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

[Thomas Hobiger]

Hi Josh,


I understand that the mimo blocks use the external ref automatically, 
but how to get this done with the UHD Single source block? In one of the 
prior mails you mentioned some Python code together with the XML wrapper 
changes. Can you tell me explicitly where to put that code?

Regards,
  Thomas

On 08/27/2010 01:28 AM, Josh Blum wrote:
> 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.
>
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Dr. Thomas Hobiger
Space-Time Measurement Project
Space-Time Standards Group
New Generation Network Research Center
National Institute of Information and Communications Technology
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