From mboxrd@z Thu Jan  1 00:00:00 1970
From: Clemens Ladisch <clemens@ladisch.de>
Subject: Re: [PATCH] ALSA: usb: refine delay information with
 USB	frame counter
Date: Thu, 25 Aug 2011 09:54:14 +0200
Message-ID: <4E55FFA6.90506@ladisch.de>
References: <1314221197-23719-1-git-send-email-pierre-louis.bossart@linux.intel.com>
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To: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Cc: alsa-devel@alsa-project.org
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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
wrap-arounds:

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.


Regards,
Clemens