[Discuss-gnuradio] Question on accessing ADC I/Q outputs on RFX2400 debug headers

[Nikhil]

Hello,

I would like access to the I and Q output data (12 bits each) from ADC U601 using the debug headers from two RFX2400 daughterboards and was wondering if someone could assist my understanding and tell me if what I am doing is right or wrong prior to my actually implementing this on the USRP.  Specific questions are labelled with a "Q" in what follows.

Based on a couple of mailing list discussions I was able to figure out the following. Output enable all the general purpose i/o pins referred to below:

* Each d'board has 16-bits of general purpose i/o.

* Setting the bit makes it an output from the FPGA to the d'board.

* This register is initialized based on a value stored in the

* d'board EEPROM. In general, you shouldn't be using this routine

* without a very good reason. Using this method incorrectly will

* kill your USRP motherboard and/or daughterboard.

*/

bool _write_oe (int which_dboard, int value, int mask);

u = usrp.sink_c(0, 64)
  side0 = 0  # side A
  u._write_oe(side0, 0xffff, 0xffff)     # set all i/o pins as outputs
side1=1  # side B
  u._write_oe(side1, 0xffff, 0xffff)     # set all i/o pins as outputs
Next output enable the debug pins and enable them as debug outputs.  
  u._write_fpga_reg(FR_DEBUG_EN, ??)  <-- Q. I am not sure how to safely 
output enable the debug outputs.  Would 0xf do the job?

Q. I am also not sure how to assign the 12 I bits and the 12 Q bits from U601 across 
the daughterboard headers. Would the following in usrp_std.v (master_control) do the trick?
.debug_0(rx_a_a[11:4]),.debug_1(rx_a_a[3:0]),       
.debug_2(rx_b_a[11:4]),.debug_3(rx_b_a[3:0]),
       );

Q. I was a little confused about the "RX Nets" beside J24 and "TX Nets" beside J101 in the 
2400 receiver and transmitter schematics, respectively.  Can someone please explain?  

Thanks very much in advance!

-Nikhil