On OMAP4, sending USB audio over the High Speed port typically results
in data loss (audio noise). If I modify sound/usb/urb.c to tweak things
like the "total_packs" calculation, I can sometimes get it to work well
for a specific case. How do I "right-size" the packets? Or should I be
doing something else?
DETAILS....
Platform: TI OMAP4 4460
Board: Blaze Tablet
EHCI: Onboard OMAP4, IP provided by Synopsys. Driver is
drivers/usb/host/ehci-omap.c
Audio device: Logitech H360 Headset (USB)
Kernel: TI's p-android-omap-3.0 branch[1]
Example:
If I play 2-channel, 16-bit, PCM audio at 44100 Hz, the URB completion
callback will often show that all of the data did not reach the
end-point. The audio plays, but has pops.
In this case, sound/usb/urb.c typically calculates that it wants to send
24 URB's in each transer. If I manually alter it to use 12 instead,
then the audio plays as expected.[2] However, the same tweak does not
work for 48000 Hz.
-gabriel
[1] http://omapzoom.org/?p=kernel/omap.git;a=summary
[2] Inside snd_usb_init_substream_urbs(), just before the
"allocate and initialize data urbs" loop.
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