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[Discuss-gnuradio] Still not working with 2 DBSRX... :(

From: Jared Jensen
Subject: [Discuss-gnuradio] Still not working with 2 DBSRX... :(
Date: Wed, 24 Oct 2007 14:29:31 -0400

Wow.  I'm still not able to get data out of my 2nd DBSRX.  I have verified the board is good.  I modified multi-antenna/multi-fft.py to use 2 DBSRX board and the 2rx 2tx fpga build.  It works, and I can point the boards at different frequencies and see good data.  So I know the hardware is working.  Ergo, the problem is with my code, and I'm not sure what to do next.  I've debugged this ad nauseum.  I've verified that I setup r, n, gc1, gc2... all correctly.  I rebuilt usrp_standard.cc with debugging info as well as db_dbs_rx.py.  My code does the same things in setup.  I think I'm setting up each dbsrx correctly.  They return success on tune, and return successfully from all of the write_i2c commands.  I'm using I2C_ADDR 0x67 for subdev A, and I2C_ADDR 0x65 for subdev B.  I've changed those randomly and found that it correctly fails.  So I'm fairly confident that the commands are getting down to the DBSRXs.

When I call

usrp_standard_rx::make(0, decim=64, nchannels=2, mux=0x32103210, fpga_mode=0x00, fusb_block_size=0, fusb_nblocks=0, "std_2rxhb_2tx.rbf", "std.ihx")

it returns a valid usrp device, and when I query the number of channels, it says 2.  But when I do a

dev->start();  followed by
nRead = dev->read(arr, buf_size, &bOverrun); and
fwrite(arr,1,nRead, USRPfid);

I get perfect data for channel 0 (RXA) , but channel 1 (RXB) is just the noise floor.  Loading it into Matlab and looking at the fft shows RXA is doing perfectly, while RXB has no signal magnitude.  (This is when I point it at two known frequencies where both are looking at signals with good power... and even when I point them at the same frequency.)  Using ASCII art...

FFT_RXA is like....


and FFT_RXB is just....


I'm brainstorming and I wonder if I setup RXB correctly, but haven't sent some command to gate the data through.  Or if there is an additional step when using 2 channels that isn't documented.  Any ideas of things I could look at?

Like I said, gnuradio is able to talk to both boards and get good data, but my C++ code isn't.  I can only get good data from RXA.  RXB is flat.  (Well... there's low magnitude white noise, but no significant power.)

Am I missing a step?  All was well until I added a second DBSRX to the system, and now I can't get data from that new board.  <Homer Simpson> Save me Eric/Matt/anyone better at this than I!  </Homer Simpson>


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