Re: [Discuss-gnuradio] USRP and USB full speed (1.1) transmit

[John Gilmore]

> Well, it looks like data is coming out, but it looks like I get 64
> bytes out, then there is a "hiccup" about 5 microseconds long. I am
> getting suspicious the OSK doesn't get the data on the USB bus fast
> enough. 

What is the source of the data you're transferring over the bus?  If
it is coming faster than USB1.1 can handle, of course you'll see
"hiccups" where data is dropped.  (The USB2 firmware/fpga sets a flag
that the software can read when this happens -- that's what produces
those "U" dribbles on the terminal sometimes.)

I think there's a way to select a counter in the FPGA that just
transfers an incrementing number in each outgoing USB packet.
(Perhaps it's a different FPGA load instead of a settable
flag in the main version.)  This was used to debug similar issues 
between the FPGA and the FX2, and between the FX2 and the software
library.

Alternatively, you can decimate the source down to a very low data
rate, so it won't overflow.  Get the rate as low as you possibly can,
for debugging.  (Or, if there's a demodulator in the FPGA, you could
e.g. have it tune an FM radio station, demodulate it on-chip, and
transfer only the audio over the USB bus, which would be well within
its available bandwidth.  But I don't think anybody has coded that
FPGA transform... yet.)

        John