[Alsa-user] Experimental USB audio support

[Takashi I. <ti...@su...>]

Hi,

right now you can find a driver for USB audio on cvs.
it's in alsa-driver not in alsa-kernel.
the driver will be built automatically when CONFIG_USB is specified in
kernel config.

please note that this driver is EXPERIMENTAL and TENTATIVE.
my first plan was to implement a USB library layer on alsa-lib, but it
was found out that implementation of isochronous transfer via 
usbdevfs will bring some difficulty.  so i started coding of a normal
kernel driver at first.
if any feasible solution to port such a stuff into user space, we
should do that.

but anyway, it's good to have a working code.  we can move it to other
place later.


the current code is partly based on OSS/USB audio.c code, but apart
from the parsing routine of audio-streaming, the resultant codes
became fairly different from the oss code.

almost all mixer controls are supported except for graphic equalizer.
the mapping of topology might not be perfect, since alsa has a plain
control structure.

so far, i've tested only audio playback on my speaker, which is
adaptive out without pitch/freq setting.  xmms is working.
the driver accepts the period size up to 1ms.  a courageous user can
try such a heavy condition.  (me?  did not yet :)
24bit / 96kHz should work, too, but i have no such a hardware.
besides, capture is not tested at all.


if you have a usb audio device, please test once.
(oh, i forgot to mention the driver name - it's "snd-usb-audio"
 quite easy, isn't it?)

if you find somewhat strange behavior (especially in mixer controls),
please send me the output of lsusb.

btw, when you use snd-usb-audio module, please make sure that you
don't load OSS audio.o together.  hotplug likely loads both modules at
the same time.


ciao,

Takashi