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Corrected the CRC7 code with the right sequence of instructions.

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This commit is contained in:
Jacob Pease 2024-07-22 01:19:10 -05:00
parent c7d869bc96
commit e91d2c8b14
1 changed files with 6 additions and 3 deletions
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9
fpga/zsbl/sd.c
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@ -1,12 +1,15 @@
#include "sd.h" #include "sd.h"
#include "spi.h" #include "spi.h"
// Parallel byte update CRC7-CCITT algorithm.
// The result is the CRC7 result, left shifted over by 1
// which is perfect, since we append a 1 at the end anyway
uint8_t crc7(uint8_t prev, uint8_t in) { uint8_t crc7(uint8_t prev, uint8_t in) {
// CRC polynomial 0x89 // CRC polynomial 0x89
uint8_t remainder = prev & in; uint8_t remainder = prev ^ in;
remainder ^= (remainder >> 4) ^ (remainder >> 7); remainder ^= (remainder >> 4) ^ (remainder >> 7);
remainder ^= remainder << 4; remainder = (remainder << 1) ^ (remainder << 4);
return remainder & 0x7f; return remainder & 0xff;
} }
uint16_t crc16(uint16_t crc, uint8_t data) { uint16_t crc16(uint16_t crc, uint8_t data) {