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