Re: Reliable "virtual RF channel" between two grc applications (UDP Source/Sink?)

[Marcus Müller]

Use zeromq; that should do just fine, and if the default TCP transport 
feels like too much overhead, you can try the ipc:// transport, iirc.

Best regards,
Marcus

On 22/04/2020 19.40, Lukas Haase wrote:
> Hi,
>
> Before going to hardware (and since my HW access is limited in Corona times) I want to build my 
> "TRX1" with a behavioral model of "TRX2" (TRX2 will eventually be a simple 
> hardware TRX on PCB, TRX1 a more signal processing heavy gnuradio application).
>
> I thought UDP Source/Sink over localhost is the way to go but this works very 
> unreliably here.
>
> For TRX1 I use (simple demo):
>
>    Signal Source (fs=5MHz, f=1MHz) --> Throttle (5MHz) --> UDP Sink 
> (127.0.0.1:1235)
>                                                         |
>                                                          \-----> |
>                                                                  | QT GUI Time 
> Sink
>                        UDP Source (127.0.0.1:1234) ------------> |
>
> For TRX2 I use (simple demo):
>
>    UDP Source (127.0.0.1:1235) --> Throttle (5MHz) --> MultiplyConst (2) --> 
> UDP Sink (127.0.0.1:1234)
>
>
> I start TRX2 first and then TRX1. Initially this simple demo worked well with 
> default values (payload_size=1500-20, sendnullpkt=false) but frequently I got 
> the following error messages (from both TRX1 and TRX2):
>
>    Too much data; dropping packet.
>
> This surprised me a lot because it's localhost which should be insanely fast. I 
> run USRP with 200 MSps (10Gbe) on the same machine without a single packet drop!
> Well, I checked the MTU of lo is not 1500 but 65536. Still baffled how this can 
> happen with a ridiculously low sampe_rate=5M, I set payload_size=65516.
> Now the error is largely gone. However, here and there I get a new nasty error 
> message:
>
>    ERROR: send error: send_to: Message too long
>
> This only seems to happen for TRX2.
> After this error I have to restart both flowgraphs.
> Unfortunately this only happens with more complicated stuff implemented within 
> TRX1/TRX2 and not reproducibly.
>
>
> Has anyone done something like this before and has a recommendation for a 
> reliable setup?
> Is UDP Source/Sink over localhost even the best way to go?
>
> Best,
> Lukas

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