Re: [Discuss-gnuradio] Multiple USRP2 sync

That would be useful for cases when your gpsdo does not have a serial
port or cannot be programmed to report a timestamp on the pps. I like
the idea; it would probably require an additional FPGA readback register
and some supporting host code.

-Josh

On 05/30/2010 07:57 AM, David Evans wrote:
> if I have two (or more) usrp2s, and I do a set_time_next_pps(), there is (or is there?) a chance
> that the pps could occur after the first call, so the second call will
> set the second usrp a second later. I would need to know when there is a pps or seconds transition prior to setup, then have one or two seconds
> to call set_time_next_pps(). Ok, I could read the system time, but I
> would need a gps with pps/ref out, and sync'd using ntpd or gpsd, and
> this may not be guaranteed. Or I could just monitor the pps level via
> the serial port (DCD, like ntpd does with nmea stream) to guarantee when the seconds tick over. If the pps state could be read back from the
> usrp (approx 80ns rtt) however, this would simplify the system and
> hardware requied (USB dongle, TTL to RS232 convertor, extra wires,
> etc...). So...
>
> while (get_pps_level() == 0); // wait for edge
> while (get_pps_level() == 1);
>
> u1->set_time_next_pps(...); // We are guaranteed at least one second to issue this to both usrp at
> once
> u2->set_time_next_pps(...);
>
> Thanks
> David
>
>
>
>
>
>
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