Calculated CRC value does not match incoming CRC value

[Ftaht.1]

Hello

I'm having trouble calculating crc. I am using STM32F401 with cube ide.

The correct crc occurs on crccalc.com. But I couldn't run CRC-8 with MCU. I have looked at the examples, but when I try it gives different results.

 

Can you provide a working code example?

[Tesla DeLorean]

Sorry, but in what context?

I don't recall the F4 provides a programmable CRC peripheral, is this under SPI? Please elaborate on the application.

[Ftaht.1]

I'm getting the data with I2C. For example, incoming data;

0x17 0X1D 0x00 0x0A

Data is: 171D00

CRC is : 0A

I must use CRC-8, http://smbus.org/faq/crc8Applet.htm

x8+x2+x+1

i don't know how to calculate this crc-8 with mcu :(

When I calculate via http://crccalc.com, input: 171D00, result is 0A (this is ok)

I couldn't get this result when I calculated it with mcu.

I tried the library here. But the result does not match

https://stm32f4-discovery.net/2015/07/hal-library-10-crc-for-stm32fxxx/

Thanks for help

[Tesla DeLorean]

>>I couldn't get this result when I calculated it with mcu.

Right because the MCU has a fixed 32-bit CRC / Polynomial implementation in hardware which is entirely unusable for your application

>>i don't know how to calculate this crc-8 with mcu

A regular software implementation would work

[Tesla DeLorean]

// CRC8 0x07 Example   sourcer32@gmail.com
 
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
 
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned long uint32_t;
 
uint8_t crc_07(uint8_t crc, uint8_t data)
{
  int i;
  crc = crc ^ data;
  for(i=0; i<8; i++)
    if (crc & 0x80) // Left shifting, MSB
      crc = (crc << 1) ^ 0x07;
    else
      crc <<= 1;
  return(crc);
}
 
uint8_t crc_07_block(uint8_t crc, int size, uint8_t *buffer)
{
  while(size--)
    crc = crc_07(crc, *buffer++);
 
  return(crc);
}
 
uint8_t crc_07_block_quick(uint8_t crc, int size, uint8_t *buffer)
{
  const static uint8_t crctbl[] = {  // 0x07 Nibble Table, sourcer32@gmail.com
    0x00,0x07,0x0E,0x09,0x1C,0x1B,0x12,0x15,
    0x38,0x3F,0x36,0x31,0x24,0x23,0x2A,0x2D };
 
  while(size--)
  {
    crc ^= *buffer++;
 
    crc = (crc << 4) ^ crctbl[(crc >> 4) & 0xF]; // Two rounds of 4-bits
    crc = (crc << 4) ^ crctbl[(crc >> 4) & 0xF];
  }
 
  return(crc);
}
 
int main(int argc, char **argv)
{
  char test1[] = "123456789";
  uint8_t test2[]= { 0x17, 0x1D, 0x00 };
 
  printf("%02X\n", crc_07_block(0x00, strlen(test1), (uint8_t *)test1));
  printf("%02X\n", crc_07_block(0x00, sizeof(test2), test2));
  putchar('\n');
 
  printf("%02X\n", crc_07_block_quick(0x00, strlen(test1), (uint8_t *)test1));
  printf("%02X\n", crc_07_block_quick(0x00, sizeof(test2), test2));
  putchar('\n');
 
  return(1);
}