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Re: [Discuss-gnuradio] ADC to DDC mux value, measure SNR/SNIR

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] ADC to DDC mux value, measure SNR/SNIR
Date: Thu, 29 Mar 2007 13:45:13 -0700
User-agent: Mutt/1.5.9i

On Thu, Mar 29, 2007 at 01:10:58PM -0700, Candy Yiu wrote:
> Hi,
> I am trying to do beamforming using 2 RFX 2400 boards. I am facing an 
> issue with setting the mux value (to set ADC connection to DDC and/or 
> DUC connection to DAC) on transmitter and receiver side. On the 
> transmitter side I am using the value 0xba98 and I think this works. On 
> the receiver side I have used values like: 0xf3f2f1f0 (which didn't 
> work), 0xf0f0f1f0,  0x00001100 and a few other values (which also didn't 
> work).

The RFX-2400 does uses quadrature downconversion.
To access two boards simultaneosly you want the to set the mux value
to 0x32103210.  The top 16-bits are don't care, as long as the Q
fields are not 0xf.

   * \brief Set input mux configuration.
   * This determines which ADC (or constant zero) is connected to 
   * each DDC input.  There are 4 DDCs.  Each has two inputs.
   * <pre>
   * Mux value:
   *    3                   2                   1                       
   *  1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
   * +-------+-------+-------+-------+-------+-------+-------+-------+
   * |   Q3  |   I3  |   Q2  |   I2  |   Q1  |   I1  |   Q0  |   I0  |
   * +-------+-------+-------+-------+-------+-------+-------+-------+
   * Each 4-bit I field is either 0,1,2,3
   * Each 4-bit Q field is either 0,1,2,3 or 0xf (input is const zero)
   * All Q's must be 0xf or none of them may be 0xf
   * </pre>
  bool set_mux  (int mux);

You'll also need to set_nchannels to 2.

> (0, 1) or (1,1) value for (side, subdev) is giving an error saying that 
> this tuple is out of range. value (0,0) and (1,0) only has to be set on 
> both transmit and receive side. My understanding was subdev=0 would 
> physically map to one of the antennas on the daughterboard and subdev=1 
> maps to the other antenna. My understanding is surely wrong and I am 
> missing something, can anyone pls help me understand this? 

If you're using both daughterboards simultaneously, then the rx subdev
stuff isn't going to help you out.  You need to specify the mux value
by hand.

gnuradio-examples/python/multi-antenna/multi_file.py is similar to
what you are trying to do, though it handles 4 channels using two
Basic Rx daughterboards.  The mux setting is different in that case
since it's presenting four real signals to 4 DDCs, not 2 quadrature
signals to 2 DDCs as in the case with the RFX-* boards.

N.B., you'll want to use the standard fpga image (which includes
half-band filters), not the "std_4rx_0tx.rbf" file used in the
4-channel examples.


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