Re: [Discuss-gnuradio] RX Mux value with dissimilar d'cards, USRP1

[Eric Blossom]

On Tue, Oct 12, 2010 at 10:16:31AM -0400, Steven Clark wrote:
> Hi-
> 
> Is it possible to receive simultaneously from 1 WBX card, and 1 BasicRX
> card, on the same USRP1? Attempting this with GRC gives:
> "Cannot compute dual mux when mixing quadrature and non-quadrature
> subdevices"
> 
> I understand that the WBX is quadrature while the BasicRX is not, so this
> should require 3 of the 4 ADCs.
> 
> The WBX is in side A, the BasicRX is in side B, RXA slot.
> 
> ADC0 gets WBX I.
> ADC1 gets WBX Q.
> ADC2 gets BasicRX.
> ADC3 is ignored.
> 
> An RX Mux value of 0xF210F210 should accomplish what I want, but I see this
> note: "All Q's must be 0xf or none of them may be 0xf", which this violates.
> What gives? Where is this constraint coming from?
> 
> -Steven

The constraint comes from the implementation of the rx mux in the
FPGA.  It's configuration register contains a single bit that feeds
zeros to the Q input of all DDCs or not.

Details on the s/w to h/w mapping can be found in usrp_standard.cc
near line 469.

The software presents an interface that is more orthogonal than what
the fpga currently implements.

Eric