# Correlate\_access\_code\_tag\_bb gives Assertion \`px != 0' failed

**URL:** <https://www.ruby-forum.com/t/correlate-access-code-tag-bb-gives-assertion-px-0-failed/229999>\
**Category:** GNU Radio\
**Created:** [May 26, 2014, 4:32pm UTC](https://www.ruby-forum.com/t/correlate-access-code-tag-bb-gives-assertion-px-0-failed/229999 "2014-05-26T16:32:18Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![jason\_sam](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/7993a0/32.png) [@jason\_sam](https://www.ruby-forum.com/u/jason_sam)\
**Post date:** [May 26, 2014, 4:32pm UTC](https://www.ruby-forum.com/t/correlate-access-code-tag-bb-gives-assertion-px-0-failed/229999/1 "2014-05-26T16:32:18Z")

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Hi All,

I am trying to sync to a access code for a bit stream to determine the  
start of a packet and pack bits to a byte from that point. I have  
challenges getting correlate\_access\_code\_tag\_bb working. Attached is a  
test grc and every time I try to run it, it gives out  
“/target/include/boost/smart\_ptr/intrusive\_ptr.hpp:162: T\*  
boost::intrusive\_ptr::operator-\>() const [with T = pmt::pmt\_base]:  
Assertion `px != 0’ failed” at the point it matches the access code. Any  
idea why.

Also is there a better way to start packing bits to a byte at the packet  
start boundary

Thanks