Re: [Discuss-gnuradio] Locking USRP2 to external 10MHz reference in the UHD/GRC universe

[Josh Blum]

The locking to external ref in the uhd mimo blocks is automatic. If you 
are receiving samples, then the individual channels are aligned to their 
timestamps. Otherwise gnuradio gets a 404 samples not found.

You can also see the alignment if you look at magnitude of ch0 vs ch1 on 
a scope sink (assuming the RF input is identical). I have tested this 
with Basic RX boards; what daughterboards are you using?

-Josh

On 08/26/2010 07:40 AM, Johannes Wenzel wrote:
> Hi,
>
> I'm using a mimo (2x2) USRP2 system. Both of the receiver USRP2 receive a PPS- 
> and a Clock-Signal provided by one GPS card. In grc I use the uhd_mimo_source 
> block and two file_sink to receive and save the data sent. After starting RX 
> the USRP2 mimo system seems to lock to the reference clock and reset the timer 
> on PPS. Is this true? Or do I have to configure the block to do so? If I test 
> the data with correlation it fails, which seems to be an indicator that at 
> least the reference clock is not locked on.
>
> Is the uhd_mimo_source block automatically locked to external reference clock 
> if used or do I have to configure it?
>
> Thanks
>
>   Johannes.
>
> Am 23.08.2010 um 05:02 schrieb Josh Blum:
>
> > Swig brings in the clock config struct into python. The python code looks like:
> >
> > > > > from gnuradio import uhd
> > > > > ccfg = uhd.clock_config_t()
> > > > > ccfg.ref_source = ccfg.REF_SMA
> > > > > ccfg.pps_source = ccfg.PPS_SMA
> > > > > ccfg.pps_polarity = ccfg.PPS_POS
> >
> > so the the grc xml wrapper you need that bit of code along with
> >
> > $(id).set_clock_config(ccfg)
> >
> > -Josh
> >
> > On 08/22/2010 04:52 PM, Marcus D. Leech wrote:
> > > How do I arrange to lock the USRP2 to an external 10MHz reference in the
> > > UHD+GRC world?  Is there an "arg" I can pass when I
> > >    create the UHD USRP2 simple source in GRC?
> > >
> > > This is for some pulsar research, where an external stable reference
> > > makes life soooo much easier.