On Sun, Sep 8, 2019 at 5:23 PM Pavel Hofman <pavhofman@xxxxxxxxx> wrote: > Hi, > Gathering data for USB async gadget feedback ( > https://mailman.alsa-project.org/pipermail/alsa-devel/2019-August/154819.html > ) requires measuring average data rate to/from a device. For testing I > added measuring/averaging code to methods snd_pcm_hw_writei, snd_pcm_hw_readi, > and snd_pcm_hw_mmap_commit in > https://github.com/alsa-project/alsa-lib/blob/master/src/pcm/pcm_hw.c . > In all cases I take the parameter "size" of all the three methods as the > number of samples written/read. > > MMAP: When mmap is used (e.g. plughw:X + sample format conversion), I get > very stable results for MMAP playback on all soundcards I have tested. But > for capture I get identical results to playback for one soundcard (PCI > Envy24), while the averaged rate calculated from "size" in > snd_pcm_hw_mmap_commit fluctuates for capture on Intel HDA. > > > I suspect the size parameter of snd_pcm_hw_mmap_commit is not the actual > amount of samples read during the MMAP capture. Please how to calculate the > number of samples read from the variables available in that method? > The mmap fluctuations seem to be fixed by using increases in hardware pointer pcm->hw.ptr values instead of frames variable. Please do these values wrap up or do they grow to max long? Still contiguous after 10 minutes of running. I see the hw.ptr gets zeroed at XRUN. If I do not check for xruns ( snd_pcm_state(snd_pcm_t *pcm)?), can I just monitor continuity of hw.ptr and restart the averaging if the new hw.ptr is lower than the previous one, or are there any quirks to watch out? Thanks a lot, Pavel. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
