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Re: [Xylo-SDR] Generic USB Audio device (was Saxo)



Bill,
What we need is a "Composite Device", that way you can implement several different classes in the one USB device. So you can have a generic USB audio class device and a HID class to control your settings in the FX2. the OS handles the audio, your application can access the FX2 via the HID class.

The new Windows Vista OS definitely will handle all we need, but I am sure it is already possible to do 192 kHz @ 24 bits under XP now.

Driver development is a pain, unless generic Windows drivers cannot do the job its best not to get into drivers.

Eventually I intend to stream high speed audio with enough bandwidth to display a whole satellite transponder, or a SW band, and make a panorama-display on the screen. For this purpose an isochronous stream is used to update a huge buffer in user memory. No need for a generic driver here. I'm no expert (yet) but have done a few things, started with the Anchor-chip devel board. Need to refresh a few things again, hi.

More later, Helmut VK4STR


Bill Tracey wrote:
There are a number of reasons we're not trying to become a generic USB audio device. One is we're not sure if we can be a generic audio device and still get the other functions we need off the FX2 USB (control, freq correction data, etc). I agree it may be possible, but do not know enough about the USB architecture and the FX2 to say definitively one way or the other.

A second reason for not being an audio device is that historically the SDR code has had to do weird sound card specific things to deal with the different audio drivers and mixer setups. I've got somewhat of a feeling if that we keep Windows grubby hands off our precious AD data we'll be better off.

A third reason is no one knows if a generic USB audio device can do 24 bit 192 khz sampling which is one of our prime goals with the AD chips we're looking at (Wolfson, TI, and Cirrus)

Right now, I'm writing code to suck the AD data out of the USB and stuff it into PowerSDR. It is simply using the USB code from the Xylo folks and we'll see how well it works. If someone wants to go off and look into doing a generic USB audio device with the FX2 and sorting out if we can do that and still also do other control functions on the FX2 that would be terrific, if my code gets obsoleted, no problem. At the moment we do not have a lot of FX2 or USB experts on the crew, so we're seeing if we can make it work with what we know how to do at the moment.

Regards,.

Bill (kd5tfd)


At 09:08 PM 1/22/2006, Christopher T. Day wrote:

The way these things usually go, when the driver first discovers the
presence of the USB node, it asks it what it can do. The node may give
multiple answers each with a different USB Device Type. The upper level
driver then attaches a generic driver for the proper USB Device Type for
each answer; all this is supplied by the OS. From the point of view of
an application, it sees only the specific USB Device Type it is
interested in. From the point of view of the node, it has to demultiplex
the commands for the different Device Types, but that is what I thought
the on-board 8501 of the FX2 chip was for. [Anyone who knows better,
please don't hesitate to point out my ignorance.]


Chris




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