[Discuss-gnuradio] usrp2_fft.py and changing the gain

[John Orlando]

Hi all,
I've encountered an issue while running usrp2_fft.py with a dbsrx
daughterboard and I was looking for some insight as to what the cause
is (and a pointer towards a solution if one exists).

When I launch usrp2_fft.py with my dbsrx daughterboard installed, the
system comes up just fine and I see the expected spectrum displayed.
I can change frequencies all day long, and it works exactly as
expected.

However, as soon as I try to change the gain via the usrp2_fft.py GUI,
I get an 'O' character spit out on the USRP2's serial port, and the
GUI completely freezes.  I then have to do a manual exit from
the GUI window to get back to a cmd prompt, and can re-launch things from there.

Digging into the USRP2 firmware, the txrx.c main polling loop is where
the putchar('O') gets executed, and there are a few comments
indicating that this is in fact an error case.  But it isn't clear to
me what exactly is causing this.  The comments indicate that this may
be some sort of overrun condition, and there is a restart_streaming()
call to possibly deal with this issue, but it is commented out in the
current release.  I've tried it with a few different daughterboards,
and all seem to result in the same frozen GUI when I go to change the
gain.

Things I've tried (with corresponding results):
-Sometimes when I decimate the data sufficiently (say, to 32 or 64), I
can change the gain on the slider without a problem.  But not always.
-I can set the gain from the cmd line when usrp2_fft.py is launched,
and it works just fine.

Anyone else encountered this?  Any insights as to what the cause may
be?  I'd be happy to dig in and work on a resolution if somebody
points me in the right direction.

Here is my setup:
-GNU Radio git repo cloned ~4/5/2010
-USRP2 + DBSRX, plugged directly into the gigE port on a Lenovo
T400/Core 2 Duo laptop running FC12 (32-bit)...I've also tried this on
an Acer 8940 with a Core I7 running FC12 (64-bit)...same issue on both

Any help would be appreciated...thanks.

-- 
Regards,
John Orlando
CEO/System Architect
Epiq Solutions
www.epiq-solutions.com