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[Discuss-gnuradio] Missing Length Tag - tagged_stream_to_pdu


From: Mark Gannet
Subject: [Discuss-gnuradio] Missing Length Tag - tagged_stream_to_pdu
Date: Thu, 23 May 2019 10:25:55 -0700

Hello,

I'm encountering an error in my flowgraph that involves tag propagation when stopping/starting.  The flowgraph has a USRP connected to file meta sinks.  The USRP can be switched by the user to stream to a null sink when recording of data is not required.  When this happens, the file sinks are connected to a null source.  This is all great.

Recently, I've written some custom blocks that take the USRP output and process a subset of the samples to generate a power measurement at a specified interval (about 5 ms).  The USRP is connected to an RMS measurement block then to a stream_to_tagged_stream block then to a tagged_stream_to_pdu and finally to a socket_pdu where I output UDP packets with the measurement subset.  This part of the flowgraph needs to run all the time regardless of the record state.

This part of the flowgraph also works well when it is started initially up until the record state is changed.  When this happens, the flowgraph stops, waits, locks, changes connections between USRP and file sinks, unlocks, and starts.  A fatal error is posted: Missing required length on port 0 at item #0 <block_tagged_stream_to_pdu>: Missing length tag.

Is ther any way around this?  A hack of the tagged_stream_to_pdu block or stream_to_tagged_stream block?

Thanks,
Mark 

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