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Re: [Xylo-SDR] Saxo
Phil Harman wrote:
get something working using the drivers that come with the Xylo board. That
is real close now. I have full duplex going at 48k 16 bit and Bill will
soon have his "Hello World" ( I/Q from an FPGA test signal giving a carrier
on the PowerSDR bandscope).
I am already facing issues with the Bulk USB mode in that if the PC gets too
busy then, although the packets arrive, they may be too late to be of use.
So far I've been able to code round that in VHDL by adding Tx and Rx FIFO's
in the FPGA.
You guys are hard at work. Just a quick comment:
Bulk transport is unuseable for real audio. Bulk guarantees 100% correct
data content transfer but does not guarantee delivery on time!
Whereas isochronous transfer does not guarantee 100% correct data
content but delivery will always be on time. Meaning that you could get
an incorrect bit delivered now and then but always on time. That is a
must for audio.
Phil, I suggest you abandon bulk transfer for audio because you will be
wasting your time. The other thing is that you will not achieve low
latency transport when you are not using the OS kernel drivers which
have been worked over pretty well by M$. usbaudio.sys has only one small
bug left the experts claim.
You should read up some on composite class, like an audio class and a
HID class in the one device. A bit more complex is the 7 in 1 USB
docking station. It has a parallel port, serial port, Mouse, KBD,
ethernet network adapter, USB hub and more. Check out some inf files to
see how they handle these things. Cypress has several examples and the
manual is very good.
One other issue that speaks for using generic drivers is that you need
to be able to sink/source audio from other applications like
soundrecorders, play back audio, spectrum analyzers other than PowerSDR etc.
We should think along the lines that any existing Windoze application
must be able to use the new USB audio device like any other soundcard.
It must show up in the device manager as 'Phil's sound' for example.
I'm not the expert that can solve all now but I have done some USB stuff
and will have to brush up some more. A group effort will succeed in the
medium term, we will get there.
Have fun! 73's Helmut