Question: How to calculate a series data byte for CRC-16 value?


Can anyone advise me how to perform the CRC-16 for series byte data correctly. I’d like to calculated 5 bytes (ON={0xA5,0x05,0x4C,0x4C,0x42}) for CRC value, but system shows the error message. Your reply will be highly appreciated.

" CRC_Test_checkTable:79: error: expected primary-expression before ‘]’ token"



#include <stdio.h>
#include <stdint.h>

static const uint16_t crctable[256] =
0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
0x0919, 0x1890, 0x2A0B, 0x3B82, 0x4F3D, 0x5EB4, 0x6C2F, 0x7DA6,
0x8551, 0x94D8, 0xA643, 0xB7CA, 0xC375, 0xD2FC, 0xE067, 0xF1EE,
0x1232, 0x03BB, 0x3120, 0x20A9, 0x5416, 0x459F, 0x7704, 0x668D,
0x9E7A, 0x8FF3, 0xBD68, 0xACE1, 0xD85E, 0xC9D7, 0xFB4C, 0xEAC5,
0x1B2B, 0x0AA2, 0x3839, 0x29B0, 0x5D0F, 0x4C86, 0x7E1D, 0x6F94,
0x9763, 0x86EA, 0xB471, 0xA5F8, 0xD147, 0xC0CE, 0xF255, 0xE3DC,
0x2464, 0x35ED, 0x0776, 0x16FF, 0x6240, 0x73C9, 0x4152, 0x50DB,
0xA82C, 0xB9A5, 0x8B3E, 0x9AB7, 0xEE08, 0xFF81, 0xCD1A, 0xDC93,
0x2D7D, 0x3CF4, 0x0E6F, 0x1FE6, 0x6B59, 0x7AD0, 0x484B, 0x59C2,
0xA135, 0xB0BC, 0x8227, 0x93AE, 0xE711, 0xF698, 0xC403, 0xD58A,
0x3656, 0x27DF, 0x1544, 0x04CD, 0x7072, 0x61FB, 0x5360, 0x42E9,
0xBA1E, 0xAB97, 0x990C, 0x8885, 0xFC3A, 0xEDB3, 0xDF28, 0xCEA1,
0x3F4F, 0x2EC6, 0x1C5D, 0x0DD4, 0x796B, 0x68E2, 0x5A79, 0x4BF0,
0xB307, 0xA28E, 0x9015, 0x819C, 0xF523, 0xE4AA, 0xD631, 0xC7B8,
0x48C8, 0x5941, 0x6BDA, 0x7A53, 0x0EEC, 0x1F65, 0x2DFE, 0x3C77,
0xC480, 0xD509, 0xE792, 0xF61B, 0x82A4, 0x932D, 0xA1B6, 0xB03F,
0x41D1, 0x5058, 0x62C3, 0x734A, 0x07F5, 0x167C, 0x24E7, 0x356E,
0xCD99, 0xDC10, 0xEE8B, 0xFF02, 0x8BBD, 0x9A34, 0xA8AF, 0xB926,
0x5AFA, 0x4B73, 0x79E8, 0x6861, 0x1CDE, 0x0D57, 0x3FCC, 0x2E45,
0xD6B2, 0xC73B, 0xF5A0, 0xE429, 0x9096, 0x811F, 0xB384, 0xA20D,
0x53E3, 0x426A, 0x70F1, 0x6178, 0x15C7, 0x044E, 0x36D5, 0x275C,
0xDFAB, 0xCE22, 0xFCB9, 0xED30, 0x998F, 0x8806, 0xBA9D, 0xAB14,
0x6CAC, 0x7D25, 0x4FBE, 0x5E37, 0x2A88, 0x3B01, 0x099A, 0x1813,
0xE0E4, 0xF16D, 0xC3F6, 0xD27F, 0xA6C0, 0xB749, 0x85D2, 0x945B,
0x65B5, 0x743C, 0x46A7, 0x572E, 0x2391, 0x3218, 0x0083, 0x110A,
0xE9FD, 0xF874, 0xCAEF, 0xDB66, 0xAFD9, 0xBE50, 0x8CCB, 0x9D42,
0x7E9E, 0x6F17, 0x5D8C, 0x4C05, 0x38BA, 0x2933, 0x1BA8, 0x0A21,
0xF2D6, 0xE35F, 0xD1C4, 0xC04D, 0xB4F2, 0xA57B, 0x97E0, 0x8669,
0x7787, 0x660E, 0x5495, 0x451C, 0x31A3, 0x202A, 0x12B1, 0x0338,
0xFBCF, 0xEA46, 0xD8DD, 0xC954, 0xBDEB, 0xAC62, 0x9EF9, 0x8F70
uint16_t crc_check;
byte ON={0xA5,0x05,0x4C,0x4C,0x42};
char *buffer;

void setup() {
//Initialize serial and wait for port to open:

uint16_t // Returns Calculated CRC value
uint16_t crc, // Seed for CRC calculation
const void *c_ptr, // Pointer to byte array to perform CRC on
size_t len) // Number of bytes to CRC
// const uint8_t *c = c_ptr;
const uint8_t c = (const uint8_t)c_ptr;

while (len–)
crc = (crc << 8) ^ crctable[((crc >> 8) ^ *c++)];
Serial.print("In loop CRC: ");
return crc;

void loop()
crc_check=CalculateCRC16(0x0000, buffer , 5);
Serial.print("CRC: ");

Hello and welcome :)

You can just do:

crc_check=CalculateCRC16(0x0000, ON , 5);


The error you report is due to a syntax error in the first line of your loop function. buffer=ON[]; You cant declare a variable without specifying its type.


Since you have already declared buffer as a global variable you shouldn't need it here anyhow. So just delete buffer=ON[]; from your loop and it will remove the syntax error

Great! It's working now.

After remove the line


and modified

crc_check=CalculateCRC16(0x0000, ON , 5);

Thanks for guix & KenF kindly support.

You can also use sizeof so you don’t need to care about changing the length manually if you modify your array.

crc_check=CalculateCRC16( 0x0000, ON , sizeof(ON) );

Additionally, I see you don’t really understand pointers etc and you made it more complicated than it could be:

uint16_t CalculateCRC16( uint16_t crc, const uint8_t *c_ptr, size_t len )
    while (len--)
        crc = (crc << 8) ^ crctable[((crc >> 8) ^ *c_ptr++)];
        Serial.print("In loop CRC: ");
    return crc;

And your big array is constant, so you could put in inside progmem, it’s as simple as doing:

const uint16_t PROGMEM crctable[] =

it’s as simple as doing:

const uint16_t PROGMEM crctable[] =

I don’t think it’s as simple as that! Yes you can put the array in program memory but I think you need

a) To include
#include <avr/pgmspace.h>
b) To define the array as
static const PROGMEM prog_uint16_t crctable[256] =
c) To change the crc calculation line to

   crc = (crc << 8) ^ pgm_read_word_near(crctable + ((crc >> 8) ^ *c++));


I should have said that the page I linked to, is outdated. Those prog_* typedefs are deprecated. Static doesn't really need to be used because the array is global, and the size is optional :P

So, a) and b) are unneeded changes

For c), I just didn't want to spoon feed him :P

Also see this.