[Discuss-gnuradio] Re: USRP Tx Question

[Eric Blossom]

On Fri, Apr 14, 2006 at 12:18:47PM -0400, Elaine Garbarine wrote:
> Eric,
> 
> I'm not sure how relevant my questions would be so I decided to take this
> off list.  

Very relevant.  I've cc'd the list on this reply.

> I have a USRP configuration with one USRP acting as master and the other
> acting as slave (from Martin DvH's wonderful multi-usrp code).  Martin's
> code provides for receive synchronization but not transmit sync.  I wanted
> to implement a very simple, barebones method to provide some measure of
> transmit sync.  What I was thinking of doing is simply to have the master
> FPGA output a "1" on one of the daughterboard header pins right before it
> transmits and then have the slave FPGA see that bit and transmit.

What do you mean by a barebones method of transmit sync?

On problem that will need some thinking about is that we're using the
DUC in the AD9862 and we don't have a way to reset it's phase
accumulator short of cycling power.  If you need phase coherence on
Tx, you may have to implement the DUC in the FPGA.  I'm not absolutely
certain about this, but that's my suspicion.  I suggest spending some
time with the AD9862 data sheet.

> My question for you is where in the FPGA code would be the best place to put
> this?  Should I work it into master_control or does it really belong
> somewhere else?
> 
> My other question is what might be the easiest way to have the USRP output a
> pulse on a daughtercard header pin?
> 
> I hope that my questions were at the very least coherent.  Thanks in advance
> for any help you can provide?
> 
> Regards,
> Elaine

Eric