ardupilot/libraries/AP_GPS/AP_GPS_Auto.cpp

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

/// @file	AP_GPS_Auto.cpp
/// @brief	Simple GPS auto-detection logic.

#include <FastSerial.h>
#include <AP_Common.h>

#include "AP_GPS.h"		// includes AP_GPS_Auto.h

// Define this to add NMEA to the auto-detection cycle.
//
// Note that there is a potential race where NMEA data may overlap with
// the commands that switch a GPS out of NMEA mode that can cause
// the GPS to switch to binary mode at the same time that this code
// detects it as being in NMEA mode.
//
//#define WITH_NMEA_MODE	1

static unsigned int	baudrates[] = {38400U, 57600U, 9600U, 4800U};

const prog_char	AP_GPS_Auto::_mtk_set_binary[]   PROGMEM = MTK_SET_BINARY;
const prog_char	AP_GPS_Auto::_ublox_set_binary[] PROGMEM = UBLOX_SET_BINARY;
const prog_char	AP_GPS_Auto::_sirf_set_binary[]  PROGMEM = SIRF_SET_BINARY;


AP_GPS_Auto::AP_GPS_Auto(FastSerial *s, GPS **gps)  :
	GPS(s),
	_fs(s),
	_gps(gps)
{
}

// Do nothing at init time - it may be too early to try detecting the GPS
//
void
AP_GPS_Auto::init(void)
{
}

// Called the first time that a client tries to kick the GPS to update.
//
// We detect the real GPS, then update the pointer we have been called through
// and return.
//
/// @todo	This routine spends a long time trying to detect a GPS.  That's not strictly
///			desirable; it might be a good idea to rethink the logic here to make it
///			more asynchronous, so that other parts of the system can get a chance
///			to run while GPS detection is in progress.
///
bool
AP_GPS_Auto::read(void)
{
	GPS		*gps;
	int		i;
	unsigned long then;

	// Loop through possible baudrates trying to detect a GPS at one of them.
	//
	// Note that we need to have a FastSerial rather than a Stream here because
	// Stream has no idea of line speeds.  FastSerial is quite OK with us calling
	// ::begin any number of times.
	//
	for (i = 0; i < (sizeof(baudrates) / sizeof(baudrates[0])); i++) {

		_fs->begin(baudrates[i]);
		if (NULL != (gps = _detect())) {

			// configure the detected GPS and give it a chance to listen to its device
			gps->init();
			then = millis();
			while ((millis() - then) < 1200) {
				// if we get a successful update from the GPS, we are done
				gps->new_data = false;
				gps->update();
				if (gps->new_data) {
					Serial.println_P(PSTR("OK"));
					*_gps = gps;
					return true;
				}
			}
			// GPS driver failed to parse any data from GPS,
			// delete the driver and continue the process.
			Serial.println_P(PSTR("failed, retrying"));
			delete gps;
		}
	}
}

//
// Perform one iteration of the auto-detection process.
//
GPS *
AP_GPS_Auto::_detect(void)
{
	unsigned long then;
	int		fingerprint[4];
	int		tries;
	GPS		*gps;

	//
	// Loop attempting to detect a recognized GPS
	//
	Serial.print('G');
	gps = NULL;
	for (tries = 0; tries < 2; tries++) {

		//
		// Empty the serial buffer and wait for 50ms of quiet.
		//
		// XXX We can detect babble by counting incoming characters, but
		//     what would we do about it?
		//
		_port->flush();
		then = millis();
		do {
			if (_port->available()) {
				then = millis();
				_port->read();
			}
		} while ((millis() - then) < 50);

		//
		// Collect four characters to fingerprint a device
		//
		// If we take more than 1200ms to receive four characters, abort.
		// This will normally only be the case where there is no GPS attached.
		//
		while (_port->available() < 4) {
			if ((millis() - then) > 1200) {
				Serial.print('!');
				return NULL;
			}
		}
		fingerprint[0] = _port->read();
		fingerprint[1] = _port->read();
		fingerprint[2] = _port->read();
		fingerprint[3] = _port->read();

		//
		// ublox or MTK in DIYD binary mode (whose smart idea was
		// it to make the MTK look sort-of like it was talking UBX?)
		//
		if ((0xb5 == fingerprint[0]) &&
			(0x62 == fingerprint[1]) &&
			(0x01 == fingerprint[2])) {

			// message 5 is MTK pretending to talk UBX
			if (0x05 == fingerprint[3]) {
				gps = new AP_GPS_MTK(_port);
				Serial.print_P(PSTR(" MTK1.4 "));
				break;
			}

			// any other message is ublox
			gps = new AP_GPS_UBLOX(_port);
			Serial.print_P(PSTR(" ublox "));
			break;
		}

		//
		// MTK v1.6
		//
		if ((0xd0 == fingerprint[0]) &&
			(0xdd == fingerprint[1]) &&
			(0x20 == fingerprint[2])) {
			gps = new AP_GPS_MTK16(_port);
			Serial.print_P(PSTR(" MTK1.6 "));
			break;
		}

		//
		// SIRF in binary mode
		//
		if ((0xa0 == fingerprint[0]) &&
			(0xa2 == fingerprint[1])) {
			gps = new AP_GPS_SIRF(_port);
			Serial.print_P(PSTR(" SiRF "));
			break;
		}

		//
		// If we haven't spammed the various init strings, send them now
		// and retry to avoid a false-positive on the NMEA detector.
		//
		if (0 == tries) {
			Serial.print('*');
			// use the FastSerial port handle so that we can use PROGMEM strings
			_fs->println_P(_mtk_set_binary);
			_fs->println_P(_ublox_set_binary);
			_fs->println_P(_sirf_set_binary);

			// give the GPS time to react to the settings
			delay(100);
			continue;
		} else {
			Serial.print('?');
		}

#if WITH_NMEA_MODE
		//
		// Something talking NMEA
		//
		if (('$' == fingerprint[0]) &&
			(('G' == fingerprint[1]) || ('P' == fingerprint[1]))) {

			// XXX this may be a bit presumptive, might want to give the GPS a couple of
			//     iterations around the loop to react to init strings?
			gps = new AP_GPS_NMEA(_port);
			break;
		}
#endif
	}
	return(gps);
}