ardupilot/libraries/AP_GPS/AP_GPS_MTK19.cpp

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// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
//
// DIYDrones Custom Mediatek GPS driver for ArduPilot and ArduPilotMega.
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// Code by Michael Smith, Jordi Munoz and Jose Julio, Craig Elder, DIYDrones.com
//
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// GPS configuration : Custom protocol per "DIYDrones Custom Binary Sentence Specification V1.6, v1.7, v1.8, v1.9"
//
// Note that this driver supports both the 1.6 and 1.9 protocol varients
//
#include "AP_GPS_MTK19.h"
extern const AP_HAL::HAL& hal;
AP_GPS_MTK19::AP_GPS_MTK19(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port) :
AP_GPS_Backend(_gps, _state, _port),
_step(0),
_payload_counter(0),
_mtk_revision(0),
_fix_counter(0)
{
AP_GPS_MTK::send_init_blob(_state.instance, _gps);
}
// 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_MTK19::read(void)
{
uint8_t data;
int16_t numc;
bool parsed = false;
numc = port->available();
for (int16_t i = 0; i < numc; i++) { // Process bytes received
// read the next byte
data = port->read();
restart:
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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:
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if (data == PREAMBLE1_V16) {
_mtk_revision = MTK_GPS_REVISION_V16;
_step++;
} else if (data == PREAMBLE1_V19) {
_mtk_revision = MTK_GPS_REVISION_V19;
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_step++;
}
break;
case 1:
if (data == PREAMBLE2) {
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_step++;
} else {
_step = 0;
goto restart;
}
break;
case 2:
if (sizeof(_buffer) == data) {
_step++;
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_ck_b = _ck_a = data; // reset the checksum accumulators
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_payload_counter = 0;
} else {
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_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) {
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_step = 0;
goto restart;
}
break;
case 5:
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_step = 0;
if (_ck_b != data) {
goto restart;
}
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// parse fix
if (_buffer.msg.fix_type == FIX_3D || _buffer.msg.fix_type == FIX_3D_SBAS) {
state.status = AP_GPS::GPS_OK_FIX_3D;
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}else if (_buffer.msg.fix_type == FIX_2D || _buffer.msg.fix_type == FIX_2D_SBAS) {
state.status = AP_GPS::GPS_OK_FIX_2D;
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}else{
state.status = AP_GPS::NO_FIX;
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}
if (_mtk_revision == MTK_GPS_REVISION_V16) {
state.location.lat = _buffer.msg.latitude * 10; // V16, V17,V18 doc says *10e7 but device says otherwise
state.location.lng = _buffer.msg.longitude * 10; // V16, V17,V18 doc says *10e7 but device says otherwise
} else {
state.location.lat = _buffer.msg.latitude;
state.location.lng = _buffer.msg.longitude;
}
state.location.alt = _buffer.msg.altitude;
state.ground_speed = _buffer.msg.ground_speed*0.01f;
state.ground_course_cd = _buffer.msg.ground_course;
state.num_sats = _buffer.msg.satellites;
state.hdop = _buffer.msg.hdop;
if (state.status >= AP_GPS::GPS_OK_FIX_2D) {
if (_fix_counter == 0) {
uint32_t bcd_time_ms;
bcd_time_ms = _buffer.msg.utc_time;
#if 0
hal.console->printf("utc_date=%lu utc_time=%lu rev=%u\n",
(unsigned long)_buffer.msg.utc_date,
(unsigned long)_buffer.msg.utc_time,
(unsigned)_mtk_revision);
#endif
make_gps_time(_buffer.msg.utc_date, bcd_time_ms);
state.last_gps_time_ms = hal.scheduler->millis();
}
// the _fix_counter is to reduce the cost of the GPS
// BCD time conversion by only doing it every 10s
// between those times we use the HAL system clock as
// an offset from the last fix
_fix_counter++;
if (_fix_counter == 50) {
_fix_counter = 0;
}
}
fill_3d_velocity();
parsed = true;
}
}
return parsed;
}
/*
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detect a MTK16 or MTK19 GPS
*/
bool
AP_GPS_MTK19::_detect(struct MTK19_detect_state &state, uint8_t data)
{
restart:
switch (state.step) {
case 0:
state.ck_b = state.ck_a = state.payload_counter = 0;
if (data == PREAMBLE1_V16 || data == PREAMBLE1_V19) {
state.step++;
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}
break;
case 1:
if (PREAMBLE2 == data) {
state.step++;
} else {
state.step = 0;
goto restart;
}
break;
case 2:
if (data == sizeof(struct diyd_mtk_msg)) {
state.step++;
state.ck_b = state.ck_a = data;
} else {
state.step = 0;
goto restart;
}
break;
case 3:
state.ck_b += (state.ck_a += data);
if (++state.payload_counter == sizeof(struct diyd_mtk_msg))
state.step++;
break;
case 4:
state.step++;
if (state.ck_a != data) {
state.step = 0;
goto restart;
}
break;
case 5:
state.step = 0;
if (state.ck_b != data) {
goto restart;
}
return true;
}
return false;
}