AP_GPS: add proxy driver for GNSS modules handled by PX4 firmware

libraries/AP_GPS/AP_GPS_PX4.cpp

+// -*- 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/>.
+ */
+
+//  GPS proxy driver for APM on PX4 platforms
+//
+//  This driver subscribes on PX4s vehicle_gps_position topic and presents the data received to APM.
+//  The publisher could be an UAVCAN GNSS module like http://docs.zubax.com/Zubax_GNSS, or any other GNSS
+//  hardware supported by the PX4 ecosystem.
+//
+//  Code by Holger Steinhaus
+
+#include "AP_GPS_PX4.h"
+#include <uORB/uORB.h>
+
+#include <math.h>
+
+extern const AP_HAL::HAL& hal;
+
+AP_GPS_PX4::AP_GPS_PX4(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port) :
+    AP_GPS_Backend(_gps, _state, _port)
+{
+    _gps_sub = orb_subscribe(ORB_ID(vehicle_gps_position));
+}
+
+
+#define MS_PER_WEEK             7*24*3600*1000LL
+#define DELTA_POSIX_GPS_EPOCH   315964800LL*1000LL
+#define LEAP_MS_GPS_2014        16*1000LL
+
+// update internal state if new GPS information is available
+bool
+AP_GPS_PX4::read(void)
+{
+    bool updated = false;
+    orb_check(_gps_sub, &updated);
+
+    if (updated) {
+        if (OK == orb_copy(ORB_ID(vehicle_gps_position), _gps_sub, &_gps_pos)) {
+            state.last_gps_time_ms = hal.scheduler->millis();
+            state.status  = (AP_GPS::GPS_Status) (_gps_pos.fix_type | AP_GPS::NO_FIX);
+            state.num_sats = _gps_pos.satellites_used;
+            state.hdop = uint16_t(_gps_pos.eph*100.0f + .5f);
+
+            state.location.lat = _gps_pos.lat;
+            state.location.lng = _gps_pos.lon;
+            state.location.alt = _gps_pos.alt/10;
+
+            state.ground_speed = _gps_pos.vel_m_s;
+            state.ground_course_cd = int32_t(double(_gps_pos.cog_rad) / M_PI * 18000. +.5);
+            state.have_vertical_velocity = _gps_pos.vel_ned_valid;
+            state.velocity.x = _gps_pos.vel_n_m_s;
+            state.velocity.y = _gps_pos.vel_e_m_s;
+            state.velocity.z = _gps_pos.vel_d_m_s;
+
+            // convert epoch timestamp back to gps epoch - evil hack until we get the genuine
+            // raw week information (or APM switches to Posix epoch ;-) )
+            uint64_t epoch_ms = uint64_t(_gps_pos.time_gps_usec/1000.+.5);
+            uint64_t gps_ms = epoch_ms - DELTA_POSIX_GPS_EPOCH + LEAP_MS_GPS_2014;
+            state.time_week = uint16_t(gps_ms / uint64_t(MS_PER_WEEK));
+            state.time_week_ms = uint32_t(gps_ms - uint64_t(state.time_week)*MS_PER_WEEK);
+        }
+    }
+
+    return updated;
+}
\ No newline at end of file

libraries/AP_GPS/AP_GPS_PX4.h

+// -*- 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/>.
+ */
+
+//
+//  GPS proxy driver for APM on PX4 platforms
+//  Code by Holger Steinhaus
+//
+#ifndef __AP_GPS_PX4_H__
+#define __AP_GPS_PX4_H__
+
+#include <AP_HAL.h>
+#include <AP_GPS.h>
+#include <modules/uORB/topics/vehicle_gps_position.h>
+
+class AP_GPS_PX4 : public AP_GPS_Backend {
+public:
+    AP_GPS_PX4(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);
+
+    bool read();
+
+private:
+    int                           _gps_sub;
+    struct vehicle_gps_position_s _gps_pos;
+};
+
+#endif // AP_GPS_SIRF_h