ardupilot/libraries/AP_GPS/AP_GPS_MTK.cpp

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/*
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.
// Code by Michael Smith, Jordi Munoz and Jose Julio, DIYDrones.com
//
// GPS configuration : Custom protocol per "DIYDrones Custom Binary Sentence Specification V1.1"
//
#include "AP_GPS.h"
#include "AP_GPS_MTK.h"
// initialisation blobs to send to the GPS to try to get it into the
// right mode
const char AP_GPS_MTK::_initialisation_blob[] = MTK_OUTPUT_5HZ SBAS_ON WAAS_ON MTK_NAVTHRES_OFF;
AP_GPS_MTK::AP_GPS_MTK(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port) :
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AP_GPS_Backend(_gps, _state, _port)
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{
gps.send_blob_start(state.instance, _initialisation_blob, sizeof(_initialisation_blob));
}
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/*
send an initialisation blob to configure the GPS
*/
void AP_GPS_MTK::send_init_blob(uint8_t instance, AP_GPS &gps)
{
gps.send_blob_start(instance, _initialisation_blob, sizeof(_initialisation_blob));
}
// 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_MTK::read(void)
{
uint8_t data;
int16_t numc;
bool parsed = false;
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numc = port->available();
for (int16_t i = 0; i < numc; i++) { // Process bytes received
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// read the next byte
data = port->read();
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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.
//
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case 0:
if(PREAMBLE1 == data)
_step++;
break;
case 1:
if (PREAMBLE2 == data) {
_step++;
break;
}
_step = 0;
goto restart;
case 2:
if (MESSAGE_CLASS == data) {
_step++;
_ck_b = _ck_a = data; // reset the checksum accumulators
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} else {
_step = 0; // reset and wait for a message of the right class
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goto restart;
}
break;
case 3:
if (MESSAGE_ID == data) {
_step++;
_ck_b += (_ck_a += data);
_payload_counter = 0;
} else {
_step = 0;
goto restart;
}
break;
// Receive message data
//
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case 4:
_buffer[_payload_counter++] = data;
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_ck_b += (_ck_a += data);
if (_payload_counter == sizeof(_buffer))
_step++;
break;
// Checksum and message processing
//
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case 5:
_step++;
if (_ck_a != data) {
_step = 0;
}
break;
case 6:
_step = 0;
if (_ck_b != data) {
break;
}
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// set fix type
if (_buffer.msg.fix_type == FIX_3D) {
state.status = AP_GPS::GPS_OK_FIX_3D;
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}else if (_buffer.msg.fix_type == FIX_2D) {
state.status = AP_GPS::GPS_OK_FIX_2D;
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}else{
state.status = AP_GPS::NO_FIX;
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}
state.location.lat = swap_int32(_buffer.msg.latitude) * 10;
state.location.lng = swap_int32(_buffer.msg.longitude) * 10;
state.location.alt = swap_int32(_buffer.msg.altitude);
state.ground_speed = swap_int32(_buffer.msg.ground_speed) * 0.01f;
state.ground_course = wrap_360(swap_int32(_buffer.msg.ground_course) * 1.0e-6f);
state.num_sats = _buffer.msg.satellites;
if (state.status >= AP_GPS::GPS_OK_FIX_2D) {
make_gps_time(0, swap_int32(_buffer.msg.utc_time)*10);
}
// we don't change _last_gps_time as we don't know the
// full date
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fill_3d_velocity();
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parsed = true;
}
}
return parsed;
}
/*
detect a MTK GPS
*/
bool
AP_GPS_MTK::_detect(struct MTK_detect_state &state, uint8_t data)
{
switch (state.step) {
case 1:
if (PREAMBLE2 == data) {
state.step++;
break;
}
state.step = 0;
FALLTHROUGH;
case 0:
state.ck_b = state.ck_a = state.payload_counter = 0;
if(PREAMBLE1 == data)
state.step++;
break;
case 2:
if (MESSAGE_CLASS == data) {
state.step++;
state.ck_b = state.ck_a = data;
} else {
state.step = 0;
}
break;
case 3:
if (MESSAGE_ID == data) {
state.step++;
state.ck_b += (state.ck_a += data);
state.payload_counter = 0;
} else {
state.step = 0;
}
break;
case 4:
state.ck_b += (state.ck_a += data);
if (++state.payload_counter == sizeof(struct diyd_mtk_msg))
state.step++;
break;
case 5:
state.step++;
if (state.ck_a != data) {
state.step = 0;
}
break;
case 6:
state.step = 0;
if (state.ck_b == data) {
return true;
}
}
return false;
}