[Discuss-gnuradio] usrp initialization

[Hans Glitsch]

Hi,

Please help me figure out the strange problem I'm having.

In my system, the software is receiving four interleaved streams of complex 
data from the usrp.  I am trying to receive two channels on each input of 
the usrp, so I setup the usrp to ddc the center of the two channels down to 
zero frequency and then (in gnuradio) I seperate the channels by doing 
another ddc to bring each channel to zero hz and then a low pass filter. 
The second channel requires a conjugation before the ddc to flip it to the 
positive side of the freq spectrum.

I'm getting a strange behavior only on RX1 (input A of the Basic RX in 
position1 of the usrp).  If I input a signal only on channel 1, to all four 
usrp inputs it bleeds over to channel 2 at about 60% amplitude only on RX1. 
The same thing happens if I input a signal only on channel 2 -- it bleeds 
over about 60% to channel 1.

This behavior does not happen on the other three receivers at all and 
continues to present itself only on RX1 even if I swap the cables providing 
signals to the four usrp inputs.  I have even tried swapping the usrp, both 
basic RX boards, and the cables inside the usrp enclosure.  The problem 
always stays with RX1.  I know the problem is somewhere in the usrp, the way 
I initialize the usrp, or in my software.

I don't think the problem is in my software because I simply use four 
instances of the same code to process all four inputs.  But I'm not sure 
yet.

I'm using the following python to initialize the usrp, then I pass the usrp 
to c++ code via sm.Run_SM1680(adc._u).

Please tell me if you see anything wrong with this.

Thanks,
Hans

#!/usr/bin/env python
from gnuradio import usrp, gru
from gnuradio import sm
def main():
 nchan = 4
 adc = usrp.source_c(0, 250, fpga_filename="std_4rx_0tx.rbf")
 if not adc.set_nchannels(nchan):
   sys.stderr.write('set_nchannels(%d) failed to set number of channels\n' 
% (nchan,))
   raise SystemExit
 adc._write_oe( 0, 0xffff, 0xffff )
 adc.write_io( 0, 0xfff7, 0xffff )
 gain = 0
 subdev = adc.db[0] + adc.db[1]
 subdev[0].set_gain(gain)
 subdev[1].set_gain(gain)
 adc.set_mux(gru.hexint(0xf3f2f1f0))
 target_freq = sm.Get_Center()
 for i in range(len(subdev)):
   r = usrp.tune(adc, i, subdev[i], target_freq)
   if not r:
     print "set_freq: failed to set subdev[%d] freq to %f" % (i, 
target_freq)
       raise SystemExit
 sm.Run_SM1680(adc._u)

if __name__ == "__main__":
 main()