Re: RX/TX switching

[Johannes Demel]

Hi Fabien,

do those underruns occur after you lock/unlock and switch from TX to RX 
or vice versa? Do you see overruns as well?

I'd assume the USRP expects a constant sample flow and even a short 
interuption, like your lock/unlock task interrupts that flow.
Still assuming this is the root cause, you might fix this by sending an 
EOB signal to the USRP before you lock the flowgraph.

Besides, the whole SOB/EOB mechanism might help you with your issue. You 
can just stop the TX flowgraph portion while you don't need it. By stop 
I mean, the flowgraph is not fed any new samples and just idles.
As an added bonus, you minimize LO leakage which might be an issue for 
your RX flowgraph. I know this is a more intrusive change.

Cheers
Johannes

On 04.03.22 10:45, Fabien PELLET wrote:
> Hello again,
>
> I build a flowgraph in C++ with an RX chain and a TX chain. I'm using a 
> USRP N210. When I'm in RX, the TX chain is connected to a constant zero 
> source and feed a null sink and the RX chain is connected to USRP source 
> and sink. When I'm in TX, it is the opposite.
>
> I have to keep the two chains running at the same time for switching 
> speed purpose and do not have to stop the flowgraph and restart it. So 
> for my switching, I just lock the top block and unlock it after.
>
> If I always stay in RX, I have no underrun. Same thing in TX. My problem 
> is that when I lock and unlock the flowgraph, I get a lot of underruns.
>
> As a test, I remove the TX part of my flowgraph and only keep the RX 
> part and I try do some lock/unlock sometimes : same problem with underruns.
>
> How to do lock/unlock safely in C++ to avoid underruns ?
>
> Thanks for the help,
>
> Best regards,
>
> Fabien, F4CTZ.