/* The check_crc16 function shall return the message length if the CRC is
valid. Otherwise it shall return -1 and set errno to EMBADCRC. */
int _modbus_rtu_check_integrity(modbus_t *ctx, uint8_t *msg,
const int msg_length)
{
uint16_t crc_calculated;
uint16_t crc_received;
crc_calculated = crc16(msg, msg_length - 2);
crc_received = (msg[msg_length - 2] << 8) | msg[msg_length - 1];
ctx->last_crc_expected = crc_calculated;
ctx->last_crc_received = crc_received;
/* Check CRC of msg */
if (crc_calculated == crc_received) {
return msg_length;
} else {
if (ctx->debug) {
fprintf(stderr, "ERROR CRC received %0X != CRC calculated %0X\n",
crc_received, crc_calculated);
}
if (ctx->error_recovery) {
_modbus_rtu_flush(ctx);
}
errno = EMBBADCRC;
return -1;
}
}
/* The check_crc16 function shall return 0 is the message is ignored and the
message length if the CRC is valid. Otherwise it shall return -1 and set
errno to EMBADCRC. */
static int _modbus_rtu_check_integrity(modbus_t *ctx, uint8_t *msg,
const int msg_length)
{
uint16_t crc_calculated;
uint16_t crc_received;
int slave = msg[0];
/* Filter on the Modbus unit identifier (slave) in RTU mode to avoid useless
* CRC computing. */
if (slave != ctx->slave && slave != MODBUS_BROADCAST_ADDRESS) {
if (ctx->debug) {
printf("Request for slave %d ignored (not %d)\n", slave, ctx->slave);
}
/* Following call to check_confirmation handles this error */
return 0;
}
crc_calculated = crc16(msg, msg_length - 2);
crc_received = (msg[msg_length - 2] << 8) | msg[msg_length - 1];
ctx->last_crc_expected = crc_calculated;
ctx->last_crc_received = crc_received;
/* Check CRC of msg */
if (crc_calculated == crc_received) {
return msg_length;
} else {
if (ctx->debug) {
fprintf(stderr, "ERROR CRC received %0X != CRC calculated %0X\n",
crc_received, crc_calculated);
}
if (ctx->error_recovery & MODBUS_ERROR_RECOVERY_PROTOCOL) {
_modbus_rtu_flush(ctx);
}
errno = EMBBADCRC;
return -1;
}
}
/* The check_crc16 function shall return 0 is the message is ignored and the
message length if the CRC is valid. Otherwise it shall return -1 and set
errno to EMBADCRC. */
int _modbus_rtu_check_integrity(modbus_t *ctx, uint8_t *msg,
const int msg_length)
{
uint16_t crc_calculated;
uint16_t crc_received;
int slave = msg[0];
/* Filter on the Modbus unit identifier (slave) in RTU mode */
if (slave != ctx->slave && slave != MODBUS_BROADCAST_ADDRESS) {
/* Ignores the request (not for me) */
if (ctx->debug) {
printf("Request for slave %d ignored (not %d)\n", slave, ctx->slave);
}
return 0;
}
crc_calculated = crc16(msg, msg_length - 2);
crc_received = (msg[msg_length - 2] << 8) | msg[msg_length - 1];
/* Check CRC of msg */
if (crc_calculated == crc_received) {
return msg_length;
} else {
if (ctx->debug) {
fprintf(stderr, "ERROR CRC received %0X != CRC calculated %0X\n",
crc_received, crc_calculated);
}
if (ctx->error_recovery & MODBUS_ERROR_RECOVERY_PROTOCOL) {
_modbus_rtu_flush(ctx);
}
errno = EMBBADCRC;
return -1;
}
}
