ardupilot/libraries/AP_GPS/GPS.h

// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-

/// @file	GPS.h
/// @brief	Interface definition for the various GPS drivers.

#ifndef GPS_h
#define GPS_h

#include <inttypes.h>
#include <Stream.h>

/// @class	GPS
/// @brief	Abstract base class for GPS receiver drivers.
class GPS
{
public:

	/// Update GPS state based on possible bytes received from the module.
	///
	/// This routine must be called periodically to process incoming data.
	///
	/// GPS drivers should not override this function; they should implement
	/// ::read instead.
	///
	void			update(void);

	/// GPS status codes
	///
	/// \note Non-intuitive ordering for legacy reasons
	///
	enum GPS_Status {
		NO_GPS = 0,		///< No GPS connected/detected 
		NO_FIX = 1,		///< Receiving valid GPS messages but no lock 
		GPS_OK = 2		///< Receiving valid messages and locked
	};

	/// Query GPS status
	///
	/// The 'valid message' status indicates that a recognised message was
	/// received from the GPS within the last 500ms.
	///
	/// @returns			Current GPS status
	///
	GPS_Status		status(void) { return _status; }

	/// Startup initialisation.
	///
	/// This routine performs any one-off initialisation required to set the
	/// GPS up for use.
	///
	/// Must be implemented by the GPS driver.
	///
	virtual void	init(void) = 0;

	// Properties
	long	time;			///< GPS time in milliseconds from the start of the week
	long	latitude;		///< latitude in degrees * 10,000,000
	long	longitude;		///< longitude in degrees * 10,000,000
	long	altitude;		///< altitude in cm
	long	ground_speed;	///< ground speed in cm/sec
	long	ground_course;	///< ground course in 100ths of a degree
	long	speed_3d;		///< 3D speed in cm/sec (not always available)
	int		hdop;			///< horizontal dilution of precision in cm
	uint8_t num_sats;		///< Number of visible satelites

	/// Set to true when new data arrives.  A client may set this
	/// to false in order to avoid processing data they have
	/// already seen.
	bool	new_data;

	// Deprecated properties
	bool	fix;			///< true if we have a position fix (use ::status instead)
	bool	valid_read;		///< true if we have seen data from the GPS (use ::status instead)

	// Debug support
	bool	print_errors; 	///< deprecated

protected:
	Stream	*_port;			///< port the GPS is attached to

	/// Constructor
	///
	/// @note The stream is expected to be set up and configured for the
	///       correct bitrate before ::init is called.
	///
	/// @param	s	Stream connected to the GPS module.  
	///
	GPS(Stream *s) : _port(s) {};

	/// read from the GPS stream and update properties
	///
	/// Must be implemented by the GPS driver.
	///
	/// @returns			true if a valid message was received from the GPS
	///
	virtual bool	read(void) = 0;

	/// perform an endian swap on a long
	///
	/// @param	bytes		pointer to a buffer containing bytes representing a
	///						long in the wrong byte order
	/// @returns			endian-swapped value
	///
	long			_swapl(const void *bytes);

	/// perform an endian swap on an int
	///
	/// @param	bytes		pointer to a buffer containing bytes representing an
	///						int in the wrong byte order
	///	@returns			endian-swapped value
	int				_swapi(const void *bytes);

	/// emit an error message
	///
	/// based on the value of print_errors, emits the printf-formatted message
	/// in msg,... to stderr
	///
	/// @param	fmt			printf-like format string
	///
	/// @note deprecated as-is due to the difficulty of hooking up to a working
	///       printf vs. the potential benefits
	///
	void			_error(const char *msg);

private:

	/// Time in milliseconds after which we will assume the GPS is no longer
	/// sending us updates and attempt a re-init.
	///
	static const unsigned long	_idleTimeout = 500;

	/// Last time that the GPS driver got a good packet from the GPS
	///
	unsigned long 				_idleTimer;

	/// Our current status
	GPS_Status					_status;
};

inline long
GPS::_swapl(const void *bytes)
{
	const uint8_t	*b = (const uint8_t *)bytes;
	union {
		long	v;
		uint8_t b[4];
	} u;

	u.b[0] = b[3];
	u.b[1] = b[2];
	u.b[2] = b[1];
	u.b[3] = b[0];

	return(u.v);
}

inline int16_t
GPS::_swapi(const void *bytes)
{
	const uint8_t	*b = (const uint8_t *)bytes;
	union {
		int16_t	v;
		uint8_t b[2];
	} u;

	u.b[0] = b[1];
	u.b[1] = b[0];

	return(u.v);
}

#endif