Re: [Discuss-gnuradio] What time is it?

[Josh Blum]

I dont know what kind of delay exists been calling set_time and usrp2 
actually latching in the new times. The only way to get it exactly right 
is to use a GPS. However, for syncing the host system time to the usrp2, 
the demo could be improved with a estimate_rtt routine that times the 
operation of set_time a few times, averages the result, and uses the RTT 
to make the final call to set_time with curr_time + RTT/2.

That should get it closer, but I should note that the computer clock 
will drift and so will the usrp2 without a 10mhz reference. You may have 
to make periodic calls to set_time to keep the sub-second precision as 
accurate as possible.

-josh

> >
> Exciting! I'll take a look. Out of curiosity, do you have any sense of
> what sort of sub-second precision you're getting on setting the usrp2
> time according to the host? It looks like the sample is fairly simple,
> (i.e. just getting the current system time, then turning around and
> setting the USRP2 time ASAP to that time, taking into account the fpga
> clock rate). I wonder if the sync between host and USRP2 wouldn't be
> better improved by measuring the (rough) RTT, and taking that into
> account (e.g. measuring current system time, sending a control message
> to the USRP2 and getting a response, measuring the system time again,
> and using the difference as the RTT).
> Doug