# FEC GnuRadio 3.7.8rc1 Error

**URL:** <https://www.ruby-forum.com/t/fec-gnuradio-3-7-8rc1-error/242884>\
**Category:** GNU Radio\
**Created:** [August 5, 2015, 8:08am UTC](https://www.ruby-forum.com/t/fec-gnuradio-3-7-8rc1-error/242884 "2015-08-05T08:08:38Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Sadaf\_N](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/858c86/32.png) [@Sadaf\_N](https://www.ruby-forum.com/u/Sadaf_N)\
**Post date:** [August 5, 2015, 8:08am UTC](https://www.ruby-forum.com/t/fec-gnuradio-3-7-8rc1-error/242884/1 "2015-08-05T08:08:38Z")

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Ubuntu 14.04 64-bit  
Gnuradio 3.7.8rc1

I am running this flowgraph “fecapi\_async\_to\_stream.grc” that comes with  
gr-fec. After running for a while following error always show up

…  
…  
DEBUG: 16384, 560, 272  
DEBUG: 16384, 560, 272  
FATAL: Missing a required length tag on port 0 at item #14965440  
thread[thread-per-block[7]: \<block fec\_tagged\_decoder (7)\>]: Missing  
length  
tag.

The only thing that changes is the item#.  
Testing further …

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**Author:** ![bob\_wole](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/b4bc9f/32.png) [@bob\_wole](https://www.ruby-forum.com/u/bob_wole)\
**Post date:** [August 5, 2015, 9:45pm UTC](https://www.ruby-forum.com/t/fec-gnuradio-3-7-8rc1-error/242884/2 "2015-08-05T21:45:19Z")

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On Wed, Aug 5, 2015 at 2:07 AM, bob wole [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> DEBUG: 16384, 560, 272

Bob,

You led us down a buggy path on that one. This, I’m pretty sure, is  
related  
to Richard B.'s problem for a few weeks ago where adding a time sink  
caused problems in his data stream. I have to say, I kind of dismissed  
that  
as impossible, but nope, it’s a real problem.

The problem isn’t with the GUI sinks; you can replace them with null  
sinks  
and you get the same problem. It’s a race condition in our tag pruning  
method that was changed in 3.7.6. We have a patch that we’re putting in  
now  
that will be part of 3.7.8.

The patch goes backwards a bit to how tag pruning was originally done.  
However, with the map, we no longer have to restart the iterator at  
begin()  
like we used to, and we can terminate early, so this should still be  
much  
faster than the original.

Tom