Re: [Discuss-gnuradio] Simulateous transmission from two daughterboards

[Eric Blossom]

On Sat, Mar 11, 2006 at 07:06:34AM -0800, Angilberto Muniz Sb wrote:
> Eric, it works but theres something I dont
> understand...
> 
> No matter of what I put in the
> "self.u.set_mux(0xVVVV)"
> I always get 1st signal out to tx board A and 2nd
> signal out to tx board B.
> 
> I suppose I could switch output channels just swapping
> the mux values...
> 
> Also, according to "usrp_standard.cc" mux values
> should be "0,1,2" or "3". How come the example uses
> "a", "b", "9" and "8" ?! -- Im totally lost...

Please take a careful look at usrp_standard.h.  There are *two*
different muxes, one in the transmit path and one on the receive
path.  N.B., usrp_standard_tx vs usrp_standard_rx.  They behave differently.

Also, the tx path is bit odd since the CIC interpolators are in the
FPGA, but the digital upconverter is actually on the AD9862.  This
means that the transmit mux actually comes between the output of the
CIC interpolators and the inputs to the upconverter/DAC in the AD9862.
That does allow you to route either channel to either pair of
upconverter/dacs.  *However*, when you tune "channel 0", it tunes the
DDC on side A, even if you've got the mux mapped to swap the streams.

Using the example, if you're using the same kind of daughterboards on
each side, and you set them to have the same frequency on both sides,
you should be able to see the difference in the output using an
o'scope, when you change the transmit mux setting.  One has a single
tone, the other has two tones.

The relevant verilog code starts in usrp/fpga/top_level/usrp_std/usrp_std.v
The transmit mux is implemented on lines 157 to 164.

Eric