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



Ok, I figure points 1) and 3) are pretty much the same thing - we don't
understand what USB+FX2 can really do. I've been needing the kick in the
pants to read the specs.

Point 2) is really a point in my favor, I think. All that "sound card
specific" stuff GOES AWAY if one sticks to the generic device class.
Sound card manufacturers are bound to try to distinguish their products
with super-duper proprietary gizmos that lock you into their drivers and
hardware. We just want a straightforward audio device that is simply a
whole lot better than theirs. 

Point 4) is of course the sensible thing to be doing now, but I came
across a web site somewhere that suggested that Block mode transfer is
about the worst possible mode for time-sensitive data transfer, from an
overall system point of view. [And yes, I need to verify that as well.]


	Chris - AE6VK


-----Original Message-----
From: Bill Tracey [mailto:bill@ewjt.com] 
Sent: Sunday, January 22, 2006 9:03 PM
To: Xylo-SDR Discussion; Xylo-SDR Discussion
Subject: Re: [Xylo-SDR] Generic USB Audio device (was Saxo)

1) 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.

2) 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.

3) 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)

4) 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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