Using POLY for calculating CRC of READ_ONLY space

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Using POLY for calculating CRC of READ_ONLY space

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markiscarabas
Contributor I
Hi,
Please let me know if there are known bugs in this area. I crated the array of const chars {6,3,0xb, 0xb9,00,01}  @ 0xFD00 and used POLY 0xA001.. the generated result is 0xABA7 which I think is incorrect!?
 
CHECKSUM
CHECKSUM_ENTRY
METHOD_CRC16 INIT 0xFFFF POLY 0xA001 OF READ_ONLY 0xFD00 TO 0xFD05 INTO READ_ONLY 0xF800 SIZE 2
UNDEFINED 0xFF
END
END
 
I think the correct answer is 0x7c56: see VC code below:
 
#include "stdafx.h"

int crcbuf( int crc,  int len, char *buf);
const  int crctab[] = /* CRC lookup table */
{
 0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
 0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
 0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
 0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
 0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
 0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
 0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
 0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
 0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
 0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
 0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
 0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
 0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
 0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
 0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
 0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
 0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
 0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
 0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
 0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
 0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
 0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
 0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
 0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
 0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
 0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
 0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
 0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
 0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
 0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
 0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
 0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040
};
/*
 * Update a CRC check on the given buffer.
 */
char my_array[] = {6,3,0xb, 0xb9,00,01};
int main(int argc, char* argv[])
{
 int crc;
 crc = crcbuf(0xFFFF, sizeof(my_array), my_array);
  
 return 0;
}

int crcbuf(int crc, int len, char *buf)
{
 register int i;
 for (i=0; i<len; i++)
  crc = ((crc >> 8) & 0xff) ^ crctab[(crc ^ *buf++) & 0xff];
 
 return (crc);
}
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CompilerGuru
NXP Employee
NXP Employee
First, I have to say that I'm not the expert in CRC calculations, hopefully there are other people reading this here with more knowledge in this area.

The value I get is actually 0xABE7 (and not 0xABA7, is this a typo in your post?), and I get the same value from the linker at address 0xF800 and computed at runtime with the following code:


#include "checksum.h"
const char my_array[]@ 0xFD00 = {6,3,0xb, 0xb9,0,1};
void main(void) {
volatile int crc= _Checksum_CheckAreaCRC16(my_array, sizeof(my_array), 0xA001, 0xFFFF);
for(;:smileywink: {}
}

(and add checksum.c in lib\hc12c\src to your project)

Note that I did not use your table, how did you compute it given the 0xA001 polynom?

Daniel
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markiscarabas
Contributor I
Thanks a lot, and yes it was my typo. I will try to use the lib function too.:smileyhappy:
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