Merge pull request #294 from sjwilks/hott_v2

Add GPS Support to the HoTT Telemetry driver

3 files changed, 306 insertions, 114 deletions

diff --git a/src/drivers/hott_telemetry/hott_telemetry_main.c b/src/drivers/hott_telemetry/hott_telemetry_main.c
index a13a6ef58..4318244f8 100644
--- a/src/drivers/hott_telemetry/hott_telemetry_main.c
+++ b/src/drivers/hott_telemetry/hott_telemetry_main.c
@@ -53,6 +53,7 @@
 #include <termios.h>
 #include <sys/ioctl.h>
 #include <unistd.h>
+#include <systemlib/err.h>
 #include <systemlib/systemlib.h>
 
 #include "messages.h"
@@ -60,56 +61,44 @@
 static int thread_should_exit = false;		/**< Deamon exit flag */
 static int thread_running = false;		/**< Deamon status flag */
 static int deamon_task;				/**< Handle of deamon task / thread */
-static char *daemon_name = "hott_telemetry";
-static char *commandline_usage = "usage: hott_telemetry start|status|stop [-d <device>]";
+static const char daemon_name[] = "hott_telemetry";
+static const char commandline_usage[] = "usage: hott_telemetry start|status|stop [-d <device>]";
 
-
-/* A little console messaging experiment - console helper macro */
-#define FATAL_MSG(_msg)		fprintf(stderr, "[%s] %s\n", daemon_name, _msg); exit(1);
-#define ERROR_MSG(_msg)		fprintf(stderr, "[%s] %s\n", daemon_name, _msg);
-#define INFO_MSG(_msg)		printf("[%s] %s\n", daemon_name, _msg);
 /**
  * Deamon management function.
  */
 __EXPORT int hott_telemetry_main(int argc, char *argv[]);
 
 /**
- * Mainloop of deamon.
+ * Mainloop of daemon.
  */
 int hott_telemetry_thread_main(int argc, char *argv[]);
 
-static int read_data(int uart, int *id);
-static int send_data(int uart, uint8_t *buffer, int size);
+static int recv_req_id(int uart, uint8_t *id);
+static int send_data(int uart, uint8_t *buffer, size_t size);
 
-static int open_uart(const char *device, struct termios *uart_config_original)
+static int
+open_uart(const char *device, struct termios *uart_config_original)
 {
 	/* baud rate */
-	int speed = B19200;
-	int uart;
+	static const speed_t speed = B19200;
 
 	/* open uart */
-	uart = open(device, O_RDWR | O_NOCTTY);
+	const int uart = open(device, O_RDWR | O_NOCTTY);
 
 	if (uart < 0) {
-		char msg[80];
-		sprintf(msg, "Error opening port: %s\n", device);
-		FATAL_MSG(msg);
+		err(1, "Error opening port: %s", device);
 	}
-
-	/* Try to set baud rate */
-	struct termios uart_config;
+	
+	/* Back up the original uart configuration to restore it after exit */	
 	int termios_state;
-
-	/* Back up the original uart configuration to restore it after exit */
-	char msg[80];
-
 	if ((termios_state = tcgetattr(uart, uart_config_original)) < 0) {
-		sprintf(msg, "Error getting baudrate / termios config for %s: %d\n", device, termios_state);
 		close(uart);
-		FATAL_MSG(msg);
+		err(1, "Error getting baudrate / termios config for %s: %d", device, termios_state);
 	}
 
 	/* Fill the struct for the new configuration */
+	struct termios uart_config;
 	tcgetattr(uart, &uart_config);
 
 	/* Clear ONLCR flag (which appends a CR for every LF) */
@@ -117,16 +106,14 @@ static int open_uart(const char *device, struct termios *uart_config_original)
 
 	/* Set baud rate */
 	if (cfsetispeed(&uart_config, speed) < 0 || cfsetospeed(&uart_config, speed) < 0) {
-		sprintf(msg, "Error setting baudrate / termios config for %s: %d (cfsetispeed, cfsetospeed)\n",
-			device, termios_state);
 		close(uart);
-		FATAL_MSG(msg);
+		err(1, "Error setting baudrate / termios config for %s: %d (cfsetispeed, cfsetospeed)",
+			 device, termios_state);
 	}
 
 	if ((termios_state = tcsetattr(uart, TCSANOW, &uart_config)) < 0) {
-		sprintf(msg, "Error setting baudrate / termios config for %s (tcsetattr)\n", device);
 		close(uart);
-		FATAL_MSG(msg);
+		err(1, "Error setting baudrate / termios config for %s (tcsetattr)", device);
 	}
 
 	/* Activate single wire mode */
@@ -135,39 +122,42 @@ static int open_uart(const char *device, struct termios *uart_config_original)
 	return uart;
 }
 
-int read_data(int uart, int *id)
+int
+recv_req_id(int uart, uint8_t *id)
 {
-	const int timeout = 1000;
+	static const int timeout_ms = 1000;  // TODO make it a define
 	struct pollfd fds[] = { { .fd = uart, .events = POLLIN } };
 
-	char mode;
+	uint8_t mode;
 
-	if (poll(fds, 1, timeout) > 0) {
+	if (poll(fds, 1, timeout_ms) > 0) {
 		/* Get the mode: binary or text  */
-		read(uart, &mode, 1);
+		read(uart, &mode, sizeof(mode));
 		/* Read the device ID being polled */
-		read(uart, id, 1);
+		read(uart, id, sizeof(*id));
 
 		/* if we have a binary mode request */
 		if (mode != BINARY_MODE_REQUEST_ID) {
+			warnx("Non binary request ID detected: %d", mode);
 			return ERROR;
 		}
 
 	} else {
-		ERROR_MSG("UART timeout on TX/RX port");
+		warnx("UART timeout on TX/RX port");
 		return ERROR;
 	}
 
 	return OK;
 }
 
-int send_data(int uart, uint8_t *buffer, int size)
+int
+send_data(int uart, uint8_t *buffer, size_t size)
 {
 	usleep(POST_READ_DELAY_IN_USECS);
 
 	uint16_t checksum = 0;
 
-	for (int i = 0; i < size; i++) {
+	for (size_t i = 0; i < size; i++) {
 		if (i == size - 1) {
 			/* Set the checksum: the first uint8_t is taken as the checksum. */
 			buffer[i] = checksum & 0xff;
@@ -176,7 +166,7 @@ int send_data(int uart, uint8_t *buffer, int size)
 			checksum += buffer[i];
 		}
 
-		write(uart, &buffer[i], 1);
+		write(uart, &buffer[i], sizeof(buffer[i]));
 
 		/* Sleep before sending the next byte. */
 		usleep(POST_WRITE_DELAY_IN_USECS);
@@ -190,13 +180,14 @@ int send_data(int uart, uint8_t *buffer, int size)
 	return OK;
 }
 
-int hott_telemetry_thread_main(int argc, char *argv[])
+int
+hott_telemetry_thread_main(int argc, char *argv[])
 {
-	INFO_MSG("starting");
+	warnx("starting");
 
 	thread_running = true;
 
-	char *device = "/dev/ttyS1";		/**< Default telemetry port: USART2 */
+	const char *device = "/dev/ttyS1";		/**< Default telemetry port: USART2 */
 
 	/* read commandline arguments */
 	for (int i = 0; i < argc && argv[i]; i++) {
@@ -206,45 +197,48 @@ int hott_telemetry_thread_main(int argc, char *argv[])
 
 			} else {
 				thread_running = false;
-				ERROR_MSG("missing parameter to -d");
-				ERROR_MSG(commandline_usage);
-				exit(1);
+				errx(1, "missing parameter to -d\n%s", commandline_usage);
 			}
 		}
 	}
 
 	/* enable UART, writes potentially an empty buffer, but multiplexing is disabled */
 	struct termios uart_config_original;
-	int uart = open_uart(device, &uart_config_original);
+	const int uart = open_uart(device, &uart_config_original);
 
 	if (uart < 0) {
-		ERROR_MSG("Failed opening HoTT UART, exiting.");
+		errx(1, "Failed opening HoTT UART, exiting.");
 		thread_running = false;
-		exit(ERROR);
 	}
 
 	messages_init();
 
 	uint8_t buffer[MESSAGE_BUFFER_SIZE];
-	int size = 0;
-	int id = 0;
+	size_t size = 0;
+	uint8_t id = 0;
 
 	while (!thread_should_exit) {
-		if (read_data(uart, &id) == OK) {
+		if (recv_req_id(uart, &id) == OK) {
 			switch (id) {
-			case ELECTRIC_AIR_MODULE:
+			case EAM_SENSOR_ID:
 				build_eam_response(buffer, &size);
 				break;
 
+			case GPS_SENSOR_ID:
+				build_gps_response(buffer, &size);
+				break;
+
 			default:
 				continue;	// Not a module we support.
 			}
 
 			send_data(uart, buffer, size);
+		} else {
+			warnx("NOK");
 		}
 	}
 
-	INFO_MSG("exiting");
+	warnx("exiting");
 
 	close(uart);
 
@@ -256,23 +250,22 @@ int hott_telemetry_thread_main(int argc, char *argv[])
 /**
  * Process command line arguments and tart the daemon.
  */
-int hott_telemetry_main(int argc, char *argv[])
+int
+hott_telemetry_main(int argc, char *argv[])
 {
 	if (argc < 1) {
-		ERROR_MSG("missing command");
-		ERROR_MSG(commandline_usage);
-		exit(1);
+		errx(1, "missing command\n%s", commandline_usage);
 	}
 
 	if (!strcmp(argv[1], "start")) {
 
 		if (thread_running) {
-			INFO_MSG("deamon already running");
+			warnx("deamon already running");
 			exit(0);
 		}
 
 		thread_should_exit = false;
-		deamon_task = task_spawn("hott_telemetry",
+		deamon_task = task_spawn(daemon_name,
 					 SCHED_DEFAULT,
 					 SCHED_PRIORITY_MAX - 40,
 					 2048,
@@ -288,19 +281,14 @@ int hott_telemetry_main(int argc, char *argv[])
 
 	if (!strcmp(argv[1], "status")) {
 		if (thread_running) {
-			INFO_MSG("daemon is running");
+			warnx("daemon is running");
 
 		} else {
-			INFO_MSG("daemon not started");
+			warnx("daemon not started");
 		}
 
 		exit(0);
 	}
 
-	ERROR_MSG("unrecognized command");
-	ERROR_MSG(commandline_usage);
-	exit(1);
+	errx(1, "unrecognized command\n%s", commandline_usage);
 }
-
-
-
diff --git a/src/drivers/hott_telemetry/messages.c b/src/drivers/hott_telemetry/messages.c
index f0f32d244..369070f8c 100644
--- a/src/drivers/hott_telemetry/messages.c
+++ b/src/drivers/hott_telemetry/messages.c
@@ -1,7 +1,7 @@
 /****************************************************************************
  *
- *   Copyright (c) 2012, 2013 PX4 Development Team. All rights reserved.
- *   Author: Simon Wilks <sjwilks@gmail.com>
+ *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+ *   Author: @author Simon Wilks <sjwilks@gmail.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -34,30 +34,44 @@
 
 /**
  * @file messages.c
- * @author Simon Wilks <sjwilks@gmail.com>
+ *
  */
 
 #include "messages.h"
 
+#include <math.h>
+#include <stdio.h>
 #include <string.h>
-#include <systemlib/systemlib.h>
+#include <systemlib/geo/geo.h>
 #include <unistd.h>
-#include <uORB/topics/airspeed.h>
 #include <uORB/topics/battery_status.h>
+#include <uORB/topics/home_position.h>
 #include <uORB/topics/sensor_combined.h>
+#include <uORB/topics/vehicle_gps_position.h>
+
+/* The board is very roughly 5 deg warmer than the surrounding air */
+#define BOARD_TEMP_OFFSET_DEG 5
 
-static int airspeed_sub = -1;
 static int battery_sub = -1;
+static int gps_sub = -1;
+static int home_sub = -1;
 static int sensor_sub = -1;
 
-void messages_init(void)
+static bool home_position_set = false;
+static double home_lat = 0.0d;
+static double home_lon = 0.0d;
+
+void 
+messages_init(void)
 {
 	battery_sub = orb_subscribe(ORB_ID(battery_status));
+	gps_sub = orb_subscribe(ORB_ID(vehicle_gps_position));
+	home_sub = orb_subscribe(ORB_ID(home_position));
 	sensor_sub = orb_subscribe(ORB_ID(sensor_combined));
-	airspeed_sub = orb_subscribe(ORB_ID(airspeed));
 }
 
-void build_eam_response(uint8_t *buffer, int *size)
+void 
+build_eam_response(uint8_t *buffer, size_t *size)
 {
 	/* get a local copy of the current sensor values */
 	struct sensor_combined_s raw;
@@ -74,26 +88,144 @@ void build_eam_response(uint8_t *buffer, int *size)
 	memset(&msg, 0, *size);
 
 	msg.start = START_BYTE;
-	msg.eam_sensor_id = ELECTRIC_AIR_MODULE;
-	msg.sensor_id = EAM_SENSOR_ID;
+	msg.eam_sensor_id = EAM_SENSOR_ID;
+	msg.sensor_id = EAM_SENSOR_TEXT_ID;
+	
 	msg.temperature1 = (uint8_t)(raw.baro_temp_celcius + 20);
-	msg.temperature2 = TEMP_ZERO_CELSIUS;
+	msg.temperature2 = msg.temperature1 - BOARD_TEMP_OFFSET_DEG;
+
 	msg.main_voltage_L = (uint8_t)(battery.voltage_v * 10);
 
 	uint16_t alt = (uint16_t)(raw.baro_alt_meter + 500);
 	msg.altitude_L = (uint8_t)alt & 0xff;
 	msg.altitude_H = (uint8_t)(alt >> 8) & 0xff;
 
+	msg.stop = STOP_BYTE;
+	memcpy(buffer, &msg, *size);
+}
+
+void 
+build_gps_response(uint8_t *buffer, size_t *size)
+{
 	/* get a local copy of the current sensor values */
-	struct airspeed_s airspeed;
-	memset(&airspeed, 0, sizeof(airspeed));
-	orb_copy(ORB_ID(airspeed), airspeed_sub, &airspeed);
+	struct sensor_combined_s raw;
+	memset(&raw, 0, sizeof(raw));
+	orb_copy(ORB_ID(sensor_combined), sensor_sub, &raw);
 
-	uint16_t speed = (uint16_t)(airspeed.indicated_airspeed_m_s * 3.6);
-	msg.speed_L = (uint8_t)speed & 0xff;
-	msg.speed_H = (uint8_t)(speed >> 8) & 0xff;
+ 	/* get a local copy of the battery data */
+	struct vehicle_gps_position_s gps;
+	memset(&gps, 0, sizeof(gps));
+	orb_copy(ORB_ID(vehicle_gps_position), gps_sub, &gps);
 
-	msg.stop = STOP_BYTE;
+	struct gps_module_msg msg = { 0 };
+	*size = sizeof(msg);
+	memset(&msg, 0, *size);
+
+	msg.start = START_BYTE;
+	msg.sensor_id = GPS_SENSOR_ID;
+	msg.sensor_text_id = GPS_SENSOR_TEXT_ID;
+
+	msg.gps_num_sat = gps.satellites_visible;
+
+	/* The GPS fix type: 0 = none, 2 = 2D, 3 = 3D */
+	msg.gps_fix_char = (uint8_t)(gps.fix_type + 48);
+	msg.gps_fix = (uint8_t)(gps.fix_type + 48);
 
+	/* No point collecting more data if we don't have a 3D fix yet */
+	if (gps.fix_type > 2) {
+		/* Current flight direction */
+		msg.flight_direction = (uint8_t)(gps.cog_rad * M_RAD_TO_DEG_F);
+
+		/* GPS speed */
+		uint16_t speed = (uint16_t)(gps.vel_m_s * 3.6);
+		msg.gps_speed_L = (uint8_t)speed & 0xff;
+		msg.gps_speed_H = (uint8_t)(speed >> 8) & 0xff;
+		
+		/* Get latitude in degrees, minutes and seconds */
+		double lat = ((double)(gps.lat))*1e-7d;
+
+		/* Set the N or S specifier */		
+		msg.latitude_ns = 0;
+		if (lat < 0) {
+			msg.latitude_ns = 1;
+			lat = abs(lat);
+		}
+
+		int deg;
+		int min;
+		int sec;
+		convert_to_degrees_minutes_seconds(lat, &deg, &min, &sec);
+
+		uint16_t lat_min = (uint16_t)(deg * 100 + min);
+		msg.latitude_min_L = (uint8_t)lat_min & 0xff;
+		msg.latitude_min_H = (uint8_t)(lat_min >> 8) & 0xff;
+		uint16_t lat_sec = (uint16_t)(sec);
+		msg.latitude_sec_L = (uint8_t)lat_sec & 0xff;
+		msg.latitude_sec_H = (uint8_t)(lat_sec >> 8) & 0xff;
+
+		/* Get longitude in degrees, minutes and seconds */
+		double lon = ((double)(gps.lon))*1e-7d;
+
+		/* Set the E or W specifier */
+		msg.longitude_ew = 0;
+		if (lon < 0) {
+			msg.longitude_ew = 1;
+			lon = abs(lon);
+		}
+
+		convert_to_degrees_minutes_seconds(lon, &deg, &min, &sec);
+		
+		uint16_t lon_min = (uint16_t)(deg * 100 + min);
+		msg.longitude_min_L = (uint8_t)lon_min & 0xff;
+		msg.longitude_min_H = (uint8_t)(lon_min >> 8) & 0xff;
+		uint16_t lon_sec = (uint16_t)(sec);
+		msg.longitude_sec_L = (uint8_t)lon_sec & 0xff;
+		msg.longitude_sec_H = (uint8_t)(lon_sec >> 8) & 0xff;
+		
+		/* Altitude */
+		uint16_t alt = (uint16_t)(gps.alt*1e-3 + 500.0f);
+		msg.altitude_L = (uint8_t)alt & 0xff;
+		msg.altitude_H = (uint8_t)(alt >> 8) & 0xff;
+
+		/* Get any (and probably only ever one) home_sub postion report */
+		bool updated;
+		orb_check(home_sub, &updated);
+		if (updated) {
+			/* get a local copy of the home position data */
+			struct home_position_s home;
+			memset(&home, 0, sizeof(home));
+			orb_copy(ORB_ID(home_position), home_sub, &home);
+
+			home_lat = ((double)(home.lat))*1e-7d;
+			home_lon = ((double)(home.lon))*1e-7d;
+			home_position_set = true;
+		}
+
+		/* Distance from home */
+		if (home_position_set) {
+			uint16_t dist = (uint16_t)get_distance_to_next_waypoint(home_lat, home_lon, lat, lon);
+
+			msg.distance_L = (uint8_t)dist & 0xff;
+			msg.distance_H = (uint8_t)(dist >> 8) & 0xff;
+
+			/* Direction back to home */
+			uint16_t bearing = (uint16_t)(get_bearing_to_next_waypoint(home_lat, home_lon, lat, lon) * M_RAD_TO_DEG_F);
+			msg.home_direction = (uint8_t)bearing >> 1;
+		}
+	}
+
+	msg.stop = STOP_BYTE;
 	memcpy(buffer, &msg, *size);
-}
\ No newline at end of file
+}
+
+void
+convert_to_degrees_minutes_seconds(double val, int *deg, int *min, int *sec)
+{
+	*deg = (int)val;
+
+	double delta = val - *deg;
+	const double min_d = delta * 60.0d;
+	*min = (int)min_d;
+	delta = min_d - *min;
+	*sec = (int)(delta * 10000.0d);
+}
diff --git a/src/drivers/hott_telemetry/messages.h b/src/drivers/hott_telemetry/messages.h
index dd38075fa..e6d5cc723 100644
--- a/src/drivers/hott_telemetry/messages.h
+++ b/src/drivers/hott_telemetry/messages.h
@@ -44,11 +44,6 @@
 
 #include <stdlib.h>
 
-/* The buffer size used to store messages. This must be at least as big as the number of
- * fields in the largest message struct.
- */
-#define MESSAGE_BUFFER_SIZE 50
-
 /* The HoTT receiver demands a minimum 5ms period of silence after delivering its request.
  * Note that the value specified here is lower than 5000 (5ms) as time is lost constucting
  * the message after the read which takes some milliseconds.
@@ -66,18 +61,18 @@
 #define TEMP_ZERO_CELSIUS	0x14
 
 /* Electric Air Module (EAM) constants. */
-#define ELECTRIC_AIR_MODULE	0x8e
-#define EAM_SENSOR_ID		0xe0
+#define EAM_SENSOR_ID			0x8e
+#define EAM_SENSOR_TEXT_ID		0xe0
 
 /* The Electric Air Module message. */
 struct eam_module_msg {
-	uint8_t start;			/**< Start byte   				*/
-	uint8_t eam_sensor_id;		/**< EAM sensor ID 				*/
+	uint8_t start;				/**< Start byte   				*/
+	uint8_t eam_sensor_id;		/**< EAM sensor					*/
 	uint8_t warning;
-	uint8_t sensor_id;		/**< Sensor ID, why different? 			*/
+	uint8_t sensor_id;			/**< Sensor ID, why different?	*/
 	uint8_t alarm_inverse1;
 	uint8_t alarm_inverse2;
-	uint8_t cell1_L;		/**< Lipo cell voltages. Not supported. 	*/
+	uint8_t cell1_L;			/**< Lipo cell voltages. Not supported.	*/
 	uint8_t cell2_L;
 	uint8_t cell3_L;
 	uint8_t cell4_L;
@@ -95,30 +90,107 @@ struct eam_module_msg {
 	uint8_t batt1_voltage_H;
 	uint8_t batt2_voltage_L;	/**< Battery 2 voltage, lower 8-bits in steps of 0.02V 	*/
 	uint8_t batt2_voltage_H;
-	uint8_t temperature1;		/**< Temperature sensor 1. 20 = 0 degrees 		*/
+	uint8_t temperature1;		/**< Temperature sensor 1. 20 = 0 degrees */
 	uint8_t temperature2;
-	uint8_t altitude_L;		/**< Attitude (meters) lower 8-bits. 500 = 0 meters 	*/
+	uint8_t altitude_L;			/**< Attitude (meters) lower 8-bits. 500 = 0 meters */
 	uint8_t altitude_H;
-	uint8_t current_L;		/**< Current (mAh) lower 8-bits in steps of 0.1V 	*/
+	uint8_t current_L;			/**< Current (mAh) lower 8-bits in steps of 0.1V */
 	uint8_t current_H;
-	uint8_t main_voltage_L;		/**< Main power voltage lower 8-bits in steps of 0.1V 	*/
+	uint8_t main_voltage_L;		/**< Main power voltage lower 8-bits in steps of 0.1V */
 	uint8_t main_voltage_H;
-	uint8_t battery_capacity_L;	/**< Used battery capacity in steps of 10mAh 		*/
+	uint8_t battery_capacity_L;	/**< Used battery capacity in steps of 10mAh */
 	uint8_t battery_capacity_H;
-	uint8_t climbrate_L;		/**< Climb rate in 0.01m/s. 0m/s = 30000 		*/
+	uint8_t climbrate_L;		/**< Climb rate in 0.01m/s. 0m/s = 30000 */
 	uint8_t climbrate_H;
-	uint8_t climbrate_3s;		/**< Climb rate in m/3sec. 0m/3sec = 120 		*/
-	uint8_t rpm_L;			/**< RPM Lower 8-bits In steps of 10 U/min 		*/
+	uint8_t climbrate_3s;		/**< Climb rate in m/3sec. 0m/3sec = 120 */
+	uint8_t rpm_L;				/**< RPM Lower 8-bits In steps of 10 U/min */
 	uint8_t rpm_H;
-	uint8_t electric_min;		/**< Flight time in minutes. 				*/
-	uint8_t electric_sec;		/**< Flight time in seconds. 				*/
-	uint8_t speed_L;		/**< Airspeed in km/h in steps of 1 km/h 		*/
+	uint8_t electric_min;		/**< Flight time in minutes. */
+	uint8_t electric_sec;		/**< Flight time in seconds. */
+	uint8_t speed_L;			/**< Airspeed in km/h in steps of 1 km/h */
 	uint8_t speed_H;
-	uint8_t stop;			/**< Stop byte 						*/
-	uint8_t checksum;		/**< Lower 8-bits of all bytes summed. 			*/
+	uint8_t stop;				/**< Stop byte */
+	uint8_t checksum;			/**< Lower 8-bits of all bytes summed. */
 };
 
+/** 
+ * The maximum buffer size required to store a HoTT message.
+ */
+#define MESSAGE_BUFFER_SIZE sizeof(union { 	\
+    struct eam_module_msg eam; 				\
+})
+
+/* GPS sensor constants. */
+#define GPS_SENSOR_ID		0x8A
+#define GPS_SENSOR_TEXT_ID	0xA0
+
+/** 
+ * The GPS sensor message
+ * Struct based on: https://code.google.com/p/diy-hott-gps/downloads 
+ */
+struct gps_module_msg { 
+	uint8_t start;				/**< Start byte */
+	uint8_t sensor_id;			/**< GPS sensor ID*/
+	uint8_t warning;			/**< Byte 3: 0…= warning beeps */
+	uint8_t sensor_text_id;		/**< GPS Sensor text mode ID */
+	uint8_t alarm_inverse1;		/**< Byte 5: 01 inverse status */
+	uint8_t alarm_inverse2;		/**< Byte 6: 00 inverse status status 1 = no GPS Signal */
+	uint8_t flight_direction;	/**< Byte 7: 119 = Flightdir./dir. 1 = 2°; 0° (North), 9 0° (East), 180° (South), 270° (West) */
+	uint8_t gps_speed_L;		/**< Byte 8: 8 = /GPS speed low byte 8km/h */
+	uint8_t gps_speed_H;		/**< Byte 9: 0 = /GPS speed high byte */
+	  
+	uint8_t latitude_ns;		/**< Byte 10: 000 = N = 48°39’988 */
+	uint8_t latitude_min_L;		/**< Byte 11: 231 0xE7 = 0x12E7 = 4839 */
+	uint8_t latitude_min_H;		/**< Byte 12: 018 18 = 0x12 */
+	uint8_t latitude_sec_L;		/**< Byte 13: 171 220 = 0xDC = 0x03DC =0988 */
+	uint8_t latitude_sec_H;		/**< Byte 14: 016 3 = 0x03 */
+	 
+	uint8_t longitude_ew;		/**< Byte 15: 000  = E= 9° 25’9360 */
+	uint8_t longitude_min_L;	/**< Byte 16: 150 157 = 0x9D = 0x039D = 0925 */
+	uint8_t longitude_min_H;	/**< Byte 17: 003 3 = 0x03 */
+	uint8_t longitude_sec_L;	/**< Byte 18: 056 144 = 0x90 0x2490 = 9360*/
+	uint8_t longitude_sec_H;	/**< Byte 19: 004 36 = 0x24 */
+	  
+	uint8_t distance_L;			/**< Byte 20: 027 123 = /distance low byte 6 = 6 m */
+	uint8_t distance_H;			/**< Byte 21: 036 35 = /distance high byte */
+	uint8_t altitude_L;			/**< Byte 22: 243 244 = /Altitude low byte 500 = 0m */
+	uint8_t altitude_H;			/**< Byte 23: 001 1 = /Altitude high byte */
+	uint8_t resolution_L;		/**< Byte 24: 48 = Low Byte m/s resolution 0.01m 48 = 30000 = 0.00m/s (1=0.01m/s) */
+	uint8_t resolution_H;		/**< Byte 25: 117 = High Byte m/s resolution 0.01m */
+	uint8_t unknown1;			/**< Byte 26: 120 = 0m/3s */
+	uint8_t gps_num_sat;		/**< Byte 27: GPS.Satellites (number of satelites) (1 byte) */
+	uint8_t gps_fix_char;		/**< Byte 28: GPS.FixChar. (GPS fix character. display, if DGPS, 2D oder 3D) (1 byte) */
+	uint8_t home_direction;		/**< Byte 29: HomeDirection (direction from starting point to Model position) (1 byte) */
+	uint8_t angle_x_direction;	/**< Byte 30: angle x-direction (1 byte) */
+	uint8_t angle_y_direction;	/**< Byte 31: angle y-direction (1 byte) */
+	uint8_t angle_z_direction;	/**< Byte 32: angle z-direction (1 byte) */
+	uint8_t gyro_x_L;			/**< Byte 33: gyro x low byte (2 bytes) */
+	uint8_t gyro_x_H;			/**< Byte 34: gyro x high byte */
+	uint8_t gyro_y_L;			/**< Byte 35: gyro y low byte (2 bytes) */
+	uint8_t gyro_y_H;			/**< Byte 36: gyro y high byte */
+	uint8_t gyro_z_L;			/**< Byte 37: gyro z low byte (2 bytes) */
+	uint8_t gyro_z_H;			/**< Byte 38: gyro z high byte */
+	uint8_t vibration;			/**< Byte 39: vibration (1 bytes) */
+	uint8_t ascii4;				/**< Byte 40: 00 ASCII Free Character [4] */
+	uint8_t ascii5;				/**< Byte 41: 00 ASCII Free Character [5] */
+	uint8_t gps_fix;			/**< Byte 42: 00 ASCII Free Character [6], we use it for GPS FIX */
+	uint8_t version;			/**< Byte 43: 00 version number */
+	uint8_t stop;				/**< Byte 44: 0x7D Ende byte */
+	uint8_t checksum;			/**< Byte 45: Parity Byte */
+};
+
+/** 
+ * The maximum buffer size required to store a HoTT message.
+ */
+#define GPS_MESSAGE_BUFFER_SIZE sizeof(union { 	\
+    struct gps_module_msg gps; 				\
+})
+
 void messages_init(void);
-void build_eam_response(uint8_t *buffer, int *size);
+void build_eam_response(uint8_t *buffer, size_t *size);
+void build_gps_response(uint8_t *buffer, size_t *size);
+float _get_distance_to_next_waypoint(double lat_now, double lon_now, double lat_next, double lon_next);
+void convert_to_degrees_minutes_seconds(double lat, int *deg, int *min, int *sec);
+
 
 #endif /* MESSAGES_H_ */