mtk.h

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/**
 * @file mtk.h
 *
 * @author Thomas Gubler <thomasgubler@student.ethz.ch>
 * @author Julian Oes <julian@oes.ch>
 */

#pragma once

#include "gps_helper.h"

#define MTK_SYNC1_V16 0xd0
#define MTK_SYNC1_V19 0xd1
#define MTK_SYNC2 0xdd

#define MTK_OUTPUT_5HZ		"$PMTK220,200*2C\r\n"
#define MTK_SET_BINARY		"$PGCMD,16,0,0,0,0,0*6A\r\n"
#define MTK_SBAS_ON	       	"$PMTK313,1*2E\r\n"
#define MTK_WAAS_ON		"$PMTK301,2*2E\r\n"
#define MTK_NAVTHRES_OFF 	"$PMTK397,0*23\r\n"

#define MTK_TIMEOUT_5HZ 400
#define MTK_BAUDRATE 38400

typedef enum {
	MTK_DECODE_UNINIT = 0,
	MTK_DECODE_GOT_CK_A = 1,
	MTK_DECODE_GOT_CK_B = 2
} mtk_decode_state_t;

/** the structures of the binary packets */
#pragma pack(push, 1)

typedef struct {
	uint8_t payload; ///< Number of payload bytes
	int32_t latitude;  ///< Latitude in degrees * 10^7
	int32_t longitude; ///< Longitude in degrees * 10^7
	uint32_t msl_altitude;  ///< MSL altitude in meters * 10^2
	uint32_t ground_speed; ///< velocity in m/s
	int32_t heading; ///< heading in degrees * 10^2
	uint8_t satellites; ///< number of satellites used
	uint8_t fix_type;  ///< fix type: XXX correct for that
	uint32_t date;
	uint32_t utc_time;
	uint16_t hdop; ///< horizontal dilution of position (without unit)
	uint8_t ck_a;
	uint8_t ck_b;
} gps_mtk_packet_t;

#pragma pack(pop)

#define MTK_RECV_BUFFER_SIZE 40

class GPSDriverMTK : public GPSHelper
{
public:
	GPSDriverMTK(GPSCallbackPtr callback, void *callback_user, sensor_gps_s *gps_position);
	virtual ~GPSDriverMTK() = default;

	int receive(unsigned timeout) override;
	int configure(unsigned &baudrate, const GPSConfig &config) override;

private:
	/**
	 * Parse the binary MTK packet
	 */
	int parseChar(uint8_t b, gps_mtk_packet_t &packet);

	/**
	 * Handle the package once it has arrived
	 */
	void handleMessage(gps_mtk_packet_t &packet);

	/**
	 * Reset the parse state machine for a fresh start
	 */
	void decodeInit();

	/**
	 * While parsing add every byte (except the sync bytes) to the checksum
	 */
	void addByteToChecksum(uint8_t);

	sensor_gps_s *_gps_position {nullptr};
	mtk_decode_state_t _decode_state{MTK_DECODE_UNINIT};
	uint8_t _mtk_revision{0};
	unsigned _rx_count{};
	uint8_t _rx_ck_a{};
	uint8_t _rx_ck_b{};
};