CRC-16 Porblem - I'm not getting the correct result

[kotsam]

crcverify crc

Hey Guys ,

Another challange comming along ; i hope someone can help for this problem :

i found CRC16 in on of the websites : the code is below

//*****************CRC16**************************************

/* CRC16 Definitions */
static const unsigned char crc_table[256] = {
  0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
  0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
  0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
  0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
  0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
  0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
  0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
  0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
  0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
  0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
  0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
  0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
  0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
  0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
  0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
  0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
  0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
  0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
  0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
  0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
  0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
  0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
  0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
  0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
  0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
  0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
  0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
  0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
  0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
  0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
  0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
  0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
};

/* CRC calculation macros */
#define CRC_INIT 0xFFFF
#define CRC(crcval,newchar) crcval = (crcval >> 8) ^ \
	crc_table[(crcval ^ newchar) & 0x00ff]

unsigned short crcsum( const unsigned char *message, unsigned long length
      ,unsigned short crc)
{
  unsigned long i;

  for(i = 0; i < length; i++)
    {
      CRC(crc, message[i]);
    }
  return crc;
}


int
crcverify(const unsigned char* message, unsigned long length)
{
  /*
   * Returns true if the last two bytes in a message is the crc of the
   * preceding bytes.
   */

  unsigned short expected;

  expected = crcsum(message, length - 2, CRC_INIT);
  return (expected & 0xff) == message[length - 2] &&
    ((expected >> 8) & 0xff) == message[length - 1];
}

void
crcappend(unsigned char* message, unsigned long length)
{
  unsigned long crc;

  crc = crcsum(message, length, CRC_INIT);
  message[length] = (unsigned char)(crc & 0xff);
  message[length+1] = (unsigned char)((crc >> 8) & 0xff);
}

when i used this code i couldnt get the correct result

i have used the function as

CrcResult = crcsum (Buffer , 6 , CRC_INIT);

when i debug the code i found that i'm not getting the correct result ,
wen , i dont whats the problem for example :

my buffer : 3,3,0,5,0,2 the calculated CRC = D5,E8 but what i get from the function is 0x0078

i hope that someone can help me to solve this problem

 

[Encrypted]

fast crc16 0xa001

Hi,

There are many types of CRC. It seems like your trying to generate Modbus CRC-16 but the code your using generates CRC-16 for the Atmel Jtag Mk. II (CRC-CCITT).

See: https://www.lammertbies.nl/comm/info/crc-calculation.html?crc=030300050002&method=hex

If you change your lookup table then your code will generate the CRC you're looking for, see below:

static const unsigned short crc_table[256] = {
  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
};

Note: There's a mistake in your code; the table is an array of 16-bit values, so probably shorts and not chars.

 

[kotsam]

Re: CRC-16 Porblem

Hey ;

thanks alot for the help. u saying the i cant use the char at my table , when i'm using short it gives me error at the complie

Error - section '.idata_Modbus.o' can not fit the section. Section '.idata_Modbus.o' length=0x00000200

where i dont have this error at the when i'm using char ...

??? is there away to solve this thing aswell

thanks

 

[Encrypted]

Re: CRC-16 Porblem

OK, your constants are getting placed in RAM and you don't have enough for the large table. You can either tell your compiler not to put constants in RAM or use the modified version of your code below with a shorter table but not as fast.

/* CRC16 Definitions */
static const unsigned short crc_table[16] = {
  0x0000, 0xcc01, 0xd801, 0x1400, 0xf001, 0x3c00, 0x2800, 0xe401,
  0xa001, 0x6c00, 0x7800, 0xb401, 0x5000, 0x9c01, 0x8801, 0x4400
};

/* CRC calculation macros */ 
#define CRC_INIT 0xFFFF 
#define CRC(crcval,newchar) crcval = (crcval >> 8) ^ \
	crc_table[(crcval ^ newchar) & 0x00ff] 

unsigned short crcsum( const unsigned char *message, unsigned long length 
      ,unsigned short crc) 
{ 
  unsigned long i; 

  for(i = 0; i < length; i++) 
    { 
      //CRC(crc, message[i]);
	  crc ^= message[i];
	  crc = (crc >> 4) ^ crc_table[crc & 0x0f];
	  crc = (crc >> 4) ^ crc_table[crc & 0x0f];
    } 
  return crc; 
}