st24.h

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/**
 * @file st24.h
 *
 * RC protocol definition for Yuneec ST24 transmitter
 *
 * @author Lorenz Meier <lm@inf.ethz.ch>
 */

#pragma once

#include <stdint.h>

__BEGIN_DECLS

#define ST24_DATA_LEN_MAX   64
#define ST24_STX1       0x55
#define ST24_STX2       0x55

enum ST24_PACKET_TYPE {
    ST24_PACKET_TYPE_CHANNELDATA12 = 0,
    ST24_PACKET_TYPE_CHANNELDATA24,
    ST24_PACKET_TYPE_TRANSMITTERGPSDATA
};

enum ST24_DECODE_STATE {
    ST24_DECODE_STATE_UNSYNCED = 0,
    ST24_DECODE_STATE_GOT_STX1,
    ST24_DECODE_STATE_GOT_STX2,
    ST24_DECODE_STATE_GOT_LEN,
    ST24_DECODE_STATE_GOT_TYPE,
    ST24_DECODE_STATE_GOT_DATA
};

#pragma pack(push, 1)
typedef struct {
    uint8_t header1;            ///< 0x55 for a valid packet
    uint8_t header2;            ///< 0x55 for a valid packet
    uint8_t length;             ///< length includes type, data, and crc = sizeof(type)+sizeof(data[payload_len])+sizeof(crc8)
    uint8_t type;               ///< from enum ST24_PACKET_TYPE
    uint8_t st24_data[ST24_DATA_LEN_MAX];
    uint8_t crc8;               ///< crc8 checksum, calculated by st24_common_crc8 and including fields length, type and st24_data
} ReceiverFcPacket;

/**
 * RC Channel data (12 channels).
 *
 * This is incoming from the ST24
 */
typedef struct {
    uint16_t t;         ///< packet counter or clock
    uint8_t rssi;           ///< signal strength
    uint8_t lost_count;     ///< Number of UART packets sent since reception of last RF frame (100 frame means RC timeout of 1s)
    uint8_t channel[18];        ///< channel data, 12 channels (12 bit numbers)
} ChannelData12;

/**
 * RC Channel data (12 channels).
 *
 */
typedef struct {
    uint16_t t;         ///< packet counter or clock
    uint8_t rssi;           ///< signal strength
    uint8_t lost_count;     ///< Number of UART packets sent since reception of last RF frame (100 frame means RC timeout of 1s)
    uint8_t channel[36];        ///< channel data, 24 channels (12 bit numbers)
} ChannelData24;

/**
 * Telemetry packet
 *
 * This is outgoing to the ST24
 *
 * imuStatus:
 * 8 bit total
 * bits 0-2 for status
 * - value 0 is FAILED
 * - value 1 is INITIALIZING
 * - value 2 is RUNNING
 * - values 3 through 7 are reserved
 * bits 3-7 are status for sensors (0 or 1)
 * - mpu6050
 * - accelerometer
 * - primary gyro x
 * - primary gyro y
 * - primary gyro z
 *
 * pressCompassStatus
 * 8 bit total
 * bits 0-3 for compass status
 * - value 0 is FAILED
 * - value 1 is INITIALIZING
 * - value 2 is RUNNING
 * - value 3 - 15 are reserved
 * bits 4-7 for pressure status
 * - value 0 is FAILED
 * - value 1 is INITIALIZING
 * - value 2 is RUNNING
 * - value 3 - 15 are reserved
 *
 */
typedef struct {
    uint16_t t;         ///< packet counter or clock
    int32_t lat;            ///< lattitude (degrees)    +/- 90 deg
    int32_t lon;            ///< longitude (degrees)    +/- 180 deg
    int32_t alt;            ///< 0.01m resolution, altitude (meters)
    int16_t vx, vy, vz;         ///< velocity 0.01m res, +/-320.00 North-East- Down
    uint8_t nsat;           ///<number of satellites
    uint8_t voltage;        ///< 25.4V  voltage = 5 + 255*0.1 = 30.5V, min=5V
    uint8_t current;        ///< 0.5A resolution
    int16_t roll, pitch, yaw;   ///< 0.01 degree resolution
    uint8_t motorStatus;        ///< 1 bit per motor for status 1=good, 0= fail
    uint8_t imuStatus;      ///< inertial measurement unit status
    uint8_t pressCompassStatus; ///< baro / compass status
} TelemetryData;

#pragma pack(pop)

/**
 * CRC8 implementation for ST24 protocol
 *
 * @param prt Pointer to the data to CRC
 * @param len number of bytes to accumulate in the checksum
 * @return the checksum of these bytes over len
 */
uint8_t st24_common_crc8(uint8_t *ptr, uint8_t len);

/**
 * Decoder for ST24 protocol
 *
 * @param byte current char to read
 * @param rssi pointer to a byte where the RSSI value is written back to
 * @param lost_count pointer to a byte where the receive count of packets since last wireless frame is written back to ( > 0 if RC is lost)
 * @param channels pointer to a datastructure of size max_chan_count where channel values (12 bit) are written back to
 * @param max_chan_count maximum channels to decode - if more channels are decoded, the last n are skipped and success (0) is returned
 * @return 0 for success (a decoded packet), 1 for no packet yet (accumulating), 2 for unknown packet, 3 for out of sync, 4 for checksum error
 */
__EXPORT int st24_decode(uint8_t byte, uint8_t *rssi, uint8_t *lost_count, uint16_t *channel_count,
             uint16_t *channels, uint16_t max_chan_count);

__END_DECLS