void
MulticopterAttitudeControl::task_main()
{
	warnx("started");
	fflush(stdout);

	/*
	 * do subscriptions
	 */
	_v_att_sp_sub = orb_subscribe(ORB_ID(vehicle_attitude_setpoint));
	_v_rates_sp_sub = orb_subscribe(ORB_ID(vehicle_rates_setpoint));
	_v_att_sub = orb_subscribe(ORB_ID(vehicle_attitude));
	_v_control_mode_sub = orb_subscribe(ORB_ID(vehicle_control_mode));
	_params_sub = orb_subscribe(ORB_ID(parameter_update));
	_manual_control_sp_sub = orb_subscribe(ORB_ID(manual_control_setpoint));
	_armed_sub = orb_subscribe(ORB_ID(actuator_armed));

	/* initialize parameters cache */
	parameters_update();

	/* wakeup source: vehicle attitude */
	struct pollfd fds[1];

	fds[0].fd = _v_att_sub;
	fds[0].events = POLLIN;

	while (!_task_should_exit) {

		/* wait for up to 100ms for data */
		int pret = poll(&fds[0], (sizeof(fds) / sizeof(fds[0])), 100);

		/* timed out - periodic check for _task_should_exit */
		if (pret == 0)
			continue;

		/* this is undesirable but not much we can do - might want to flag unhappy status */
		if (pret < 0) {
			warn("poll error %d, %d", pret, errno);
			/* sleep a bit before next try */
			usleep(100000);
			continue;
		}

		perf_begin(_loop_perf);

		/* run controller on attitude changes */
		if (fds[0].revents & POLLIN) {
			static uint64_t last_run = 0;
			float dt = (hrt_absolute_time() - last_run) / 1000000.0f;
			last_run = hrt_absolute_time();

			/* guard against too small (< 2ms) and too large (> 20ms) dt's */
			if (dt < 0.002f) {
				dt = 0.002f;

			} else if (dt > 0.02f) {
				dt = 0.02f;
			}

			/* copy attitude topic */
			orb_copy(ORB_ID(vehicle_attitude), _v_att_sub, &_v_att);

			/* check for updates in other topics */
			parameter_update_poll();
			vehicle_control_mode_poll();
			arming_status_poll();
			vehicle_manual_poll();

			if (_v_control_mode.flag_control_attitude_enabled) {
				control_attitude(dt);

				/* publish attitude rates setpoint */
				_v_rates_sp.roll = _rates_sp(0);
				_v_rates_sp.pitch = _rates_sp(1);
				_v_rates_sp.yaw = _rates_sp(2);
				_v_rates_sp.thrust = _thrust_sp;
				_v_rates_sp.timestamp = hrt_absolute_time();

				if (_v_rates_sp_pub > 0) {
					orb_publish(ORB_ID(vehicle_rates_setpoint), _v_rates_sp_pub, &_v_rates_sp);

				} else {
					_v_rates_sp_pub = orb_advertise(ORB_ID(vehicle_rates_setpoint), &_v_rates_sp);
				}

			} else {
				/* attitude controller disabled, poll rates setpoint topic */
				vehicle_rates_setpoint_poll();
				_rates_sp(0) = _v_rates_sp.roll;
				_rates_sp(1) = _v_rates_sp.pitch;
				_rates_sp(2) = _v_rates_sp.yaw;
				_thrust_sp = _v_rates_sp.thrust;
			}

			if (_v_control_mode.flag_control_rates_enabled) {
				control_attitude_rates(dt);

				/* publish actuator controls */
				_actuators.control[0] = (isfinite(_att_control(0))) ? _att_control(0) : 0.0f;
				_actuators.control[1] = (isfinite(_att_control(1))) ? _att_control(1) : 0.0f;
				_actuators.control[2] = (isfinite(_att_control(2))) ? _att_control(2) : 0.0f;
				_actuators.control[3] = (isfinite(_thrust_sp)) ? _thrust_sp : 0.0f;
				_actuators.timestamp = hrt_absolute_time();

				if (_actuators_0_pub > 0) {
					orb_publish(ORB_ID(actuator_controls_0), _actuators_0_pub, &_actuators);

				} else {
					_actuators_0_pub = orb_advertise(ORB_ID(actuator_controls_0), &_actuators);
				}
			}
		}

		perf_end(_loop_perf);
	}

	warnx("exit");

	_control_task = -1;
	_exit(0);
}
void
MulticopterAttitudeControl::task_main()
{

	/*
	 * do subscriptions
	 */
	_v_att_sp_sub = orb_subscribe(ORB_ID(vehicle_attitude_setpoint));
	_v_rates_sp_sub = orb_subscribe(ORB_ID(vehicle_rates_setpoint));
	_ctrl_state_sub = orb_subscribe(ORB_ID(control_state));
	_v_control_mode_sub = orb_subscribe(ORB_ID(vehicle_control_mode));
	_params_sub = orb_subscribe(ORB_ID(parameter_update));
	_manual_control_sp_sub = orb_subscribe(ORB_ID(manual_control_setpoint));
	_armed_sub = orb_subscribe(ORB_ID(actuator_armed));
	_vehicle_status_sub = orb_subscribe(ORB_ID(vehicle_status));
	_motor_limits_sub = orb_subscribe(ORB_ID(multirotor_motor_limits));

	/* initialize parameters cache */
	parameters_update();

	/* wakeup source: vehicle attitude */
	px4_pollfd_struct_t fds[1];

	fds[0].fd = _ctrl_state_sub;
	fds[0].events = POLLIN;

	while (!_task_should_exit) {

		/* wait for up to 100ms for data */
		int pret = px4_poll(&fds[0], (sizeof(fds) / sizeof(fds[0])), 100);

		/* timed out - periodic check for _task_should_exit */
		if (pret == 0) {
			continue;
		}

		/* this is undesirable but not much we can do - might want to flag unhappy status */
		if (pret < 0) {
			warn("poll error %d, %d", pret, errno);
			/* sleep a bit before next try */
			usleep(100000);
			continue;
		}

		perf_begin(_loop_perf);

		/* run controller on attitude changes */
		if (fds[0].revents & POLLIN) {
			static uint64_t last_run = 0;
			float dt = (hrt_absolute_time() - last_run) / 1000000.0f;
			last_run = hrt_absolute_time();

			/* guard against too small (< 2ms) and too large (> 20ms) dt's */
			if (dt < 0.002f) {
				dt = 0.002f;

			} else if (dt > 0.02f) {
				dt = 0.02f;
			}

			/* copy attitude and control state topics */
			orb_copy(ORB_ID(control_state), _ctrl_state_sub, &_ctrl_state);

			/* check for updates in other topics */
			parameter_update_poll();
			vehicle_control_mode_poll();
			arming_status_poll();
			vehicle_manual_poll();
			vehicle_status_poll();
			vehicle_motor_limits_poll();

			/* Check if we are in rattitude mode and the pilot is above the threshold on pitch
			 * or roll (yaw can rotate 360 in normal att control).  If both are true don't
			 * even bother running the attitude controllers */
			if (_vehicle_status.main_state == vehicle_status_s::MAIN_STATE_RATTITUDE) {
				if (fabsf(_manual_control_sp.y) > _params.rattitude_thres ||
				    fabsf(_manual_control_sp.x) > _params.rattitude_thres) {
					_v_control_mode.flag_control_attitude_enabled = false;
				}
			}

			if (_v_control_mode.flag_control_attitude_enabled) {

				if (_ts_opt_recovery == nullptr) {
					// the  tailsitter recovery instance has not been created, thus, the vehicle
					// is not a tailsitter, do normal attitude control
					control_attitude(dt);

				} else {
					vehicle_attitude_setpoint_poll();
					_thrust_sp = _v_att_sp.thrust;
					math::Quaternion q(_ctrl_state.q[0], _ctrl_state.q[1], _ctrl_state.q[2], _ctrl_state.q[3]);
					math::Quaternion q_sp(&_v_att_sp.q_d[0]);
					_ts_opt_recovery->setAttGains(_params.att_p, _params.yaw_ff);
					_ts_opt_recovery->calcOptimalRates(q, q_sp, _v_att_sp.yaw_sp_move_rate, _rates_sp);

					/* limit rates */
					for (int i = 0; i < 3; i++) {
						_rates_sp(i) = math::constrain(_rates_sp(i), -_params.mc_rate_max(i), _params.mc_rate_max(i));
					}
				}

				/* publish attitude rates setpoint */
				_v_rates_sp.roll = _rates_sp(0);
				_v_rates_sp.pitch = _rates_sp(1);
				_v_rates_sp.yaw = _rates_sp(2);
				_v_rates_sp.thrust = _thrust_sp;
				_v_rates_sp.timestamp = hrt_absolute_time();

				if (_v_rates_sp_pub != nullptr) {
					orb_publish(_rates_sp_id, _v_rates_sp_pub, &_v_rates_sp);

				} else if (_rates_sp_id) {
					_v_rates_sp_pub = orb_advertise(_rates_sp_id, &_v_rates_sp);
				}

				//}

			} else {
				/* attitude controller disabled, poll rates setpoint topic */
				if (_v_control_mode.flag_control_manual_enabled) {
					/* manual rates control - ACRO mode */
					_rates_sp = math::Vector<3>(_manual_control_sp.y, -_manual_control_sp.x,
								    _manual_control_sp.r).emult(_params.acro_rate_max);
					_thrust_sp = math::min(_manual_control_sp.z, MANUAL_THROTTLE_MAX_MULTICOPTER);

					/* publish attitude rates setpoint */
					_v_rates_sp.roll = _rates_sp(0);
					_v_rates_sp.pitch = _rates_sp(1);
					_v_rates_sp.yaw = _rates_sp(2);
					_v_rates_sp.thrust = _thrust_sp;
					_v_rates_sp.timestamp = hrt_absolute_time();

					if (_v_rates_sp_pub != nullptr) {
						orb_publish(_rates_sp_id, _v_rates_sp_pub, &_v_rates_sp);

					} else if (_rates_sp_id) {
						_v_rates_sp_pub = orb_advertise(_rates_sp_id, &_v_rates_sp);
					}

				} else {
					/* attitude controller disabled, poll rates setpoint topic */
					vehicle_rates_setpoint_poll();
					_rates_sp(0) = _v_rates_sp.roll;
					_rates_sp(1) = _v_rates_sp.pitch;
					_rates_sp(2) = _v_rates_sp.yaw;
					_thrust_sp = _v_rates_sp.thrust;
				}
			}

			if (_v_control_mode.flag_control_rates_enabled) {
				control_attitude_rates(dt);

				/* publish actuator controls */
				_actuators.control[0] = (PX4_ISFINITE(_att_control(0))) ? _att_control(0) : 0.0f;
				_actuators.control[1] = (PX4_ISFINITE(_att_control(1))) ? _att_control(1) : 0.0f;
				_actuators.control[2] = (PX4_ISFINITE(_att_control(2))) ? _att_control(2) : 0.0f;
				_actuators.control[3] = (PX4_ISFINITE(_thrust_sp)) ? _thrust_sp : 0.0f;
				_actuators.timestamp = hrt_absolute_time();
				_actuators.timestamp_sample = _ctrl_state.timestamp;

				_controller_status.roll_rate_integ = _rates_int(0);
				_controller_status.pitch_rate_integ = _rates_int(1);
				_controller_status.yaw_rate_integ = _rates_int(2);
				_controller_status.timestamp = hrt_absolute_time();

				if (!_actuators_0_circuit_breaker_enabled) {
					if (_actuators_0_pub != nullptr) {
						orb_publish(_actuators_id, _actuators_0_pub, &_actuators);
						perf_end(_controller_latency_perf);

					} else if (_actuators_id) {
						_actuators_0_pub = orb_advertise(_actuators_id, &_actuators);
					}

				}

				/* publish controller status */
				if (_controller_status_pub != nullptr) {
					orb_publish(ORB_ID(mc_att_ctrl_status), _controller_status_pub, &_controller_status);

				} else {
					_controller_status_pub = orb_advertise(ORB_ID(mc_att_ctrl_status), &_controller_status);
				}
			}
		}

		perf_end(_loop_perf);
	}

	_control_task = -1;
	return;
}
int ardrone_control_main(int argc, char *argv[])
{
	/* welcome user */
	printf("[ardrone_control] Control started, taking over motors\n");

	/* default values for arguments */
	char *ardrone_uart_name = "/dev/ttyS1";
	control_mode = CONTROL_MODE_RATES;

	char *commandline_usage = "\tusage: ardrone_control -d ardrone-devicename -m mode\n\tmodes are:\n\t\trates\n\t\tattitude\n";

	/* read commandline arguments */
	int i;

	for (i = 1; i < argc; i++) {
		if (strcmp(argv[i], "-d") == 0 || strcmp(argv[i], "--device") == 0) { //ardrone set
			if (argc > i + 1) {
				ardrone_uart_name = argv[i + 1];

			} else {
				printf(commandline_usage);
				return 0;
			}

		} else if (strcmp(argv[i], "-m") == 0 || strcmp(argv[i], "--mode") == 0) {
			if (argc > i + 1) {
				if (strcmp(argv[i + 1], "rates") == 0) {
					control_mode = CONTROL_MODE_RATES;

				} else if (strcmp(argv[i + 1], "attitude") == 0) {
					control_mode = CONTROL_MODE_ATTITUDE;

				} else {
					printf(commandline_usage);
					return 0;
				}

			} else {
				printf(commandline_usage);
				return 0;
			}
		}
	}

	/* open uarts */
	printf("[ardrone_control] AR.Drone UART is %s\n", ardrone_uart_name);
	ardrone_write = open(ardrone_uart_name, O_RDWR | O_NOCTTY | O_NDELAY);

	/* initialize motors */
	ar_init_motors(ardrone_write, &gpios);
	int counter = 0;

	/* pthread for position control */
	pthread_t position_control_thread;
	position_control_thread_started = false;

	/* structures */
	struct vehicle_status_s state;
	struct vehicle_attitude_s att;
	struct ardrone_control_s ar_control;
	struct rc_channels_s rc;
	struct sensor_combined_s raw;
	struct ardrone_motors_setpoint_s setpoint;

	/* subscribe to attitude, motor setpoints and system state */
	int att_sub = orb_subscribe(ORB_ID(vehicle_attitude));
	int state_sub = orb_subscribe(ORB_ID(vehicle_status));
	int rc_sub = orb_subscribe(ORB_ID(rc_channels));
	int sensor_sub = orb_subscribe(ORB_ID(sensor_combined));
	int setpoint_sub = orb_subscribe(ORB_ID(ardrone_motors_setpoint));

	/* publish AR.Drone motor control state */
	int ardrone_pub = orb_advertise(ORB_ID(ardrone_control), &ar_control);

	while (1) {
		/* get a local copy of the vehicle state */
		orb_copy(ORB_ID(vehicle_status), state_sub, &state);
		/* get a local copy of rc */
		orb_copy(ORB_ID(rc_channels), rc_sub, &rc);
		/* get a local copy of attitude */
		orb_copy(ORB_ID(vehicle_attitude), att_sub, &att);

		if (state.state_machine == SYSTEM_STATE_AUTO) {
			if (false == position_control_thread_started) {
				pthread_attr_t position_control_thread_attr;
				pthread_attr_init(&position_control_thread_attr);
				pthread_attr_setstacksize(&position_control_thread_attr, 2048);
				pthread_create(&position_control_thread, &position_control_thread_attr, position_control_loop, &state);
				position_control_thread_started = true;
			}

			control_attitude(&rc, &att, &state, ardrone_pub, &ar_control);

			//No check for remote sticks to disarm in auto mode, land/disarm with ground station

		} else if (state.state_machine == SYSTEM_STATE_MANUAL) {
			if (control_mode == CONTROL_MODE_RATES) {
				orb_copy(ORB_ID(sensor_combined), sensor_sub, &raw);
				orb_copy(ORB_ID(ardrone_motors_setpoint), setpoint_sub, &setpoint);
				control_rates(&raw, &setpoint);

			} else if (control_mode == CONTROL_MODE_ATTITUDE) {
				control_attitude(&rc, &att, &state, ardrone_pub, &ar_control);
			}

		} else {

		}

		//fancy led animation...
		static int blubb = 0;

		if (counter % 20 == 0) {
			if (blubb == 0) ar_set_leds(ardrone_write, 0, 1, 0, 0, 0, 0, 0 , 0);

			if (blubb == 1) ar_set_leds(ardrone_write, 1, 1, 0, 0, 0, 0, 0 , 0);

			if (blubb == 2) ar_set_leds(ardrone_write, 1, 0, 0, 0, 0, 0, 0 , 0);

			if (blubb == 3) ar_set_leds(ardrone_write, 0, 0, 0, 1, 0, 0, 0 , 0);

			if (blubb == 4) ar_set_leds(ardrone_write, 0, 0, 1, 1, 0, 0, 0 , 0);

			if (blubb == 5) ar_set_leds(ardrone_write, 0, 0, 1, 0, 0, 0, 0 , 0);

			if (blubb == 6) ar_set_leds(ardrone_write, 0, 0, 0, 0, 0, 1, 0 , 0);

			if (blubb == 7) ar_set_leds(ardrone_write, 0, 0, 0, 0, 1, 1, 0 , 0);

			if (blubb == 8) ar_set_leds(ardrone_write, 0, 0, 0, 0, 1, 0, 0 , 0);

			if (blubb == 9) ar_set_leds(ardrone_write, 0, 0, 0, 0, 0, 0, 0 , 1);

			if (blubb == 10) ar_set_leds(ardrone_write, 0, 0, 0, 0, 0, 0, 1 , 1);

			if (blubb == 11) ar_set_leds(ardrone_write, 0, 0, 0, 0, 0, 0, 1 , 0);

			blubb++;

			if (blubb == 12) blubb = 0;
		}

		/* run at approximately 200 Hz */
		usleep(5000);
		counter++;
	}

	/* close uarts */
	close(ardrone_write);
	ar_multiplexing_deinit(gpios);

	printf("[ardrone_control] ending now...\r\n");
	fflush(stdout);
	return 0;
}
void
MulticopterAttitudeControl::task_main()
{

	/*
	 * do subscriptions
	 */
	_v_att_sp_sub = orb_subscribe(ORB_ID(vehicle_attitude_setpoint));
	_v_rates_sp_sub = orb_subscribe(ORB_ID(vehicle_rates_setpoint));
	_v_att_sub = orb_subscribe(ORB_ID(vehicle_attitude));
	_v_control_mode_sub = orb_subscribe(ORB_ID(vehicle_control_mode));
	_params_sub = orb_subscribe(ORB_ID(parameter_update));
	_manual_control_sp_sub = orb_subscribe(ORB_ID(manual_control_setpoint));
	_armed_sub = orb_subscribe(ORB_ID(actuator_armed));
	_vehicle_status_sub = orb_subscribe(ORB_ID(vehicle_status));
	_motor_limits_sub = orb_subscribe(ORB_ID(multirotor_motor_limits));

	/* initialize parameters cache */
	parameters_update();

	/* wakeup source: vehicle attitude */
	px4_pollfd_struct_t fds[1];

	fds[0].fd = _v_att_sub;
	fds[0].events = POLLIN;

	while (!_task_should_exit) {

		/* wait for up to 100ms for data */
		int pret = px4_poll(&fds[0], (sizeof(fds) / sizeof(fds[0])), 100);

		/* timed out - periodic check for _task_should_exit */
		if (pret == 0)
			continue;

		/* this is undesirable but not much we can do - might want to flag unhappy status */
		if (pret < 0) {
			warn("poll error %d, %d", pret, errno);
			/* sleep a bit before next try */
			usleep(100000);
			continue;
		}

		perf_begin(_loop_perf);

		/* run controller on attitude changes */
		if (fds[0].revents & POLLIN) {
			static uint64_t last_run = 0;
			float dt = (hrt_absolute_time() - last_run) / 1000000.0f;
			last_run = hrt_absolute_time();

			/* guard against too small (< 2ms) and too large (> 20ms) dt's */
			if (dt < 0.002f) {
				dt = 0.002f;

			} else if (dt > 0.02f) {
				dt = 0.02f;
			}

			/* copy attitude topic */
			orb_copy(ORB_ID(vehicle_attitude), _v_att_sub, &_v_att);

			/* check for updates in other topics */
			parameter_update_poll();
			vehicle_control_mode_poll();
			arming_status_poll();
			vehicle_manual_poll();
			vehicle_status_poll();
			vehicle_motor_limits_poll();

			if (_v_control_mode.flag_control_attitude_enabled) {
				control_attitude(dt);

				/* publish attitude rates setpoint */
				_v_rates_sp.roll = _rates_sp(0);
				_v_rates_sp.pitch = _rates_sp(1);
				_v_rates_sp.yaw = _rates_sp(2);
				_v_rates_sp.thrust = _thrust_sp;
				_v_rates_sp.timestamp = hrt_absolute_time();

				if (_v_rates_sp_pub != nullptr) {
					orb_publish(_rates_sp_id, _v_rates_sp_pub, &_v_rates_sp);

				} else if (_rates_sp_id) {
					_v_rates_sp_pub = orb_advertise(_rates_sp_id, &_v_rates_sp);
				}

			} else {
				/* attitude controller disabled, poll rates setpoint topic */
				if (_v_control_mode.flag_control_manual_enabled) {
					/* manual rates control - ACRO mode */
					_rates_sp = math::Vector<3>(_manual_control_sp.y, -_manual_control_sp.x, _manual_control_sp.r).emult(_params.acro_rate_max);
					_thrust_sp = _manual_control_sp.z;

					/* publish attitude rates setpoint */
					_v_rates_sp.roll = _rates_sp(0);
					_v_rates_sp.pitch = _rates_sp(1);
					_v_rates_sp.yaw = _rates_sp(2);
					_v_rates_sp.thrust = _thrust_sp;
					_v_rates_sp.timestamp = hrt_absolute_time();

					if (_v_rates_sp_pub != nullptr) {
						orb_publish(_rates_sp_id, _v_rates_sp_pub, &_v_rates_sp);

					} else if (_rates_sp_id) {
						_v_rates_sp_pub = orb_advertise(_rates_sp_id, &_v_rates_sp);
					}

				} else {
					/* attitude controller disabled, poll rates setpoint topic */
					vehicle_rates_setpoint_poll();
					_rates_sp(0) = _v_rates_sp.roll;
					_rates_sp(1) = _v_rates_sp.pitch;
					_rates_sp(2) = _v_rates_sp.yaw;
					_thrust_sp = _v_rates_sp.thrust;
				}
			}

			if (_v_control_mode.flag_control_rates_enabled) {
				control_attitude_rates(dt);

				/* publish actuator controls */
				_actuators.control[0] = (PX4_ISFINITE(_att_control(0))) ? _att_control(0) : 0.0f;
				_actuators.control[1] = (PX4_ISFINITE(_att_control(1))) ? _att_control(1) : 0.0f;
				_actuators.control[2] = (PX4_ISFINITE(_att_control(2))) ? _att_control(2) : 0.0f;
				_actuators.control[3] = (PX4_ISFINITE(_thrust_sp)) ? _thrust_sp : 0.0f;
				_actuators.timestamp = hrt_absolute_time();
				_actuators.timestamp_sample = _v_att.timestamp;

				_controller_status.roll_rate_integ = _rates_int(0);
				_controller_status.pitch_rate_integ = _rates_int(1);
				_controller_status.yaw_rate_integ = _rates_int(2);
				_controller_status.timestamp = hrt_absolute_time();

				if (!_actuators_0_circuit_breaker_enabled) {
					if (_actuators_0_pub != nullptr) {
						orb_publish(_actuators_id, _actuators_0_pub, &_actuators);
						perf_end(_controller_latency_perf);

					} else if (_actuators_id) {
						_actuators_0_pub = orb_advertise(_actuators_id, &_actuators);
					}

				}

				/* publish controller status */
				if(_controller_status_pub != nullptr) {
					orb_publish(ORB_ID(mc_att_ctrl_status),_controller_status_pub, &_controller_status);
				} else {
					_controller_status_pub = orb_advertise(ORB_ID(mc_att_ctrl_status), &_controller_status);
				}
			}
		}

		perf_end(_loop_perf);
	}

	_control_task = -1;
	return;
}
Exemple #5
0
/* Main Thread */
int rover_steering_control_thread_main(int argc, char *argv[])
{
	/* read arguments */
	bool verbose = false;

	for (int i = 1; i < argc; i++) {
		if (strcmp(argv[i], "-v") == 0 || strcmp(argv[i], "--verbose") == 0) {
			verbose = true;
		}
	}

	/* initialize parameters, first the handles, then the values */
	parameters_init(&ph);
	parameters_update(&ph, &pp);


	/*
	 * PX4 uses a publish/subscribe design pattern to enable
	 * multi-threaded communication.
	 *
	 * The most elegant aspect of this is that controllers and
	 * other processes can either 'react' to new data, or run
	 * at their own pace.
	 *
	 * PX4 developer guide:
	 * https://pixhawk.ethz.ch/px4/dev/shared_object_communication
	 *
	 * Wikipedia description:
	 * http://en.wikipedia.org/wiki/Publish–subscribe_pattern
	 *
	 */




	/*
	 * Declare and safely initialize all structs to zero.
	 *
	 * These structs contain the system state and things
	 * like attitude, position, the current waypoint, etc.
	 */
	struct vehicle_attitude_s att;
	memset(&att, 0, sizeof(att));
	struct vehicle_attitude_setpoint_s att_sp;
	memset(&att_sp, 0, sizeof(att_sp));
	struct vehicle_global_position_s global_pos;
	memset(&global_pos, 0, sizeof(global_pos));
	struct manual_control_setpoint_s manual_sp;
	memset(&manual_sp, 0, sizeof(manual_sp));
	struct vehicle_status_s vstatus;
	memset(&vstatus, 0, sizeof(vstatus));
	struct position_setpoint_s global_sp;
	memset(&global_sp, 0, sizeof(global_sp));

	/* output structs - this is what is sent to the mixer */
	struct actuator_controls_s actuators;
	memset(&actuators, 0, sizeof(actuators));


	/* publish actuator controls with zero values */
	for (unsigned i = 0; i < (sizeof(actuators.control) / sizeof(actuators.control[0])); i++) {
		actuators.control[i] = 0.0f;
	}

	struct vehicle_attitude_setpoint_s _att_sp = {};

	/*
	 * Advertise that this controller will publish actuator
	 * control values and the rate setpoint
	 */
	orb_advert_t actuator_pub = orb_advertise(ORB_ID_VEHICLE_ATTITUDE_CONTROLS, &actuators);

	/* subscribe to topics. */
	int att_sub = orb_subscribe(ORB_ID(vehicle_attitude));

	int global_pos_sub = orb_subscribe(ORB_ID(vehicle_global_position));

	int manual_sp_sub = orb_subscribe(ORB_ID(manual_control_setpoint));

	int vstatus_sub = orb_subscribe(ORB_ID(vehicle_status));

	int att_sp_sub = orb_subscribe(ORB_ID(vehicle_attitude_setpoint));

	int param_sub = orb_subscribe(ORB_ID(parameter_update));

	/* Setup of loop */

	struct pollfd fds[2];

	fds[0].fd = param_sub;

	fds[0].events = POLLIN;

	fds[1].fd = att_sub;

	fds[1].events = POLLIN;

	while (!thread_should_exit) {

		/*
		 * Wait for a sensor or param update, check for exit condition every 500 ms.
		 * This means that the execution will block here without consuming any resources,
		 * but will continue to execute the very moment a new attitude measurement or
		 * a param update is published. So no latency in contrast to the polling
		 * design pattern (do not confuse the poll() system call with polling).
		 *
		 * This design pattern makes the controller also agnostic of the attitude
		 * update speed - it runs as fast as the attitude updates with minimal latency.
		 */
		int ret = poll(fds, 2, 500);

		if (ret < 0) {
			/*
			 * Poll error, this will not really happen in practice,
			 * but its good design practice to make output an error message.
			 */
			warnx("poll error");

		} else if (ret == 0) {
			/* no return value = nothing changed for 500 ms, ignore */
		} else {

			/* only update parameters if they changed */
			if (fds[0].revents & POLLIN) {
				/* read from param to clear updated flag (uORB API requirement) */
				struct parameter_update_s update;
				orb_copy(ORB_ID(parameter_update), param_sub, &update);

				/* if a param update occured, re-read our parameters */
				parameters_update(&ph, &pp);
			}

			/* only run controller if attitude changed */
			if (fds[1].revents & POLLIN) {


				/* Check if there is a new position measurement or position setpoint */
				bool pos_updated;
				orb_check(global_pos_sub, &pos_updated);
				bool att_sp_updated;
				orb_check(att_sp_sub, &att_sp_updated);
				bool manual_sp_updated;
				orb_check(manual_sp_sub, &manual_sp_updated);

				/* get a local copy of attitude */
				orb_copy(ORB_ID(vehicle_attitude), att_sub, &att);

				if (att_sp_updated) {
					orb_copy(ORB_ID(vehicle_attitude_setpoint), att_sp_sub, &_att_sp);
				}

				/* control attitude / heading */
				control_attitude(&_att_sp, &att, &actuators);

				if (manual_sp_updated)
					/* get the RC (or otherwise user based) input */
				{
					orb_copy(ORB_ID(manual_control_setpoint), manual_sp_sub, &manual_sp);
				}

				// XXX copy from manual depending on flight / usage mode to override

				/* get the system status and the flight mode we're in */
				orb_copy(ORB_ID(vehicle_status), vstatus_sub, &vstatus);

				/* sanity check and publish actuator outputs */
				if (isfinite(actuators.control[0]) &&
				    isfinite(actuators.control[1]) &&
				    isfinite(actuators.control[2]) &&
				    isfinite(actuators.control[3])) {
					orb_publish(ORB_ID_VEHICLE_ATTITUDE_CONTROLS, actuator_pub, &actuators);

					if (verbose) {
						warnx("published");
					}
				}
			}
		}
	}

	warnx("exiting, stopping all motors.");
	thread_running = false;

	/* kill all outputs */
	for (unsigned i = 0; i < (sizeof(actuators.control) / sizeof(actuators.control[0])); i++) {
		actuators.control[i] = 0.0f;
	}

	actuators.timestamp = hrt_absolute_time();

	orb_publish(ORB_ID_VEHICLE_ATTITUDE_CONTROLS, actuator_pub, &actuators);

	fflush(stdout);

	return 0;
}