I'm having problems with my CRC calculations on PIC24FV32KA301.
I have tried two different CRC-16 computation methods using 1, 2, and
3 bytes of data and only 1 of them is resulting in the correct answer.

Does anyone know wtf I'm doing wrong? I'd appreciate any help.



Here is the relevant code,

//Code borrowed from:
http://ww1.microchip.com/downloads/en/DeviceDoc/CE312%20CRC.zip

#define uint unsigned int
#define uchar unsigned char

unsigned int crc_calc(uchar * data, uint datalen, uint poly, uint
polylen, uint datawidth, uint prevcrc) {
    CRCCON1bits.CRCEN =3D 1;

    CRCXOR =3D poly;
    CRCCON2bits.PLEN =3D polylen - 1;     //Poly length =3D PLEN + 1
    CRCCON2bits.DWIDTH =3D datawidth - 1; //Data word width =3D DWIDTH + 1
    CRCCON1bits.LENDIAN =3D 0;            //MSb big endian
    CRCCON1bits.CRCISEL =3D 0;

    CRCWDAT =3D prevcrc;

    CRCCON1bits.CRCGO =3D 1;              //Start CRC serial shifter

    do {
        while(CRCCON1bits.CRCMPT =3D=3D 0);
        while((CRCCON1bits.CRCFUL =3D=3D 0) && (datalen > 0)) {
            CRCDAT =3D *data;
            data++;
            datalen--;
        }
    } while (datalen > 0);

    while(CRCCON1bits.CRCFUL =3D=3D 1);     //Wait if FIFO is full

    CRCDAT =3D 0x0000;
    while(CRCCON1bits.CRCMPT =3D=3D 0);     //Wait FIFO empty
    CRCCON1bits.CRCGO =3D 0;              //CRC serial shifter turned off
    return (CRCWDAT);

}

void main(void) {
uchar data[10] =3D "abcdefg";

//Results compared to:
//http://www.lammertbies.nl/comm/info/crc-calculation.html
//                                                 Result
uint crc1 =3D crc_calc(data, 1, 0x1021, 16, 8, 0); //0x7C87 =3D RIGHT
uint crc2 =3D crc_calc(data, 1, 0x8005, 16, 8, 0); //0x8145 =3D WRONG ->
should be 0xA87E
uint crc3 =3D crc_calc(data, 2, 0x1021, 16, 8, 0); //0xE0BF =3D WRONG ->
should be 0X74FF
uint crc4 =3D crc_calc(data, 2, 0x8005, 16, 8, 0); //0x06D8 =3D WRONG ->
should be 0xC9A9
uint crc5 =3D crc_calc(data, 3, 0x1021, 16, 8, 0); //0x1A43 =3D WRONG ->
should be 0x9DD6
uint crc6 =3D crc_calc(data, 3, 0x8005, 16, 8, 0); //0x179A =3D WRONG ->
should be 0x9738
}
--=20
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