Re: [Discuss-gnuradio] Expected behavior during underruns

[Thomas Tsou]

On Thu, Dec 9, 2010 at 5:11 AM, Patrik Eliardsson
<address@hidden> wrote:
> Dear list,
>
> What is the expected behavior when we get underruns with the UHD and the flow 
> control using the USRP2?
>
> 1) When we get underruns, does the usrp2 send some random samples until the 
> host computer manage to feed the usrp2 and then starts to consume the 'old' 
> samples from the host computer?
>
> Or
>
> 2) When we get underruns, does the usrp2 send some random samples while 
> throwing away old samples until the host computer manage to feed the usrp2 
> with samples to be sent in the future?
>
> Or does it work in another way?

Based on my observations with a scope, there is no output during
underruns; the usrp2 never sends random samples. Also, the usrp2
doesn't drop samples, so late samples will transmit immediately upon
late arrival. My applications deal with continuous streaming, which
requires occasionally dropping samples to maintain synchronization,
and that occurs on the host.

I should note that most of my testing was before host based flow
control was merged. I haven't noticed any significant changes
afterwards, so I assume that the underrun behaviour is unchanged.

  Thomas