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Re: [Discuss-gnuradio] Buffer Overflow Debug

From: Martin Braun
Subject: Re: [Discuss-gnuradio] Buffer Overflow Debug
Date: Thu, 14 May 2015 16:05:25 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 14.05.2015 15:26, Richard Bell wrote:
> Hi all,
> I'm working on an incredibly annoying issue related to my use of the
> Header/Payload Demux (HPD) block. I think it's related to a buffer
> overflow at some point, but I'm having a really hard time coming up with
> a proper debug strategy to nail this down.
> What I'm seeing is my data streams freeze after the input to the HPD
> block, both on the header branch and the payload branch. Everything
> before the HPD block continues on without issue. The time it takes the
> streams to freeze is HIGHLY variable. I've watched it run for 30 minutes
> straight before a freeze and I've watched it freeze a few seconds after
> start. I'm using tags generated by the Correlation Estimator as the
> trigger for the HPD block.
> My question is this, if I suspect a buffer overflow is causing a freeze,
> how would I prove this to myself?


a "buffer overflow" wouldn't cause GR to freeze, rather, it would crash.
Going by your previous messages, I suspect what you're seeing is that
the HPD is starting to block, causing backpressure until that in turn
reaches the source. (Correct me if I'm wrong).

I remember you previously mentioning something similar. Did you confirm
the header parser is actually sending out a message for every data
packet it receives? This is a case where the HPD is actually designed in
a way that it'll fail.

As a debugging strategy, I would recommend printing out the state
changes inside the HPD state machine. If it freezes, it would be
interesting to see in which state that is.


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