[alsa-devel] Questions on usb audio development

[Takashi Iwai]

At Sun, 20 May 2007 15:25:31 -0400,
Lee Revell wrote:
> 
> On 5/20/07, LCID Fire <lcid-fire at gmx.net> wrote:
> > Hi.
> > I know there is quite some documentation how to develop a pci driver for
> > alsa - but since I'll try to get a usb device working I was wondering
> > how to write a usb driver? Is it just the same? How to interface the
> > various aspects of the device with regards to descriptor reading, ...
> 
> Look at the snd-usb-audio and usx2y sources.

Also the new caiaq driver.

The major difference between the normal PCI and USB audio drivers is
that USB audio has no traditional DMA like most PCI devices have.
Thus the driver has to sets up URB pakets.  usb-audio driver creates
an intermediate ring-buffer that is used for the communication from/to
user-space, and URBs are made from this buffer.


Takashi