Re: [Discuss-gnuradio] Async message flow control

[Tom Rondeau]

On Wed, Feb 26, 2014 at 12:00 PM, Nowlan, Sean
<address@hidden> wrote:
> How does one achieve flow control with the new style message passing API? I
> have a use case in which I'm generating packets in one flowgraph and pushing
> them through a pdu_to_tagged_stream (P2TS) block to be modulated in another
> flowgraph. I believe I'm overwhelming the P2TS block's queue because I get
> warnings about dropped messages. One hack I made was to insert a throttle
> block into the packet generating flowgraph. This helped a bit, but I have to
> guess the magic throttle rate at which I don't fill up the queue. Is there a
> way to have P2TS block when its queue is full and therefore generate
> backpressure on the upstream flowgraph?
>
>
>
> I basically have flowgraph (FG1) --> message domain --> flowgraph (FG2) -->
> USRP. FG1's flow rate is not constrained by streaming backpressure. FG2's
> flow rate is constrained by a USRP. To constrain FG1's flow rate I either
> have to use a throttle block or find a way to enforce flow control in the
> message domain.
>
>
>
> Thanks,
>
> Sean


Nope, no flow control on the message ports. Their original design was
for control and meta data messages, but we quickly realized their
capabilities with passing packets. Flow control here is one of our
identified problems that we don't have a current solution for. In
other words, if you come up with something, we'd be very interested to
hear it and will definitely work with you on it.

Tom