ardupilot/libraries/AP_GPS/GPS_Backend.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/>.
*/
#include <AP_GPS.h>
extern const AP_HAL::HAL& hal;
AP_GPS_Backend::AP_GPS_Backend(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port) :
port(_port),
gps(_gps),
state(_state)
{
}
int32_t AP_GPS_Backend::swap_int32(int32_t v) const
{
const uint8_t *b = (const uint8_t *)&v;
union {
int32_t v;
uint8_t b[4];
} u;
u.b[0] = b[3];
u.b[1] = b[2];
u.b[2] = b[1];
u.b[3] = b[0];
return u.v;
}
int16_t AP_GPS_Backend::swap_int16(int16_t v) const
{
const uint8_t *b = (const uint8_t *)&v;
union {
int16_t v;
uint8_t b[2];
} u;
u.b[0] = b[1];
u.b[1] = b[0];
return u.v;
}
/**
calculate current time since the unix epoch in microseconds
This costs about 60 usec on AVR2560
*/
uint64_t AP_GPS::time_epoch_usec(uint8_t instance)
{
const GPS_State &istate = state[instance];
if (istate.last_gps_time_ms == 0) {
return 0;
}
const uint64_t ms_per_week = 7000ULL*86400ULL;
const uint64_t unix_offset = 17000ULL*86400ULL + 52*10*7000ULL*86400ULL - 15000ULL;
uint64_t fix_time_ms = unix_offset + istate.time_week*ms_per_week + istate.time_week_ms;
// add in the milliseconds since the last fix
return (fix_time_ms + (hal.scheduler->millis() - istate.last_gps_time_ms)) * 1000ULL;
}
/**
fill in time_week_ms and time_week from BCD date and time components
assumes MTK19 millisecond form of bcd_time
This function takes about 340 usec on the AVR2560
*/
void AP_GPS_Backend::make_gps_time(uint32_t bcd_date, uint32_t bcd_milliseconds)
{
uint8_t year, mon, day, hour, min, sec;
uint16_t msec;
year = bcd_date % 100;
mon = (bcd_date / 100) % 100;
day = bcd_date / 10000;
uint32_t v = bcd_milliseconds;
msec = v % 1000; v /= 1000;
sec = v % 100; v /= 100;
min = v % 100; v /= 100;
hour = v % 100; v /= 100;
int8_t rmon = mon - 2;
if (0 >= rmon) {
rmon += 12;
year -= 1;
}
// get time in seconds since unix epoch
uint32_t ret = (year/4) - 15 + 367*rmon/12 + day;
ret += year*365 + 10501;
ret = ret*24 + hour;
ret = ret*60 + min;
ret = ret*60 + sec;
// convert to time since GPS epoch
ret -= 272764785UL;
// get GPS week and time
state.time_week = ret / (7*86400UL);
state.time_week_ms = (ret % (7*86400UL)) * 1000;
state.time_week_ms += msec;
}
/*
fill in 3D velocity for a GPS that doesn't give vertical velocity numbers
*/
void AP_GPS_Backend::fill_3d_velocity(void)
{
float gps_heading = ToRad(state.ground_course_cd * 0.01f);
state.velocity.x = state.ground_speed * cosf(gps_heading);
state.velocity.y = state.ground_speed * sinf(gps_heading);
state.velocity.z = 0;
state.have_vertical_velocity = false;
}