Re: [Discuss-gnuradio] gr_crc16

[Pete Soper]

Hi Luis,
            There have been two flavors of 16 bit CRCs in use for a 
long time and you probably need to determine which of these your 
transmitter uses.
   The clue is that the "CCITT" algorithm calls for the computed CRC to 
be initialized to all ones, while for the "other" one (called "CRC16" in 
the 70s when I was implementing HDLC  the hard way)  a zero initial 
value is used.  A quick set of Googles suggests both polynomials are 
still in use.
    The other discriminator is that CCITT is called "polynomial 0x1021" 
while CRC16 is "0x8005". In other notation CCITT  is X^16 + X^12 + X^5 + 1.
      If you don't get a solution within a week, remind me by direct 
mail, as I'll be past a deadline then. Adding this to gr would be the 
right speed for my old brain if somebody hasn't already written it.

Regards,
Pete AD4L

Luis Simoes wrote:
> Hi all,
>
> I need to check payload data with only 2 crc bytes. Unfortunately my 
> transmitter sends only data with 2 crc bytes. There is only the gr_crc32 
> module in gnuradio core with an algorithm that uses a table array with 256 
> elements. I want to ask if there is someone out there who has had a similar 
> problem and implemented a gr_crc16 module? Please give me some help because I 
> don't know how was created this table and which algorithm was used? 
>
> Thanks in advance,
> Luis
>
>
>
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