Seeed / mbedPebbleSerial

a serial library to communicate with pebble time's smart strap interface

Dependents:   xadow_smartstrap_for_pebble

crc.c@0:e4dad9e53f06, 2015-11-04 (annotated)

Committer:
KillingJacky
Date:
Wed Nov 04 09:58:41 2015 +0000
Revision:
0:e4dad9e53f06
initial commit;

Who changed what in which revision?

UserRevisionLine numberNew contents of line
KillingJacky 0:e4dad9e53f06 1 #include "crc.h"
KillingJacky 0:e4dad9e53f06 2
KillingJacky 0:e4dad9e53f06 3 void crc8_calculate_byte_streaming(const uint8_t data, uint8_t *crc) {
KillingJacky 0:e4dad9e53f06 4 // Optimal polynomial chosen based on
KillingJacky 0:e4dad9e53f06 5 // http://users.ece.cmu.edu/~koopman/roses/dsn04/koopman04_crc_poly_embedded.pdf
KillingJacky 0:e4dad9e53f06 6 // Note that this is different than the standard CRC-8 polynomial, because the
KillingJacky 0:e4dad9e53f06 7 // standard CRC-8 polynomial is not particularly good.
KillingJacky 0:e4dad9e53f06 8
KillingJacky 0:e4dad9e53f06 9 // nibble lookup table for (x^8 + x^5 + x^3 + x^2 + x + 1)
KillingJacky 0:e4dad9e53f06 10 static const uint8_t lookup_table[] =
KillingJacky 0:e4dad9e53f06 11 { 0, 47, 94, 113, 188, 147, 226, 205, 87, 120, 9, 38, 235, 196,
KillingJacky 0:e4dad9e53f06 12 181, 154 };
KillingJacky 0:e4dad9e53f06 13
KillingJacky 0:e4dad9e53f06 14 int i;
KillingJacky 0:e4dad9e53f06 15 for (i = 2; i > 0; i--) {
KillingJacky 0:e4dad9e53f06 16 uint8_t nibble = data;
KillingJacky 0:e4dad9e53f06 17 if (i % 2 == 0) {
KillingJacky 0:e4dad9e53f06 18 nibble >>= 4;
KillingJacky 0:e4dad9e53f06 19 }
KillingJacky 0:e4dad9e53f06 20 int index = nibble ^ (*crc >> 4);
KillingJacky 0:e4dad9e53f06 21 *crc = lookup_table[index & 0xf] ^ (*crc << 4);
KillingJacky 0:e4dad9e53f06 22 }
KillingJacky 0:e4dad9e53f06 23 }