Would crc16 be good enough? If you put the internal vars as registers and if it is small enough, make sure the target data is in cashe it should be really quick.

We use a basic CRC check on the Blackfin.  To send a N word array, we add on a single 32-bit so that when everything is xor'ed together, you end up with zero.  This is good for catching any single word error.  It's fast as well.  The code snippet is:

{

     DWORD crc=0;

     for(i=0; i<nLen; i++)

          {

          crc^=g_PacketBuffer[i];

          }

     if (crc != 0)

          goto Packet_Error;

}

Just ran into something in the Blackfin Programming Reference, remembered this thread and decided it might be worth bringing it up. There's a couple of instructions, BXOR and BXORSHIFT, which have a Type I CRC as an example of their usage. You would need to make a couple of adjustments (CRC_LEN would have to be 32, and you'd have to alter the code to be callable from C - receiving a ptr to the message as a parameter etc), however it might at the very least give you ideas. I've copied the text from the PRM below:

The code above, from Sean's post, is similar to the article Yosi pointed to earlier. In the article one can find detailed explanation on how to adjust this kind of code to specific needs.

Heh, I should really have looked at the embedded.com article you posted as it's pretty much the same as the PRM text.

Hi Yaniv,

WIth LUT, it could work like this -

/* algorithm:

   new CRC (updated each incoming byte) = (old CRC << 8) ^ (CRC_update_table[input byte ^ MSByte of old CRC] )

*/

// ... proper loading the loop, then:

// CRC lives in R0

CRC32Start:
  
   r3 = r2 << 2      || r6 = [p1];    // r6 is 32-bit CRC corresponding to input byte^MSbyte of CRC
   r3 = r7 + r3 (ns) || r1 = b[p0++]; // r7 - base  for CRC update table, r1 - input byte
   p1 = r3;                           // ptr into CRC update table, size 256*4 bytes
  
   r5 = r0 >> 24;  // 8 MSB of CRC interacting with input
   r2 = r1 ^ r5;
  
   r5 = r0 << 8;  // 24 LSB of old CRC interacting with CRC update         
CRC32End:  
   r0 = r5 ^ r6;   
  
   // 7 cycles per 8 bits = 0.875 c/bit

boris.liberol@analog.com