[Discuss-gnuradio] header_payload_demux_impl.cc - problem when using random bit stream (variable trigger location)

[David Halls]

Hi Martin,

Making good progress with the relay but on another topic, I find if I use a random data source (rather than the 1...range in the original example) the trigger signal arrives occasionally one or two samples earlier than expected.

Say we have 96B data this gives 768/48 = 16 data symbols. Adding 3 preamble gives 19×80 samples = 1520. Sometimes there are only 1519 or 1518 samples between triggers.

This means that in the HPD code, too many items are consumed by the processing of the previous packet and thus the next trigger = 1 item is consumed in error so it is never found.

A simple hack is to consume 'x' fewer samples in the HPD code I.e. In the line

consume_each (d_header_len * (d_items_per_symbol + d_gi));

And the equivalent in the payload case, we can append ' - 3'
A slightly more robust way would be to check where the next trigger occurs and remove the corresponding number of times.

Are you able to recreate this issue? I realise that the problem only occurs when using a different data source than the standard demo, so of course it's not a bug as such at all.

Many thanks,

David

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