[USRP-users] performance issues

Per Zetterberg perz at kth.se
Tue Nov 30 01:17:31 EST 2010

On Tue, 2010-11-30 at 00:42 -0500, Josh Blum wrote:
> > Let me clarify. I transmit frames between two usrp2+laptop at 25Msamp/s.
> > The two USRPs take turns at transmitting. Thus every other frame goes
> > into from "A->B" and the others "B->A".  I do it at regular time
> > intervals using time stamps where "time_stamp_i = i * time_inverval".
> > With the old UHD I was able to use timer_interval=6ms with the new UHD I
> > need at least time_interval=100ms. 
> > 
> > 
> There was a bug in the FPGA code where the first packet of a consecutive
> timed-burst was dropped and the subsequent packets of that burst sent
> ASAP. You may be seeing the effect of the packets being sent properly
> because as of the last image, this should not have worked.
> Since you are seeing lots of underflow, how early are you sending the
> packets to the device? Meaning, how many ms before the timestamp on the
> packet?
> -Josh

I only changed the UHD in one of the two ends of the link. I think it
was on the node that transmits in the first frame. At 100ms I am seeing
a single overrun as I can recall. At smaller time intervals it will
print out a few more and then hang. The node that transmits the first
frame will send the frame about two seconds in advance. Then it will
"issue_stream_cmd" with a "time_spec" which is set "time_interval" after
the frame was transmitted. After this frame has been received it is time
to transmit the next frame at another timer_interval later ......

Thanks for the prompt response!


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