ardupilot/libraries/AP_GPS/AP_GPS_MTK16.cpp

134 lines
3.5 KiB
C++

// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: t -*-
//
// DIYDrones Custom Mediatek GPS driver for ArduPilot and ArduPilotMega.
// Code by Michael Smith, Jordi Munoz and Jose Julio, DIYDrones.com
//
// This library is free software; you can redistribute it and / or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// GPS configuration : Custom protocol per "DIYDrones Custom Binary Sentence Specification V1.1"
//
#include "AP_GPS_MTK16.h"
#include <stdint.h>
// Constructors ////////////////////////////////////////////////////////////////
AP_GPS_MTK16::AP_GPS_MTK16(Stream *s) : GPS(s)
{
}
// Public Methods //////////////////////////////////////////////////////////////
void
AP_GPS_MTK16::init(void)
{
_port->flush();
// initialize serial port for binary protocol use
// XXX should assume binary, let GPS_AUTO handle dynamic config?
_port->print(MTK_SET_BINARY);
// set 4Hz update rate
_port->print(MTK_OUTPUT_4HZ);
}
// Process bytes available from the stream
//
// The stream is assumed to contain only our custom message. If it
// contains other messages, and those messages contain the preamble bytes,
// it is possible for this code to become de-synchronised. Without
// buffering the entire message and re-processing it from the top,
// this is unavoidable.
//
// The lack of a standard header length field makes it impossible to skip
// unrecognised messages.
//
bool
AP_GPS_MTK16::read(void)
{
uint8_t data;
int numc;
bool parsed = false;
numc = _port->available();
for (int i = 0; i < numc; i++) { // Process bytes received
// read the next byte
data = _port->read();
restart:
switch(_step){
// Message preamble, class, ID detection
//
// If we fail to match any of the expected bytes, we
// reset the state machine and re-consider the failed
// byte as the first byte of the preamble. This
// improves our chances of recovering from a mismatch
// and makes it less likely that we will be fooled by
// the preamble appearing as data in some other message.
//
case 0:
if(PREAMBLE1 == data)
_step++;
break;
case 1:
if (PREAMBLE2 == data) {
_step++;
break;
}
_step = 0;
goto restart;
case 2:
if (sizeof(_buffer) == data) {
_step++;
_ck_b = _ck_a = data; // reset the checksum accumulators
_payload_counter = 0;
} else {
_step = 0; // reset and wait for a message of the right class
goto restart;
}
break;
// Receive message data
//
case 3:
_buffer.bytes[_payload_counter++] = data;
_ck_b += (_ck_a += data);
if (_payload_counter == sizeof(_buffer))
_step++;
break;
// Checksum and message processing
//
case 4:
_step++;
if (_ck_a != data) {
_step = 0;
}
break;
case 5:
_step = 0;
if (_ck_b != data) {
break;
}
fix = _buffer.msg.fix_type == FIX_3D;
latitude = _buffer.msg.latitude * 10; // XXX doc says *10e7 but device says otherwise
longitude = _buffer.msg.longitude * 10; // XXX doc says *10e7 but device says otherwise
altitude = _buffer.msg.altitude;
ground_speed = _buffer.msg.ground_speed;
ground_course = _buffer.msg.ground_course;
num_sats = _buffer.msg.satellites;
hdop = _buffer.msg.hdop;
// XXX docs say this is UTC, but our clients expect msToW
time = _swapl(&_buffer.msg.utc_time);
parsed = true;
}
}
return parsed;
}