[Discuss-gnuradio] Re: USRP Tx Question

[Elaine Garbarine]

On 4/14/06 6:58 PM, "Eric Blossom" <address@hidden> wrote:

> 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?
> 
I suppose what I'm looking for is something straight forward and simple.
The method doesn't necessarily need to be very robust at this point.

> 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.
> 

This is actually exactly what I was afraid of. I'll spend some time with the
data sheet and see what I can find out about the phase accumulator.  Do you
know of a way to completely disable the DUC in the AD9862?  For my
application all of our communications will be occurring at baseband (for the
time being) so I don't necessarily need the DUC.

>> 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
Regards,
Elaine