ardupilot/libraries/AP_Frsky_Telem/AP_Frsky_SPortParser.h

#pragma once

#include "AP_Frsky_SPort.h"

#if AP_FRSKY_SPORT_TELEM_ENABLED

#include <stdint.h>

// for SPort X protocol
#define FRAME_HEAD                  0x7E
#define FRAME_DLE                   0x7D
#define FRAME_XOR                   0x20
// for SPort D protocol
#define START_STOP_D                0x5E
#define BYTESTUFF_D                 0x5D
// for SPort packet parser
#define TELEMETRY_RX_BUFFER_SIZE    19U  // 9 bytes (full packet), worst case 18 bytes with byte-stuffing (+1)
#define SPORT_PACKET_SIZE           9U
#define STUFF_MASK                  0x20
#define SPORT_DATA_FRAME            0x10
#define SPORT_UPLINK_FRAME          0x30
#define SPORT_UPLINK_FRAME_RW       0x31
#define SPORT_DOWNLINK_FRAME        0x32

class AP_Frsky_SPortParser
{
public:

    // packet parser helpers
    bool process_byte(AP_Frsky_SPort::sport_packet_t &sport_packet, const uint8_t data);

private:
    enum class ParseState : uint8_t {
        IDLE,
        START,
        IN_FRAME,
        XOR,
    };

    struct {
        uint8_t rx_buffer_count;
        uint8_t rx_buffer[TELEMETRY_RX_BUFFER_SIZE];
        uint8_t last_packet[SPORT_PACKET_SIZE];
        ParseState state;
    } _parse_state;

    bool should_process_packet(const uint8_t *packet, bool discard_duplicates);
    bool get_packet(AP_Frsky_SPort::sport_packet_t &sport_packet, bool discard_duplicates);
};

#endif  // AP_FRSKY_SPORT_TELEM_ENABLED