[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

From: Josh Blum
Subject: Re: [Discuss-gnuradio] What time is it?
Date: Wed, 20 Jan 2010 09:26:27 -0800
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20100115 Shredder/3.0.2pre

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.


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).

reply via email to

[Prev in Thread] Current Thread [Next in Thread]