P25 CRC algorithm

[rickak]

Wondering if anyone knows, and is willing to share, the CRC calculation algorithm for P25 trunking messages. I have a program I have put together for decoding the messages but this is one thing I have not been able to figure out yet.

Thanks,
Rick

 

[mikey60]

Wondering if anyone knows, and is willing to share, the CRC calculation algorithm for P25 trunking messages. I have a program I have put together for decoding the messages but this is one thing I have not been able to figure out yet.

Thanks,
Rick

There's actually two different CRC calculations you need to do, depending on if it's a standard packet(16 bit), or an extended (aka multi-packet) packet (32 bit).

The library I'm using for this is on the web. As the person that helped me get this working suggested, do a google search for "Ross Williams" CRCModel and you should be able to find it.

Mike