_min     = 2,
>>>   .channels_max     = 2,
>>>   .buffer_bytes_max = 65536,
>>>   .period_bytes_min = 32768,
>>>   .period_bytes_max = 32768,
>>>   .periods_min         = 2,
>>>   .periods_max         = 2,
>>
>> My rough guess is that the buffer and period size constraints are too
>> restrictive.  You can try to pass the exact period/buffer sizes to
>> aplay via --period-size=8192 --buffer-size=16384 options.
>>
>> Takashi
> 

Thanks,
Daniel