linux-kernel - Re: [PATCH v2 0/3] USB Audio Gadget refactoring

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Date:	Tue, 16 Aug 2016 11:32:55 +0200
From:	Clemens Ladisch <clemens@...isch.de>
To:	Peter Chen <hzpeterchen@...il.com>,
	Ruslan Bilovol <ruslan.bilovol@...il.com>
Cc:	Felipe Balbi <balbi@...nel.org>, Daniel Mack <zonque@...il.com>,
	Jassi Brar <jassisinghbrar@...il.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/3] USB Audio Gadget refactoring

Peter Chen wrote:
> I find UAC2 (UAC1 is ok)  support is not well with the latest mainline
> kernel w/o your patch set. The windows7 can't install the driver
> successfully

Windows does not have UAC2 support.

> and the playback shows underrun (using local codec)
> using Linux host.

> # arecord -f dat -t wav -D hw:1,0 | aplay -D hw:0,0 &

The clocks of the two devices are not synchronized.

In the ALSA API, a PCM device is assumed to have its own clock, so it is
not possible to synchronize the USB gadget to the actual sound device
without some separate mechanism (like the old uac1 gadget probably has).


Regards,
Clemens