At Sat, 08 Dec 2007 15:58:40 -0500, Dave Dillow wrote: > > While working with Fernando to get the sis7019 driver working in his > buildroot setup, we kept running into a lockup of the PCM stream when > using speaker-test. aplay was fine, as was other I finally tracked it > down to a combination of uclibc not doing block reads, which led to > XRUNs, and what I thought was issue in snd_pcm_lib_write1() when trying > to fill up the tail of the PCM buffer with a large write, when there was > an intervening small write. > > As it turns out, the lockup problem may simply be in speaker-write's > sw_params settings -- it calls snd_pcm_sw_params_set_avail_min() to set > the minium write to the period size, and > snd_pcm_sw_params_set_start_threshold() to start once the buffer has > been filled. This doesn't account for odd wave file lengths and XRUNs. > > The problem arises when the wave data is not a multiple of the period > size, and you get an XRUN when there is less than buffer_size samples > remaining in the current loop. > > So for example, period size is 8192, buffer is 32768, and the wave file > has 71042 samples (Front_Left.wav for speaker-test). > > speaker-test will break that into 8 writes of 8192 samples, and one of > 5506. > > If you get a XRUN in the last 32k of the file, the PCM will be stopped, > and prepared, and we'll start loading data into again. Because we have a > tail of 5506 samples, we get to the point where the available space is > less than our minimum, and then snd_pcm_lib_write1() will wait forever > for the available space to be >= runtime->avail_min, even though the > channel is stopped. > > [snip from a trace, patch to pcm_lib.c attached] > writei size 8192 avail 32768 min 8192 xfer 1 state 2 > writei size 8192 avail 24576 min 8192 xfer 1 state 2 > writei size 5506 avail 16384 min 8192 xfer 1 state 2 > writei size 8192 avail 10878 min 8192 xfer 1 state 2 > writei size 8192 avail 2686 min 8192 xfer 1 state 2 > writei loop avail 2686 min 8192 > writei loop avail 2686 min 8192 > writei loop avail 2686 min 8192 > writei loop avail 2686 min 8192 > > > Assuming that this is desired behavior from the kernel side, then I see > three options to fix this in speaker-test: > 1) snd_pcm_sw_params_set_avail_min() to 1 sample > 2) snd_pcm_sw_params_set_start_threshold() to start when (nperiods - 1) > are ready (or be even more aggressive) > 3) call snd_pcm_drain() at the end of each loop to clear out the buffer. > This won't help if the wave file has fewer samples than the buffer size. > > Options 1 or 2 seem to be best. > > Thoughts? Just to be sure: Is it with the latest alsa-lib and alsa-utils from HG? Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
