[USRP-users] timed_command

Nowlan, Sean Sean.Nowlan at gtri.gatech.edu
Tue Sep 3 09:39:43 EDT 2013


>When I use set_command_time(), flow graph or USRPN210 seems to hang up. For example,
>
>...
>...
>while 1:
>...
>...
>t1 = usrp.get_time_now().get_real_secs()
>usrp.set_command_time(t1+0.02)
>usrp.set_center_freq(uhd.tune_request(f1,LO))
>usrp.clear command_time()
>....
>....
>
>flow graph/USRP doesn't run smoothly. What could be the issue? How many commands could be in a queue at a time?

My understanding is that there are only on the order of 16 slots in the command queue implemented on the USRP. Also, the commands will time out after something like 10 seconds, so you have to make your control thread sleep an appropriate amount of time so you stay within that timeout window on every command.

>One more question. Lets say current USRP time is 5.0 seconds. I give the following commands to USRP
>usrp.set_command_time(5.0+3.0)
>usrp.set_center_freq(uhd.tune_request(f1,LO))
>usrp.clear command_time()
>
>print usrp.get_time_now().get_real_secs()
>
>what would be print 5.0+something or 8.0+something? What I get from the UHD documentation is that if there is already a timed >command waiting in queue, new commands will be executed after the waiting timed command has been executed. Is that right?

I think that none of those calls block, so the time should be 5.0 + some small delay. Also I think get_time_now is independent of the timed commands and command queue.

(Somebody please correct me if I have any of this wrong!)

--sean
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