At Tue, 24 Feb 2009 19:46:05 +0100, Lennart Poettering wrote: > > On Tue, 24.02.09 17:27, Takashi Iwai (tiwai@xxxxxxx) wrote: > > > > > > Moreover I can now reproduce the same issue on snd-intel8x0, albeit it > > > > > takes more than a couple of minutes to make snd_pcm_avail() return > > > > > bogus data. > > > > > > > > > > Somehow I get the feeling the problem is not so much the inaccuracy of > > > > > the pointer the kernel reports but in what alsa-libs does ith it. > > > > > > > > Hrm... both cases the pointer calculation is relatively simple, > > > > and for "hw" PCM, the avail calculation is also very straightforward. > > > > So, my first suspect is about the pointer calculation. But, of course > > > > we should check all possibilities. > > > > > > > > Can you give a small testcase? > > > > > > Ok, here's a little test case: > > > > > > http://git.0pointer.de/?p=pulseaudio.git;a=blob_plain;f=src/tests/alsa-time-test.c > > > > Finally have time to go back to this issue again now. > > > > With your test case, indeed I get abort(), too. However, checking > > through the code, you set stop_threshold to the boundary size like: > > > > r = snd_pcm_sw_params_get_boundary(swparams, &boundary); > > r = snd_pcm_sw_params_set_stop_threshold(pcm, swparams, boundary); > > > > This means essentially you are disabling the XRUN detection in the > > driver and keep it free-running. So, no wonder avail gets over > > buffer_size. It's actually an XRUN condition, but just ignored due to > > this setup. (Usually, stop_threshould == buffer_size.) > > Yes, threshold is set to boundary. But that's intended. Remember that > the original purpose of the tool is to graph _avail() and _delay() > against the time. For that I want to make sure the that timing stays > stable no matter what. > > In reality this setting should not matter at all, because most machines > should be fast enough to keep the buffer filled even if we write one > sample at a time as it is done in the example. Not really. If you feed the output to a terminal, it's damn slow. That's why I got XRUN. > The problems exposed in all the test data posted here for the various > sound cards are not normal normal buffer underruns. Well, basically "avail >= buffer_size" means the underrun per definition. The state isn't changed and kept as RUNNING just because of the stop_threshold value. > In summary: just ignore the setting of the stop threshold. It is not > related to the problems exposed here. FWIW, when I run the program and feed the output to /dev/null, I don't get abort() after minutes. It happened soon only when it runs on a terminal. So, the condition appears very likely as an XRUN. So, try to set stop_threshold to buffer_size once, and check whether you get any different result. Let's check another possibility if it really isn't the case. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
