On Sun, 22.02.09 04:14, Lennart Poettering (mznyfn@xxxxxxxxxxx) wrote: > I wrote this little test to track down all kinds of timer issues: it > opens and sets up a sound device. Then it will constantly query > _avail(), _delay() and _htstamp() in a busy loop writing a single > sample at a time. The three values are then printed along with a > system timestamp. The data generated like this can be opened in > gnumeric and a nice graph be drawn. Hmm, did some more testing with this tool on other cards: On es1969 snd_pcm_avail() sometimes returns values like 1073728596 samples. This smells a lot like an overflow given that this times four (i.e. the sample size in bytes) is near to 2^32. Here's an output of this tool for an emu10k1 card: http://www.nopaste.pl/9vi Check out line 4417: This is when the devcie starts playback. avail goes rightfully to 0 (i.e column 4 -- don't get confused by the line numbers the nopaste adds here), but the playback time suddenly jumps from 100113 us down to 702 us (column 4 which is the written sample counter minus the delay transformed to us). This is because in contrast to most other drivers for this one writing a sample has no direct effect on snd_pcm_delay while the device is stopped. Also this shows that the data from _avail() and _status() together is not atomic: the columns for avail delay change in different rows when we don't get scheduled often enough. Lennart -- Lennart Poettering Red Hat, Inc. lennart [at] poettering [dot] net ICQ# 11060553 http://0pointer.net/lennart/ GnuPG 0x1A015CC4 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
