On Mon, Sep 9, 2019 at 7:44 PM Takashi Iwai <tiwai@xxxxxxx> wrote: > > 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. > > Could you elaborate the requirement? The description isn't clear to > me. > I need to slave EP OUT of asynchronous USB-audio gadget (i.e. device) to another (output) soundcard in the system so that adaptive resampling in the chain "USB gadget -> processing -> output soundcard" is avoided. For that I need to measure average throughput to/from alsa hw:X devices, to gather data for the feedback endpoint implemented by the gadget driver. I do not have any control over configuration of the devices, the feedback must run independently of the rest of the chain, of the applications used. In snd_pcm_hw_mmap_commit I subtract the advancement of pcm->hw.ptr from value approx. 10 seconds ago, divided by passed nanosecs measured by clock_gettime(CLOCK_MONOTONIC). For that I need the pcm->hw.ptr either to be monotonic, or I just reset the averaging if a non-monotony is detected (hw pointer in previous (n-1) call of snd_pcm_hw_mmap_commit was higher than current value). For better precision, would it make sense to update the pcm->hw.ptr with snd_pcm_avail call in that method? It may not be even possible in that method due to some locking, I really do not know. But my precision requirements are not very strict since I can average over long time (minutes) for the feedback (the clock difference is usually very small). > > You should be able to skip XRUN check by changing the stop_threshold. > Setting it to the boundary size essentially means skipping XRUN > checks. > Actually if xruns could be detected by discontinuity of the hw pointer, I would not need any other method. > In anyway, I put Pierre to Cc, as he's done some works in the past for > the accurate position reporting on HD-audio and USB-audio devices. > He can give a better hint in this regard. Thanks a lot, I very much appreciate your help. I do not know these low-level alsa details. But I will gladly learn. Pavel. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
