[alsa-devel] [PATCH] ALSA: usb: refine delay information with USB frame counter

Clemens Ladisch clemens at ladisch.de
Thu Aug 25 09:54:14 CEST 2011

Pierre-Louis Bossart wrote:
> This patch relies on the USB frame counter ...

> +	if (frame_diff < 0)
> +		frame_diff += 1024; /* handle 10-bit wrap-around */

After reading through some HCD source files, I deduced the following

EHCI: 8-10 bits (default 9)
FHCI: 11 bits
IMX21: 16 bits
ISP1760: 10 bits
OHCI: 16 bits
OXU210HP: 10 bits
R8A66597: 10 bits
SL811: 5 bits(!?)
UHCI: 32 bits
xHCI: ?

So which hardware did you test this on?  :-)

As long as there isn't an API that tells us about the valid range of the
frame counter, we should probably mask off all except the lowest few bits.


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