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Fix inconsistency between mbed crc and psoc6 crc implementations.

pull/12324/head
Dustin Crossman 2020-01-23 20:46:37 +00:00
parent 7101e92d12
commit b204dfd943
1 changed files with 17 additions and 1 deletions
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18
targets/TARGET_Cypress/TARGET_PSOC6/cy_crc_api.c
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@ -31,6 +31,14 @@ static cyhal_crc_t cy_crc;
static crc_algorithm_t cy_crc_cfg;
static bool cy_crc_initialized = false;
// Reverses width least significant bits of 32 bit input. Any bits more
// significant than width are dropped.
static uint32_t reverse(uint8_t width, uint32_t in)
{
MBED_ASSERT(width <= 32);
return __RBIT(in) >> (32 - width);
}
void hal_crc_compute_partial_start(const crc_mbed_config_t *config)
{
if (!cy_crc_initialized) {
@ -46,9 +54,17 @@ void hal_crc_compute_partial_start(const crc_mbed_config_t *config)
cy_crc_cfg.polynomial = config->polynomial;
cy_crc_cfg.lfsrInitState = config->initial_xor;
cy_crc_cfg.dataXor = 0;
cy_crc_cfg.remXor = config->final_xor;
cy_crc_cfg.dataReverse = config->reflect_in ? 1 : 0;
cy_crc_cfg.remReverse = config->reflect_out ? 1 : 0;
// There is an incongruity between what MBeds CRC spec expects and what
// PSoC6 hardware actually performs when it comes to the final XOR and
// remainder reversal: MBed expects the final remainder to be reversed then
// XORed with remXor while PSoC6s CRC, however, performs the final XOR with
// remXor then reverses the resulting value. Since Rev(A) XOR B == Rev( A
// XOR Rev(B) ), a simple fix is to reverse remXor if reflect_out is true.
cy_crc_cfg.remXor = config->reflect_out ? reverse(config->width, config->final_xor) : config->final_xor;
if (CY_RSLT_SUCCESS != cyhal_crc_start(&cy_crc, &cy_crc_cfg)) {
MBED_ERROR(MBED_MAKE_ERROR(MBED_MODULE_DRIVER, MBED_ERROR_CODE_FAILED_OPERATION), "cyhal_crc_start");
}