It might help with fast SPI comms (or UART) if you want to reduce the slow CRC calculation bottle neck with the TMC chips.
You can increase the 8-bit CRC calculation by quite a LOT if you wanted, I've written a couple of table driven CRC routines (a fast and a medium speed) ..
// define none or one of these
//#define CRC_FAST
//#define CRC_MEDIUM
// used if CRC_MEDIUM or CDC_FAST used
//#define BIT_REV_FAST
#define CRC8_POLY 0xE0 // 1110 0000 X^8 + X^2 + X^1 + X^0
#define CRC8_POLYR 0x07 // 0000 0111 X^8 + X^2 + X^1 + X^0
#if defined(CRC_FAST) || defined(CRC_MEDIUM)
#if defined(CRC_FAST)
constexpr uint8_t crc_table8[] =
{ // fast CRC table
0x00,0x91,0xe3,0x72,0x07,0x96,0xe4,0x75,0x0e,0x9f,0xed,0x7c,0x09,0x98,0xea,0x7b,
0x1c,0x8d,0xff,0x6e,0x1b,0x8a,0xf8,0x69,0x12,0x83,0xf1,0x60,0x15,0x84,0xf6,0x67,
0x38,0xa9,0xdb,0x4a,0x3f,0xae,0xdc,0x4d,0x36,0xa7,0xd5,0x44,0x31,0xa0,0xd2,0x43,
0x24,0xb5,0xc7,0x56,0x23,0xb2,0xc0,0x51,0x2a,0xbb,0xc9,0x58,0x2d,0xbc,0xce,0x5f,
0x70,0xe1,0x93,0x02,0x77,0xe6,0x94,0x05,0x7e,0xef,0x9d,0x0c,0x79,0xe8,0x9a,0x0b,
0x6c,0xfd,0x8f,0x1e,0x6b,0xfa,0x88,0x19,0x62,0xf3,0x81,0x10,0x65,0xf4,0x86,0x17,
0x48,0xd9,0xab,0x3a,0x4f,0xde,0xac,0x3d,0x46,0xd7,0xa5,0x34,0x41,0xd0,0xa2,0x33,
0x54,0xc5,0xb7,0x26,0x53,0xc2,0xb0,0x21,0x5a,0xcb,0xb9,0x28,0x5d,0xcc,0xbe,0x2f,
0xe0,0x71,0x03,0x92,0xe7,0x76,0x04,0x95,0xee,0x7f,0x0d,0x9c,0xe9,0x78,0x0a,0x9b,
0xfc,0x6d,0x1f,0x8e,0xfb,0x6a,0x18,0x89,0xf2,0x63,0x11,0x80,0xf5,0x64,0x16,0x87,
0xd8,0x49,0x3b,0xaa,0xdf,0x4e,0x3c,0xad,0xd6,0x47,0x35,0xa4,0xd1,0x40,0x32,0xa3,
0xc4,0x55,0x27,0xb6,0xc3,0x52,0x20,0xb1,0xca,0x5b,0x29,0xb8,0xcd,0x5c,0x2e,0xbf,
0x90,0x01,0x73,0xe2,0x97,0x06,0x74,0xe5,0x9e,0x0f,0x7d,0xec,0x99,0x08,0x7a,0xeb,
0x8c,0x1d,0x6f,0xfe,0x8b,0x1a,0x68,0xf9,0x82,0x13,0x61,0xf0,0x85,0x14,0x66,0xf7,
0xa8,0x39,0x4b,0xda,0xaf,0x3e,0x4c,0xdd,0xa6,0x37,0x45,0xd4,0xa1,0x30,0x42,0xd3,
0xb4,0x25,0x57,0xc6,0xb3,0x22,0x50,0xc1,0xba,0x2b,0x59,0xc8,0xbd,0x2c,0x5e,0xcf
};
#else // fast'ish CRC table
constexpr uint8_t crc_table8_1[] = {0x00,0x91,0xe3,0x72,0x07,0x96,0xe4,0x75,0x0e,0x9f,0xed,0x7c,0x09,0x98,0xea,0x7b};
constexpr uint8_t crc_table8_2[] = {0x00,0x1c,0x38,0x24,0x70,0x6c,0x48,0x54,0xe0,0xfc,0xd8,0xc4,0x90,0x8c,0xa8,0xb4};
#endif
#if defined(BIT_REV_FAST)
constexpr uint8_t bit_rev_table8[] =
{ // fast 8-bit reverse table
0x00,0x80,0x40,0xc0,0x20,0xa0,0x60,0xe0,0x10,0x90,0x50,0xd0,0x30,0xb0,0x70,0xf0,
0x08,0x88,0x48,0xc8,0x28,0xa8,0x68,0xe8,0x18,0x98,0x58,0xd8,0x38,0xb8,0x78,0xf8,
0x04,0x84,0x44,0xc4,0x24,0xa4,0x64,0xe4,0x14,0x94,0x54,0xd4,0x34,0xb4,0x74,0xf4,
0x0c,0x8c,0x4c,0xcc,0x2c,0xac,0x6c,0xec,0x1c,0x9c,0x5c,0xdc,0x3c,0xbc,0x7c,0xfc,
0x02,0x82,0x42,0xc2,0x22,0xa2,0x62,0xe2,0x12,0x92,0x52,0xd2,0x32,0xb2,0x72,0xf2,
0x0a,0x8a,0x4a,0xca,0x2a,0xaa,0x6a,0xea,0x1a,0x9a,0x5a,0xda,0x3a,0xba,0x7a,0xfa,
0x06,0x86,0x46,0xc6,0x26,0xa6,0x66,0xe6,0x16,0x96,0x56,0xd6,0x36,0xb6,0x76,0xf6,
0x0e,0x8e,0x4e,0xce,0x2e,0xae,0x6e,0xee,0x1e,0x9e,0x5e,0xde,0x3e,0xbe,0x7e,0xfe,
0x01,0x81,0x41,0xc1,0x21,0xa1,0x61,0xe1,0x11,0x91,0x51,0xd1,0x31,0xb1,0x71,0xf1,
0x09,0x89,0x49,0xc9,0x29,0xa9,0x69,0xe9,0x19,0x99,0x59,0xd9,0x39,0xb9,0x79,0xf9,
0x05,0x85,0x45,0xc5,0x25,0xa5,0x65,0xe5,0x15,0x95,0x55,0xd5,0x35,0xb5,0x75,0xf5,
0x0d,0x8d,0x4d,0xcd,0x2d,0xad,0x6d,0xed,0x1d,0x9d,0x5d,0xdd,0x3d,0xbd,0x7d,0xfd,
0x03,0x83,0x43,0xc3,0x23,0xa3,0x63,0xe3,0x13,0x93,0x53,0xd3,0x33,0xb3,0x73,0xf3,
0x0b,0x8b,0x4b,0xcb,0x2b,0xab,0x6b,0xeb,0x1b,0x9b,0x5b,0xdb,0x3b,0xbb,0x7b,0xfb,
0x07,0x87,0x47,0xc7,0x27,0xa7,0x67,0xe7,0x17,0x97,0x57,0xd7,0x37,0xb7,0x77,0xf7,
0x0f,0x8f,0x4f,0xcf,0x2f,0xaf,0x6f,0xef,0x1f,0x9f,0x5f,0xdf,0x3f,0xbf,0x7f,0xff
};
#else
constexpr uint8_t bit_rev_table4[] = {0x00,0x08,0x04,0x0c,0x02,0x0a,0x06,0x0e,0x01,0x09,0x05,0x0d,0x03,0x0b,0x07,0x0f};
uint8_t reverse_bits8(uint8_t x)
{ // fast'ish 8-bit reverse
return (bit_rev_table4[x & 0x0f] << 4) | bit_rev_table4[(x >> 4) & 0x0f];
}
#endif
#endif
/*
void makeCRC_tables()
{
#if defined(CRC_FAST)
for (uint16_t i = 0; i < 256; i++)
{
uint8_t crc = i;
for (uint8_t j = 8; j > 0; j--)
crc = (crc & 1) ? (crc >> 1) ^ CRC8_POLY : crc >> 1;
crc_table8[i] = crc;
}
#elif defined(CRC_MEDIUM)
for (uint8_t i = 0; i < 16; i++)
{
uint8_t crc = i;
for (uint8_t j = 8; j > 0; j--)
crc = (crc & 1) ? (crc >> 1) ^ CRC8_POLY : crc >> 1;
crc_table8_1[i] = crc;
}
for (uint16_t i = 0; i < 16; i++)
{
uint8_t crc = i << 4;
for (uint8_t j = 8; j > 0; j--)
crc = (crc & 1) ? (crc >> 1) ^ CRC8_POLY : crc >> 1;
crc_table8_2[i] = crc;
}
#endif
}
*/
uint8_t TMC2208Stepper::calcCRC(uint8_t datagram[], uint8_t len) {
uint8_t crc = 0;
uint8_t *data = datagram;
#if defined(CRC_FAST)
for (uint8_t i = len; i > 0; i--)
{
crc ^= *data++;
crc = crc_table8[crc];
}
#elif defined(CRC_MEDIUM)
for (uint8_t i = len; i > 0; i--)
{
crc ^= *data++;
crc = crc_table8_1[crc & 0x0f] ^ crc_table8_2[(crc >> 4) & 0x0f];
}
#else
for (uint8_t i = len; i > 0; i--)
{
uint8_t c = *data++;
for (uint8_t j = 8; j > 0; j--)
{
crc = ((crc >> 7) ^ (c & 1)) ? (crc << 1) ^ CRC8_POLYR : crc << 1;
c >>= 1;
}
}
#endif
#if defined(CRC_FAST) || defined(CRC_MEDIUM)
#if defined(BIT_REV_FAST)
crc = bit_rev_table8[crc];
#else
crc = reverse_bits8(crc);
#endif
#endif
return crc;
}
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