text: /****************************************************************************
   *
   *   Copyright (c) 2013-2015 PX4 Development Team. All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   * 3. Neither the name PX4 nor the names of its contributors may be
   *    used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
   * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
   * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   *
   ****************************************************************************/
  
  /**
   * @file px4flow.cpp
   * @author Dominik Honegger
   * @author Ban Siesta <bansiesta@gmail.com>
   *
   * Driver for the PX4FLOW module connected via I2C.
   */
  
  #include <px4_config.h>
  #include <px4_defines.h>
  #include <px4_getopt.h>
  
  #include <drivers/device/i2c.h>
  
  #include <sys/types.h>
  #include <stdint.h>
  #include <stdlib.h>
  #include <stdbool.h>
  #include <semaphore.h>
  #include <string.h>
  #include <fcntl.h>
  #include <poll.h>
  #include <errno.h>
  #include <stdio.h>
  #include <math.h>
  #include <unistd.h>
  
  #include <nuttx/arch.h>
  #include <nuttx/wqueue.h>
  #include <nuttx/clock.h>
  
  #include <perf/perf_counter.h>
  #include <systemlib/err.h>
  #include <parameters/param.h>
  
  #include <conversion/rotation.h>
  
  #include <drivers/drv_hrt.h>
  #include <drivers/drv_range_finder.h>
  #include <drivers/device/ringbuffer.h>
  
  #include <uORB/uORB.h>
  #include <uORB/topics/optical_flow.h>
  #include <uORB/topics/distance_sensor.h>
  
  #include <board_config.h>
  
  #define PX4FLOW0_DEVICE_PATH	"/dev/px4flow0"
  
  /* Configuration Constants */
  #define I2C_FLOW_ADDRESS_DEFAULT    0x42	///< 7-bit address. 8-bit address is 0x84, range 0x42 - 0x49
  #define I2C_FLOW_ADDRESS_MIN        0x42	///< 7-bit address.
  #define I2C_FLOW_ADDRESS_MAX        0x49	///< 7-bit address.
  
  /* PX4FLOW Registers addresses */
  #define PX4FLOW_REG			0x16	///< Measure Register 22
  
  #define PX4FLOW_CONVERSION_INTERVAL_DEFAULT 100000	///< in microseconds! = 10Hz
  #define PX4FLOW_CONVERSION_INTERVAL_MIN      10000	///< in microseconds! = 100 Hz
  #define PX4FLOW_CONVERSION_INTERVAL_MAX    1000000	///< in microseconds! = 1 Hz
  
  #define PX4FLOW_I2C_MAX_BUS_SPEED	400000	///< 400 KHz maximum speed
  
  #define PX4FLOW_MAX_DISTANCE 5.0f
  #define PX4FLOW_MIN_DISTANCE 0.3f
  
  #ifndef CONFIG_SCHED_WORKQUEUE
  # error This requires CONFIG_SCHED_WORKQUEUE.
  #endif
  
  #include "i2c_frame.h"
  
  class PX4FLOW: public device::I2C
  {
  public:
  	PX4FLOW(int bus, int address = I2C_FLOW_ADDRESS_DEFAULT, enum Rotation rotation = (enum Rotation)0,
  		int conversion_interval = PX4FLOW_CONVERSION_INTERVAL_DEFAULT,
  		uint8_t sonar_rotation = distance_sensor_s::ROTATION_DOWNWARD_FACING);
  	virtual ~PX4FLOW();
  
  	virtual int 		init();
  
  	virtual ssize_t		read(struct file *filp, char *buffer, size_t buflen);
  	virtual int			ioctl(struct file *filp, int cmd, unsigned long arg);
  
  	/**
  	 * Diagnostics - print some basic information about the driver.
  	 */
  	void				print_info();
  
  protected:
  	virtual int			probe();
  
  private:
  
  	uint8_t _sonar_rotation;
  	work_s				_work;
  	ringbuffer::RingBuffer		*_reports;
  	bool				_sensor_ok;
  	int				_measure_ticks;
  	bool				_collect_phase;
  	int			_class_instance;
  	int			_orb_class_instance;
  	orb_advert_t		_px4flow_topic;
  	orb_advert_t		_distance_sensor_topic;
  
  	perf_counter_t		_sample_perf;
  	perf_counter_t		_comms_errors;
  
  	unsigned                 _conversion_interval;
  
  	enum Rotation       _sensor_rotation;
  	float 				_sensor_min_range;
  	float 				_sensor_max_range;
  	float 				_sensor_max_flow_rate;
  
  	i2c_frame _frame;
  	i2c_integral_frame _frame_integral;
  
  	/**
  	 * Test whether the device supported by the driver is present at a
  	 * specific address.
  	 *
  	 * @param address	The I2C bus address to probe.
  	 * @return		True if the device is present.
  	 */
  	int					probe_address(uint8_t address);
  
  	/**
  	 * Initialise the automatic measurement state machine and start it.
  	 *
  	 * @note This function is called at open and error time.  It might make sense
  	 *       to make it more aggressive about resetting the bus in case of errors.
  	 */
  	void				start();
  
  	/**
  	 * Stop the automatic measurement state machine.
  	 */
  	void				stop();
  
  	/**
  	 * Perform a poll cycle; collect from the previous measurement
  	 * and start a new one.
  	 */
  	void				cycle();
  	int					measure();
  	int					collect();
  	/**
  	 * Static trampoline from the workq context; because we don't have a
  	 * generic workq wrapper yet.
  	 *
  	 * @param arg		Instance pointer for the driver that is polling.
  	 */
  	static void			cycle_trampoline(void *arg);
  
  };
  
  /*
   * Driver 'main' command.
   */
  extern "C" __EXPORT int px4flow_main(int argc, char *argv[]);
  
  PX4FLOW::PX4FLOW(int bus, int address, enum Rotation rotation, int conversion_interval, uint8_t sonar_rotation) :
  	I2C("PX4FLOW", PX4FLOW0_DEVICE_PATH, bus, address, PX4FLOW_I2C_MAX_BUS_SPEED), /* 100-400 KHz */
  	_sonar_rotation(sonar_rotation),
  	_reports(nullptr),
  	_sensor_ok(false),
  	_measure_ticks(0),
  	_collect_phase(false),
  	_class_instance(-1),
  	_orb_class_instance(-1),
  	_px4flow_topic(nullptr),
  	_distance_sensor_topic(nullptr),
  	_sample_perf(perf_alloc(PC_ELAPSED, "px4f_read")),
  	_comms_errors(perf_alloc(PC_COUNT, "px4f_com_err")),
  	_conversion_interval(conversion_interval),
  	_sensor_rotation(rotation)
  {
  	// disable debug() calls
  	_debug_enabled = false;
  
  	// work_cancel in the dtor will explode if we don't do this...
  	memset(&_work, 0, sizeof(_work));
  }
  
  PX4FLOW::~PX4FLOW()
  {
  	/* make sure we are truly inactive */
  	stop();
  
  	/* free any existing reports */
  	if (_reports != nullptr) {
  		delete _reports;
  	}
  
  	perf_free(_sample_perf);
  	perf_free(_comms_errors);
  }
  
  int
  PX4FLOW::init()
  {
  	int ret = PX4_ERROR;
  
  	/* do I2C init (and probe) first */
  	if (I2C::init() != OK) {
  		return ret;
  	}
  
  	/* allocate basic report buffers */
  	_reports = new ringbuffer::RingBuffer(2, sizeof(optical_flow_s));
  
  	if (_reports == nullptr) {
  		return ret;
  	}
  
  	_class_instance = register_class_devname(RANGE_FINDER_BASE_DEVICE_PATH);
  
  	/* get a publish handle on the range finder topic */
  	struct distance_sensor_s ds_report = {};
  
  	if (_class_instance == CLASS_DEVICE_PRIMARY) {
  		_distance_sensor_topic = orb_advertise_multi(ORB_ID(distance_sensor), &ds_report,
  					 &_orb_class_instance, ORB_PRIO_HIGH);
  
  		if (_distance_sensor_topic == nullptr) {
  			PX4_ERR("failed to create distance_sensor object");
  		}
  
  	} else {
  		DEVICE_LOG("not primary range device, not advertising");
  	}
  
  	ret = OK;
  	/* sensor is ok, but we don't really know if it is within range */
  	_sensor_ok = true;
  
  	/* get yaw rotation from sensor frame to body frame */
  	param_t rot = param_find("SENS_FLOW_ROT");
  
  	if (rot != PARAM_INVALID) {
  		int32_t val = 6; // the recommended installation for the flow sensor is with the Y sensor axis forward
  		param_get(rot, &val);
  
  		_sensor_rotation = (enum Rotation)val;
  	}
  
  	/* get operational limits of the sensor */
  	param_t hmin = param_find("SENS_FLOW_MINHGT");
  
  	if (hmin != PARAM_INVALID) {
  		float val = 0.7;
  		param_get(hmin, &val);
  
  		_sensor_min_range = val;
  	}
  
  	param_t hmax = param_find("SENS_FLOW_MAXHGT");
  
  	if (hmax != PARAM_INVALID) {
  		float val = 3.0;
  		param_get(hmax, &val);
  
  		_sensor_max_range = val;
  	}
  
  	param_t ratemax = param_find("SENS_FLOW_MAXR");
  
  	if (ratemax != PARAM_INVALID) {
  		float val = 2.5;
  		param_get(ratemax, &val);
  
  		_sensor_max_flow_rate = val;
  	}
  
  	return ret;
  }
  
  int
  PX4FLOW::probe()
  {
  	uint8_t val[I2C_FRAME_SIZE];
  
  	// to be sure this is not a ll40ls Lidar (which can also be on
  	// 0x42) we check if a I2C_FRAME_SIZE byte transfer works from address
  	// 0. The ll40ls gives an error for that, whereas the flow
  	// happily returns some data
  	if (transfer(nullptr, 0, &val[0], 22) != OK) {
  		return -EIO;
  	}
  
  	// that worked, so start a measurement cycle
  	return measure();
  }
  
  int
  PX4FLOW::ioctl(struct file *filp, int cmd, unsigned long arg)
  {
  	switch (cmd) {
  
  	case SENSORIOCSPOLLRATE: {
  			switch (arg) {
  
  			/* zero would be bad */
  			case 0:
  				return -EINVAL;
  
  			/* set default polling rate */
  			case SENSOR_POLLRATE_DEFAULT: {
  					/* do we need to start internal polling? */
  					bool want_start = (_measure_ticks == 0);
  
  					/* set interval for next measurement to minimum legal value */
  					_measure_ticks = USEC2TICK(_conversion_interval);
  
  					/* if we need to start the poll state machine, do it */
  					if (want_start) {
  						start();
  					}
  
  					return OK;
  				}
  
  			/* adjust to a legal polling interval in Hz */
  			default: {
  					/* do we need to start internal polling? */
  					bool want_start = (_measure_ticks == 0);
  
  					/* convert hz to tick interval via microseconds */
  					unsigned ticks = USEC2TICK(1000000 / arg);
  
  					/* check against maximum rate */
  					if (ticks < USEC2TICK(_conversion_interval)) {
  						return -EINVAL;
  					}
  
  					/* update interval for next measurement */
  					_measure_ticks = ticks;
  
  					/* if we need to start the poll state machine, do it */
  					if (want_start) {
  						start();
  					}
  
  					return OK;
  				}
  			}
  		}
  
  	default:
  		/* give it to the superclass */
  		return I2C::ioctl(filp, cmd, arg);
  	}
  }
  
  ssize_t
  PX4FLOW::read(struct file *filp, char *buffer, size_t buflen)
  {
  	unsigned count = buflen / sizeof(struct optical_flow_s);
  	struct optical_flow_s *rbuf = reinterpret_cast<struct optical_flow_s *>(buffer);
  	int ret = 0;
  
  	/* buffer must be large enough */
  	if (count < 1) {
  		return -ENOSPC;
  	}
  
  	/* if automatic measurement is enabled */
  	if (_measure_ticks > 0) {
  
  		/*
  		 * While there is space in the caller's buffer, and reports, copy them.
  		 * Note that we may be pre-empted by the workq thread while we are doing this;
  		 * we are careful to avoid racing with them.
  		 */
  		while (count--) {
  			if (_reports->get(rbuf)) {
  				ret += sizeof(*rbuf);
  				rbuf++;
  			}
  		}
  
  		/* if there was no data, warn the caller */
  		return ret ? ret : -EAGAIN;
  	}
  
  	/* manual measurement - run one conversion */
  	do {
  		_reports->flush();
  
  		/* trigger a measurement */
  		if (OK != measure()) {
  			ret = -EIO;
  			break;
  		}
  
  		/* run the collection phase */
  		if (OK != collect()) {
  			ret = -EIO;
  			break;
  		}
  
  		/* state machine will have generated a report, copy it out */
  		if (_reports->get(rbuf)) {
  			ret = sizeof(*rbuf);
  		}
  
  	} while (0);
  
  	return ret;
  }
  
  int
  PX4FLOW::measure()
  {
  	int ret;
  
  	/*
  	 * Send the command to begin a measurement.
  	 */
  	uint8_t cmd = PX4FLOW_REG;
  	ret = transfer(&cmd, 1, nullptr, 0);
  
  	if (OK != ret) {
  		perf_count(_comms_errors);
  		DEVICE_DEBUG("i2c::transfer returned %d", ret);
  		return ret;
  	}
  
  	ret = OK;
  
  	return ret;
  }
  
  int
  PX4FLOW::collect()
  {
  	int ret = -EIO;
  
  	/* read from the sensor */
  	uint8_t val[I2C_FRAME_SIZE + I2C_INTEGRAL_FRAME_SIZE] = { };
  
  	perf_begin(_sample_perf);
  
  	if (PX4FLOW_REG == 0x00) {
  		ret = transfer(nullptr, 0, &val[0], I2C_FRAME_SIZE + I2C_INTEGRAL_FRAME_SIZE);
  	}
  
  	if (PX4FLOW_REG == 0x16) {
  		ret = transfer(nullptr, 0, &val[0], I2C_INTEGRAL_FRAME_SIZE);
  	}
  
  	if (ret < 0) {
  		DEVICE_DEBUG("error reading from sensor: %d", ret);
  		perf_count(_comms_errors);
  		perf_end(_sample_perf);
  		return ret;
  	}
  
  	if (PX4FLOW_REG == 0) {
  		memcpy(&_frame, val, I2C_FRAME_SIZE);
  		memcpy(&_frame_integral, &(val[I2C_FRAME_SIZE]), I2C_INTEGRAL_FRAME_SIZE);
  	}
  
  	if (PX4FLOW_REG == 0x16) {
  		memcpy(&_frame_integral, val, I2C_INTEGRAL_FRAME_SIZE);
  	}
  
  
  	struct optical_flow_s report;
  
  	report.timestamp = hrt_absolute_time();
  
  	report.pixel_flow_x_integral = static_cast<float>(_frame_integral.pixel_flow_x_integral) / 10000.0f;//convert to radians
  
  	report.pixel_flow_y_integral = static_cast<float>(_frame_integral.pixel_flow_y_integral) / 10000.0f;//convert to radians
  
  	report.frame_count_since_last_readout = _frame_integral.frame_count_since_last_readout;
  
  	report.ground_distance_m = static_cast<float>(_frame_integral.ground_distance) / 1000.0f;//convert to meters
  
  	report.quality = _frame_integral.qual; //0:bad ; 255 max quality
  
  	report.gyro_x_rate_integral = static_cast<float>(_frame_integral.gyro_x_rate_integral) / 10000.0f; //convert to radians
  
  	report.gyro_y_rate_integral = static_cast<float>(_frame_integral.gyro_y_rate_integral) / 10000.0f; //convert to radians
  
  	report.gyro_z_rate_integral = static_cast<float>(_frame_integral.gyro_z_rate_integral) / 10000.0f; //convert to radians
  
  	report.integration_timespan = _frame_integral.integration_timespan; //microseconds
  
  	report.time_since_last_sonar_update = _frame_integral.sonar_timestamp;//microseconds
  
  	report.gyro_temperature = _frame_integral.gyro_temperature;//Temperature * 100 in centi-degrees Celsius
  
  	report.sensor_id = 0;
  
  	report.max_flow_rate = _sensor_max_flow_rate;
  
  	report.min_ground_distance = _sensor_min_range;
  
  	report.max_ground_distance = _sensor_max_range;
  
  	/* rotate measurements in yaw from sensor frame to body frame according to parameter SENS_FLOW_ROT */
  	float zeroval = 0.0f;
  
  	rotate_3f(_sensor_rotation, report.pixel_flow_x_integral, report.pixel_flow_y_integral, zeroval);
  
  	rotate_3f(_sensor_rotation, report.gyro_x_rate_integral, report.gyro_y_rate_integral, report.gyro_z_rate_integral);
  
  	if (_px4flow_topic == nullptr) {
  		_px4flow_topic = orb_advertise(ORB_ID(optical_flow), &report);
  
  	} else {
  		/* publish it */
  		orb_publish(ORB_ID(optical_flow), _px4flow_topic, &report);
  	}
  
  	/* publish to the distance_sensor topic as well */
  	struct distance_sensor_s distance_report;
  	distance_report.timestamp = report.timestamp;
  	distance_report.min_distance = PX4FLOW_MIN_DISTANCE;
  	distance_report.max_distance = PX4FLOW_MAX_DISTANCE;
  	distance_report.current_distance = report.ground_distance_m;
  	distance_report.covariance = 0.0f;
  	distance_report.signal_quality = -1;
  	distance_report.type = distance_sensor_s::MAV_DISTANCE_SENSOR_ULTRASOUND;
  	/* TODO: the ID needs to be properly set */
  	distance_report.id = 0;
  	distance_report.orientation = _sonar_rotation;
  
  	orb_publish(ORB_ID(distance_sensor), _distance_sensor_topic, &distance_report);
  
  	/* post a report to the ring */
  	_reports->force(&report);
  
  	/* notify anyone waiting for data */
  	poll_notify(POLLIN);
  
  	ret = OK;
  
  	perf_end(_sample_perf);
  	return ret;
  }
  
  void
  PX4FLOW::start()
  {
  	/* reset the report ring and state machine */
  	_collect_phase = false;
  	_reports->flush();
  
  	/* schedule a cycle to start things */
  	work_queue(HPWORK, &_work, (worker_t)&PX4FLOW::cycle_trampoline, this, 1);
  }
  
  void
  PX4FLOW::stop()
  {
  	work_cancel(HPWORK, &_work);
  }
  
  void
  PX4FLOW::cycle_trampoline(void *arg)
  {
  	PX4FLOW *dev = (PX4FLOW *)arg;
  
  	dev->cycle();
  }
  
  void
  PX4FLOW::cycle()
  {
  	if (OK != measure()) {
  		DEVICE_DEBUG("measure error");
  	}
  
  	/* perform collection */
  	if (OK != collect()) {
  		DEVICE_DEBUG("collection error");
  		/* restart the measurement state machine */
  		start();
  		return;
  	}
  
  	work_queue(HPWORK, &_work, (worker_t)&PX4FLOW::cycle_trampoline, this,
  		   _measure_ticks);
  
  }
  
  void
  PX4FLOW::print_info()
  {
  	perf_print_counter(_sample_perf);
  	perf_print_counter(_comms_errors);
  	printf("poll interval:  %u ticks\n", _measure_ticks);
  	_reports->print_info("report queue");
  }
  
  /**
   * Local functions in support of the shell command.
   */
  namespace px4flow
  {
  
  PX4FLOW	*g_dev = nullptr;
  bool start_in_progress = false;
  
  const int START_RETRY_COUNT = 5;
  const int START_RETRY_TIMEOUT = 1000;
  
  int start(int argc, char *argv[]);
  void stop();
  void test();
  void reset();
  void info();
  void usage();
  
  /**
   * Start the driver.
   */
  int
  start(int argc, char *argv[])
  {
  	int fd;
  
  	/* entry check: */
  	if (start_in_progress) {
  		PX4_WARN("start already in progress");
  		return 1;
  	}
  
  	if (g_dev != nullptr) {
  		start_in_progress = false;
  		PX4_WARN("already started");
  		return 1;
  	}
  
  	/* parse command line options */
  	int address = I2C_FLOW_ADDRESS_DEFAULT;
  	int conversion_interval = PX4FLOW_CONVERSION_INTERVAL_DEFAULT;
  
  	/* don't exit from getopt loop to leave getopt global variables in consistent state,
  	 * set error flag instead */
  	bool err_flag = false;
  	int ch;
  	int myoptind = 1;
  	const char *myoptarg = nullptr;
  	uint8_t sonar_rotation = distance_sensor_s::ROTATION_DOWNWARD_FACING;
  
  	while ((ch = px4_getopt(argc, argv, "a:i:R:", &myoptind, &myoptarg)) != EOF) {
  		switch (ch) {
  		case 'a':
  			address = strtoul(myoptarg, nullptr, 16);
  
  			if (address < I2C_FLOW_ADDRESS_MIN || address > I2C_FLOW_ADDRESS_MAX) {
  				PX4_WARN("invalid i2c address '%s'", myoptarg);
  				err_flag = true;
  
  			}
  
  			break;
  
  		case 'i':
  			conversion_interval = strtoul(myoptarg, nullptr, 10);
  
  			if (conversion_interval < PX4FLOW_CONVERSION_INTERVAL_MIN || conversion_interval > PX4FLOW_CONVERSION_INTERVAL_MAX) {
  				PX4_WARN("invalid conversion interval '%s'", myoptarg);
  				err_flag = true;
  			}
  
  			break;
  
  		case 'R':
  			sonar_rotation = (uint8_t)atoi(myoptarg);
  			PX4_INFO("Setting sonar orientation to %d", (int)sonar_rotation);
  
  			break;
  
  		default:
  			err_flag = true;
  			break;
  		}
  	}
  
  	if (err_flag) {
  		usage();
  		return PX4_ERROR;
  	}
  
  	/* starting */
  	start_in_progress = true;
  	PX4_INFO("scanning I2C buses for device..");
  
  	int retry_nr = 0;
  
  	while (1) {
  		const int busses_to_try[] = {
  			PX4_I2C_BUS_EXPANSION,
  #ifdef PX4_I2C_BUS_ESC
  			PX4_I2C_BUS_ESC,
  #endif
  #ifdef PX4_I2C_BUS_ONBOARD
  			PX4_I2C_BUS_ONBOARD,
  #endif
  #ifdef PX4_I2C_BUS_EXPANSION1
  			PX4_I2C_BUS_EXPANSION1,
  #endif
  #ifdef PX4_I2C_BUS_EXPANSION2
  			PX4_I2C_BUS_EXPANSION2,
  #endif
  
  			-1
  		};
  
  		const int *cur_bus = busses_to_try;
  
  		while (*cur_bus != -1) {
  			/* create the driver */
  			/* PX4_WARN("trying bus %d", *cur_bus); */
  			g_dev = new PX4FLOW(*cur_bus, address, (enum Rotation)0, conversion_interval, sonar_rotation);
  
  			if (g_dev == nullptr) {
  				/* this is a fatal error */
  				break;
  			}
  
  			/* init the driver: */
  			if (OK == g_dev->init()) {
  				/* success! */
  				break;
  			}
  
  			/* destroy it again because it failed. */
  			delete g_dev;
  			g_dev = nullptr;
  
  			/* try next! */
  			cur_bus++;
  		}
  
  		/* check whether we found it: */
  		if (*cur_bus != -1) {
  
  			/* check for failure: */
  			if (g_dev == nullptr) {
  				break;
  			}
  
  			/* set the poll rate to default, starts automatic data collection */
  			fd = open(PX4FLOW0_DEVICE_PATH, O_RDONLY);
  
  			if (fd < 0) {
  				break;
  			}
  
  			if (ioctl(fd, SENSORIOCSPOLLRATE, SENSOR_POLLRATE_DEFAULT) < 0) {
  				break;
  			}
  
  			/* success! */
  			start_in_progress = false;
  			return 0;
  		}
  
  		if (retry_nr < START_RETRY_COUNT) {
  			/* lets not be too verbose */
  			// PX4_WARN("PX4FLOW not found on I2C busses. Retrying in %d ms. Giving up in %d retries.", START_RETRY_TIMEOUT, START_RETRY_COUNT - retry_nr);
  			usleep(START_RETRY_TIMEOUT * 1000);
  			retry_nr++;
  
  		} else {
  			break;
  		}
  	}
  
  	if (g_dev != nullptr) {
  		delete g_dev;
  		g_dev = nullptr;
  	}
  
  	start_in_progress = false;
  	return 1;
  }
  
  /**
   * Stop the driver
   */
  void
  stop()
  {
  	start_in_progress = false;
  
  	if (g_dev != nullptr) {
  		delete g_dev;
  		g_dev = nullptr;
  
  	} else {
  		errx(1, "driver not running");
  	}
  
  	exit(0);
  }
  
  /**
   * Perform some basic functional tests on the driver;
   * make sure we can collect data from the sensor in polled
   * and automatic modes.
   */
  void
  test()
  {
  	struct optical_flow_s report;
  	ssize_t sz;
  	int ret;
  
  	int fd = open(PX4FLOW0_DEVICE_PATH, O_RDONLY);
  
  	if (fd < 0) {
  		err(1, "%s open failed (try 'px4flow start' if the driver is not running", PX4FLOW0_DEVICE_PATH);
  	}
  
  
  	/* do a simple demand read */
  	sz = read(fd, &report, sizeof(report));
  
  	if (sz != sizeof(report)) {
  		PX4_WARN("immediate read failed");
  	}
  
  	print_message(report);
  
  	/* start the sensor polling at 10Hz */
  	if (OK != ioctl(fd, SENSORIOCSPOLLRATE, 10)) {
  		errx(1, "failed to set 10Hz poll rate");
  	}
  
  	/* read the sensor 5x and report each value */
  	for (unsigned i = 0; i < 10; i++) {
  		struct pollfd fds;
  
  		/* wait for data to be ready */
  		fds.fd = fd;
  		fds.events = POLLIN;
  		ret = poll(&fds, 1, 2000);
  
  		if (ret != 1) {
  			errx(1, "timed out waiting for sensor data");
  		}
  
  		/* now go get it */
  		sz = read(fd, &report, sizeof(report));
  
  		if (sz != sizeof(report)) {
  			err(1, "periodic read failed");
  		}
  
  		print_message(report);
  	}
  
  	errx(0, "PASS");
  }
  
  /**
   * Reset the driver.
   */
  void
  reset()
  {
  	int fd = open(PX4FLOW0_DEVICE_PATH, O_RDONLY);
  
  	if (fd < 0) {
  		err(1, "failed ");
  	}
  
  	if (ioctl(fd, SENSORIOCRESET, 0) < 0) {
  		err(1, "driver reset failed");
  	}
  
  	if (ioctl(fd, SENSORIOCSPOLLRATE, SENSOR_POLLRATE_DEFAULT) < 0) {
  		err(1, "driver poll restart failed");
  	}
  
  	exit(0);
  }
  
  /**
   * Print a little info about the driver.
   */
  void
  info()
  {
  	if (g_dev == nullptr) {
  		errx(1, "driver not running");
  	}
  
  	printf("state @ %p\n", g_dev);
  	g_dev->print_info();
  
  	exit(0);
  }
  
  void usage()
  {
  	PX4_INFO("usage: px4flow {start|test|reset|info'}");
  	PX4_INFO("    [-a i2c_address]");
  	PX4_INFO("    [-i i2c_interval]");
  }
  
  } // namespace
  
  int
  px4flow_main(int argc, char *argv[])
  {
  	if (argc < 2) {
  		px4flow::usage();
  		return 1;
  	}
  
  	/*
  	 * Start/load the driver.
  	 */
  	if (!strcmp(argv[1], "start")) {
  		return px4flow::start(argc, argv);
  	}
  
  	/*
  	 * Stop the driver
  	 */
  	if (!strcmp(argv[1], "stop")) {
  		px4flow::stop();
  	}
  
  	/*
  	 * Test the driver/device.
  	 */
  	if (!strcmp(argv[1], "test")) {
  		px4flow::test();
  	}
  
  	/*
  	 * Reset the driver.
  	 */
  	if (!strcmp(argv[1], "reset")) {
  		px4flow::reset();
  	}
  
  	/*
  	 * Print driver information.
  	 */
  	if (!strcmp(argv[1], "info") || !strcmp(argv[1], "status")) {
  		px4flow::info();
  	}
  
  	px4flow::usage();
  	return 1;
  }
  