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[Discuss-gnuradio] Question


From: Ulf Lindgren A
Subject: [Discuss-gnuradio] Question
Date: Wed, 17 Sep 2008 08:38:55 +0200

Hi,
a week a goo I asked if someone could please explain how the Rx MUX is to be set, unfortunately I have not had any luck with an answer. I have read the USRP FAQ but I find the answer unclear, e.g. because I do not know the mapping of ADC number to side. In addition it is also unclear, to me, if the answer talks about a single bit position or a binary number (here several bits):

From the FAQ:

1: For example the I-data ADC is controlled by a 4-bit field: does that mean 0=0001 1=0010 2=0100 3=1000, or does it mean 0=0000 1=0001 2=0010 3=0011?

2: Which ADC is connected to which side of the USRP is 0,1 on side A?
3: How do I assign ADCs to Rx vs Rx2? 
4: Does the following text imply that all Q=0 as the standard setting?: For most real sampling applications, the Q input of each DDC is constant zero. "So quite often we don't need to modify the standard configuration of the FPGA. Actually it is anticipated that the majority of USRP users will never need to use anything other than the standard FPGA configuration."

I kindly ask some more knowledgeable to answer my question
/Ulf
My original Question
I have been trying to understand how to make an application where I use two USRPs one acting as TX and the other as RX. Both the USRP have two RFX2400 daughter boards so I would like to transmit two streams and receive two streams. My starting point was the "fm_tx_2_daughterboards.py" which I think I understand.

First question (Tx):
-The tx_mux setting for the top_block in "fm_tx_2_daughterboards.py" is 0xBA98 which is understandable. If I use
MuxVal=usrp.determine_tx_mux_value(self.u,(1,0))+usrp.determine_tx_mux_value(self.u,(0,0))
I get 0x9898 which I do not understand.
Then I wanted to write a corresponding rx_2 and I started with the mux from the description of the rx mux, here I don't know which ADC is on RxA and RxB so I cannot figure out the appropriate setting.

In case I use
MuxVal=usrp.determine_rx_mux_value(self.u,(0,0))+usrp.determine_rx_mux_value(self.u,(1,0));
I get 0x24, which kind of odd ? If I do
usrp.determine_rx_mux_value(self.u,(0,1))
I get an error (I thought this meant side A Rx2)
I guess I'm all confused and don't understand the documentation, can someone please explain the Rx mux and the automatic setting?

/Ulf


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