[alsa-devel] USB Audio questions

[Pierre-Louis Bossart]

> > Any idea on how this frame number can be read,
> 
> With usb_get_current_frame_number().

I hacked something to refine the delay information based on the USB
frame number. see attached patch. 
Two points can be improved:
- I am not sure how to convert from USB frames to ALSA frames. I used a
fixed value based what my headset supports
- Every second or so the estimate seems to be off by 96 samples, see
below. Not sure why this happens, how accurate the counter is and if
there a delay in handling retired urbs? Looks good enough though.
Thanks,
-Pierre

[10880.896486] plb-urb -- actual delay 96 estimated delay 0 
[10881.917729] plb-urb -- actual delay 48 estimated delay 0 
[10882.937948] plb-urb -- actual delay 96 estimated delay 0 
[10883.966190] plb-urb -- actual delay 96 estimated delay 0 
[10884.987425] plb-urb -- actual delay 96 estimated delay 0 
[10886.008654] plb-urb -- actual delay 96 estimated delay 0 
[10887.029931] plb-urb -- actual delay 96 estimated delay 0 
[10888.050153] plb-urb -- actual delay 96 estimated delay 0 
[10889.071375] plb-urb -- actual delay 96 estimated delay 0



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