Re: [Mspgcc-users] Code checksum???

[Bill Knight]

On 16 Mar 2005 21:02:07 -0000, m...@horizon.com wrote:

>Hi all,
>I want to add a sort of checksum in my F1612 to be able to verify the code
>integrity each time it is power-up. I wonder if someone has already
>experience this problem. I'd like to know few things like:

>> 1- Which algorithm you use to obtain good performance without using a too
>> big function code size

<<snip>>

Usually at startup, speed is not that much of an issue, while on an MSP,
flash & RAM space can be.  On a previous, large scale project using a
small MSP (1121, IIRC) we used a CCITT CRC calculated bit-wise for
communications packet verification.  The code follows.

Regards
-Bill Knight
R O SoftWare

uint16 calcCRC(register uint16 crc,
               register const uint8 *ptr,
               register uint16 count)

  int i;
    
  do
    {
    i = 8;
    crc = crc ^ (uint16)*ptr++ << 8;

    do
      {
      if ((int16)crc < 0)               // if (crc & 0x8000)
        crc = crc << 1 ^ 0x1021;
      else
        crc = crc << 1;
      }
    while (--i);
    }
  while (--count);

  return (crc);