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ASM CRC

Hello All,

I have this asm crc calculation code:

            ADDCHECK   PUSH    ACC                 ;for 8031
                         ADD     A,CHEKSUM
                         RLC     A
                         JC      ADCK3
                           XRL     A,#11011101b    ;(#0DDh)
            ADCK3        MOV     CHEKSUM,A
                         CLR     C                 ;if CHK >= 244 then CHK= CHK-244
                         SUBB    A,#224            ;(#0E0h)
                         JC      ADCK4
                           MOV     CHECKSUM,A      ;<CHK> always < 224 !!!
            ADCK4      POP     ACC
                       RET
;==============================================================

            ADDCHECK:  PUSH    AX                  ;for 8086
                         ADD     AL,CHECKSUM
                         RCL     AL,1
                         JC      ADCK3
                           XOR     AL,11011101b
            ADCK3:       MOV     CHECKSUM,AL
                         SUB     AL,224
                         JC      ADCK4
                           MOV     CHECKSUM,AL
            ADCK4:     POP     AX
                       RET

I want to adapt for my current MCU C8051F340, as included asm code or "C" source code.
(I'm "C" proggramer). Can you help me?

Thank you for Attention!

0 Andy Neil over 7 years ago

Is there actually a shortage of CRC implementations in 'C' ... ?

Anyhow, here's how to create a C51 assembler module callable from 'C':

www.8052.com/.../149030
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0 Krasimir Pashov over 7 years ago in reply to Andy Neil

Hello Mr.Neil,
This is my "C" code. I think it work correct. I have no experience with 8051 assembler and especially with Silabs C8051Fxxx!

#define GET_CERRY_BIT(X) ((X >> 8) & 1)


unsigned char GetCrc(unsigned char *buffer, unsigned char bufsize) {

        unsigned char i;
   unsigned int AL;
   unsigned char checksum,temp;
   bit carry;

   if(bufsize == 0)
      return(0);

   checksum = 0;

   for(i = 0; i < bufsize; i++) {

    AL = buffer[i];

    AL+=checksum;

    if (AL & 0x100){

                        AL <<= 1;
                        AL |= 1;
                        carry = GET_CERRY_BIT(AL);
                }
    else{

                        AL <<= 1;
                        carry = GET_CERRY_BIT(AL);
                }
    if (carry==0)
       AL^=0xDD;

    temp = (unsigned char)AL;

    if (temp < 224)
       checksum = temp;
    else
       checksum = temp-224;
   }
   return checksum;
}

0 Clive Unspecified over 7 years ago in reply to Krasimir Pashov

>>I think it work correct.

Perhaps you have some example data with a sum so you can actually validate it?

Testing it against the x86 code suggests it is good

unsigned char GetCrc2(unsigned char *buffer, size_t bufsize) // sourcer32@gmail.com
{
  unsigned short checksum = 0;

  while(bufsize--)
  {
    checksum += *buffer++;

    checksum <<= 1;

    if ((checksum & 0x200) != 0) // ADD carry
      checksum |= 1;

    if ((checksum & 0x100) == 0) // RCL carry
      checksum ^= 0xDD;

    checksum &= 0xFF; // Modulo 256

    if (checksum >= 0xE0) // Modulo 224
      checksum -= 0xE0;
  }

  return((unsigned char)checksum);
}

int main(int argc, char **argv)
{
  unsigned char test1[] = { 0x01,0x02,0x03,0x04,0x05,0x06 }; // 0x4A
  unsigned char test2[] = { 0x11,0x22,0x33,0x44,0x55,0x66 }; // 0x23
  unsigned char test3[] = { 0x66,0x55,0x44,0x33,0x22,0x11 }; // 0x59

  printf("%02X\n", test(test1, sizeof(test1))); // Assembler
  printf("%02X\n", test(test2, sizeof(test2)));
  printf("%02X\n", test(test3, sizeof(test3)));
  putchar('\n');

  printf("%02X\n", GetCrc(test1, sizeof(test1))); // Yours
  printf("%02X\n", GetCrc(test2, sizeof(test2)));
  printf("%02X\n", GetCrc(test3, sizeof(test3)));
  putchar('\n');

  printf("%02X\n", GetCrc2(test1, sizeof(test1))); // Mine
  printf("%02X\n", GetCrc2(test2, sizeof(test2)));
  printf("%02X\n", GetCrc2(test3, sizeof(test3)));
  putchar('\n');

  return(1);
}