kopia lustrzana https://github.com/SP8EBC/ParaTNC
51 wiersze
1.3 KiB
C
51 wiersze
1.3 KiB
C
/*
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* rtu_crc.h
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*
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* Created on: 18.09.2020
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* Author: mateusz
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*/
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#ifndef INCLUDE_MODBUS_RTU_RTU_CRC_H_
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#define INCLUDE_MODBUS_RTU_RTU_CRC_H_
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#include <stdint.h>
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inline uint16_t rtu_crc_stream(uint16_t previous_crc, uint8_t current_data) {
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int i;
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previous_crc ^= (uint16_t)current_data;
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for (i = 0; i < 8; ++i) {
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if (previous_crc & 1) {
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previous_crc = (previous_crc >> 1);
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previous_crc = (previous_crc) ^ 0xA001;
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}
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else
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previous_crc = (previous_crc >> 1);
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}
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return previous_crc;
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}
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inline uint16_t rtu_crc_buffer(uint8_t* buffer_ptr, uint8_t buffer_ln) {
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uint16_t crc = 0xFFFF;
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// https://ctlsys.com/support/how_to_compute_the_modbus_rtu_message_crc/
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for (int pos = 0; pos < buffer_ln; pos++) {
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crc ^= (uint16_t)buffer_ptr[pos]; // XOR byte into least sig. byte of crc
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for (int i = 8; i != 0; i--) { // Loop over each bit
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if ((crc & 0x0001) != 0) { // If the LSB is set
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crc >>= 1; // Shift right and XOR 0xA001
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crc ^= 0xA001;
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}
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else // Else LSB is not set
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crc >>= 1; // Just shift right
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}
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}
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// Note, this number has low and high bytes swapped, so use it accordingly (or swap bytes)
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return crc;
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}
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#endif /* INCLUDE_MODBUS_RTU_RTU_CRC_H_ */
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