path: root/apps/drivers/hmc5883/hmc5883.cpp

/****************************************************************************
 *
 *   Copyright (C) 2012 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
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 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
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 ****************************************************************************/

/**
 * @file hmc5883.cpp
 *
 * Driver for the HMC5883 magnetometer connected via I2C.
 */

#include <nuttx/config.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 <arch/board/up_hrt.h>

#include <systemlib/perf_counter.h>
#include <systemlib/err.h>

#include <drivers/drv_mag.h>

/*
 * HMC5883 internal constants and data structures.
 */

/* Max measurement rate is 160Hz */
#define HMC5883_CONVERSION_INTERVAL	(1000000 / 160)	/* microseconds */

#define ADDR_CONF_A			0x00
#define ADDR_CONF_B			0x01
#define ADDR_MODE			0x02
#define ADDR_DATA_OUT_X_MSB		0x03
#define ADDR_DATA_OUT_X_LSB		0x04
#define ADDR_DATA_OUT_Z_MSB		0x05
#define ADDR_DATA_OUT_Z_LSB		0x06
#define ADDR_DATA_OUT_Y_MSB		0x07
#define ADDR_DATA_OUT_Y_LSB		0x08
#define ADDR_STATUS			0x09
#define ADDR_ID_A			0x0a
#define ADDR_ID_B			0x0b
#define ADDR_ID_C			0x0c

#define HMC5883L_ADDRESS		0x1E

/* modes not changeable outside of driver */
#define HMC5883L_MODE_NORMAL		(0 << 0)  /* default */
#define HMC5883L_MODE_POSITIVE_BIAS	(1 << 0)  /* positive bias */
#define HMC5883L_MODE_NEGATIVE_BIAS	(1 << 1)  /* negative bias */

#define HMC5883L_AVERAGING_1		(0 << 5) /* conf a register */
#define HMC5883L_AVERAGING_2		(1 << 5)
#define HMC5883L_AVERAGING_4		(2 << 5)
#define HMC5883L_AVERAGING_8		(3 << 5)

#define MODE_REG_CONTINOUS_MODE		(0 << 0)
#define MODE_REG_SINGLE_MODE		(1 << 0) /* default */

#define STATUS_REG_DATA_OUT_LOCK	(1 << 1) /* page 16: set if data is only partially read, read device to reset */
#define STATUS_REG_DATA_READY		(1 << 0) /* page 16: set if all axes have valid measurements */

#define ID_A_WHO_AM_I			'H'
#define ID_B_WHO_AM_I			'4'
#define ID_C_WHO_AM_I			'3'


/* oddly, ERROR is not defined for c++ */
#ifdef ERROR
# undef ERROR
#endif
static const int ERROR = -1;

class HMC5883 : public device::I2C
{
public:
	HMC5883(int bus);
	~HMC5883();

	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);

	virtual int		open_first(struct file *filp);
	virtual int		close_last(struct file *filp);

	/**
	 * Diagnostics - print some basic information about the driver.
	 */
	void			print_info();

protected:
	virtual int		probe();

private:
	work_s			_work;
	unsigned		_measure_ticks;

	unsigned		_num_reports;
	volatile unsigned	_next_report;
	volatile unsigned	_oldest_report;
	mag_report		*_reports;
	mag_scale		_scale;
	bool			_collect_phase;

	orb_advert_t		_mag_topic;

	unsigned		_reads;
	unsigned		_measure_errors;
	unsigned		_read_errors;
	unsigned		_buf_overflows;

	perf_counter_t		_sample_perf;

	/**
	 * 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.
	 *
	 * This is the heart of the measurement state machine.  This function
	 * alternately starts a measurement, or collects the data from the
	 * previous measurement.
	 *
	 * When the interval between measurements is greater than the minimum
	 * measurement interval, a gap is inserted between collection
	 * and measurement to provide the most recent measurement possible
	 * at the next interval.
	 */
	void			cycle();

	/**
	 * 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);

	/**
	 * Write a register.
	 *
	 * @param reg		The register to write.
	 * @param val		The value to write.
	 * @return		OK on write success.
	 */
	int			write_reg(uint8_t reg, uint8_t val);

	/**
	 * Read a register.
	 *
	 * @param reg		The register to read.
	 * @param val		The value read.
	 * @return		OK on read success.
	 */
	int			read_reg(uint8_t reg, uint8_t &val);

	/**
	 * Issue a measurement command.
	 *
	 * @return		OK if the measurement command was successful.
	 */
	int			measure();

	/**
	 * Collect the result of the most recent measurement.
	 */
	int			collect();

	/**
	 * Convert a big-endian signed 16-bit value to a float.
	 *
	 * @param in		A signed 16-bit big-endian value.
	 * @return		The floating-point representation of the value.
	 */
	float			meas_to_float(uint8_t in[2]);

};

/* helper macro for handling report buffer indices */
#define INCREMENT(_x, _lim)	do { _x++; if (_x >= _lim) _x = 0; } while(0)

/*
 * Driver 'main' command.
 */
extern "C" __EXPORT int hmc5883_main(int argc, char *argv[]);


HMC5883::HMC5883(int bus) :
	I2C("HMC5883", MAG_DEVICE_PATH, bus, HMC5883L_ADDRESS, 400000),
	_measure_ticks(0),
	_num_reports(0),
	_next_report(0),
	_oldest_report(0),
	_reports(nullptr),
	_mag_topic(-1),
	_reads(0),
	_measure_errors(0),
	_read_errors(0),
	_buf_overflows(0),
	_sample_perf(perf_alloc(PC_ELAPSED, "hmc5883_read"))
{
	// enable debug() calls
	_debug_enabled = true;

	// default scaling
	_scale.x_offset = 0;
	_scale.x_scale = 1.0f / 1090.0f;	/* default range scale from counts to gauss */
	_scale.y_offset = 0;
	_scale.y_scale = 1.0f / 1090.0f;	/* default range scale from counts to gauss */
	_scale.z_offset = 0;
	_scale.z_scale = 1.0f / 1090.0f;	/* default range scale from counts to gauss */

	// work_cancel in the dtor will explode if we don't do this...
	_work.worker = nullptr;
}

HMC5883::~HMC5883()
{
	/* make sure we are truly inactive */
	stop();

	/* free any existing reports */
	if (_reports != nullptr)
		delete[] _reports;
}

int
HMC5883::init()
{
	int ret = ERROR;

	/* do I2C init (and probe) first */
	ret = I2C::init();

	if (ret != OK)
		goto out;

out:
	return ret;
}

int
HMC5883::open_first(struct file *filp)
{
	/* reset to manual-poll mode */
	_measure_ticks = 0;

	/* allocate basic report buffers */
	_num_reports = 2;
	_reports = new struct mag_report[_num_reports];
	_oldest_report = _next_report = 0;

	return OK;
}

int
HMC5883::close_last(struct file *filp)
{
	/* stop measurement */
	stop();

	/* free report buffers */
	if (_reports != nullptr) {
		delete[] _reports;
		_num_reports = 0;
	}

	_measure_ticks = 0;

	return OK;
}

int
HMC5883::probe()
{
	uint8_t data[3] = {0, 0, 0};

	_retries = 3;
	if (read_reg(ADDR_ID_A, data[0]) ||
	    read_reg(ADDR_ID_B, data[1]) ||
	    read_reg(ADDR_ID_C, data[2]))
		debug("read_reg fail");
	_retries = 1;

	if ((data[0] != ID_A_WHO_AM_I) ||
	    (data[1] != ID_B_WHO_AM_I) ||
	    (data[2] != ID_C_WHO_AM_I)) {
		debug("ID byte mismatch (%02x,%02x,%02x)", data[0], data[1], data[2]);
		return -EIO;
	}

	return OK;
}

ssize_t
HMC5883::read(struct file *filp, char *buffer, size_t buflen)
{
	unsigned count = buflen / sizeof(struct mag_report);
	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 (_oldest_report != _next_report) {
				memcpy(buffer, _reports + _oldest_report, sizeof(*_reports));
				ret += sizeof(_reports[0]);
				INCREMENT(_oldest_report, _num_reports);
			}
		}

		_reads++;

		/* if there was no data, warn the caller */
		return ret ? ret : -EAGAIN;
	}

	/* manual measurement - run one conversion */
	/* XXX really it'd be nice to lock against other readers here */
	do {
		_oldest_report = _next_report = 0;

		/* trigger a measurement */
		if (OK != measure()) {
			ret = -EIO;
			break;
		}

		/* wait for it to complete */
		usleep(HMC5883_CONVERSION_INTERVAL);

		/* run the collection phase */
		if (OK != collect()) {
			ret = -EIO;
			break;
		}

		/* state machine will have generated a report, copy it out */
		memcpy(buffer, _reports, sizeof(*_reports));
		ret = sizeof(*_reports);
		_reads++;

	} while (0);

	return ret;
}

int
HMC5883::ioctl(struct file *filp, int cmd, unsigned long arg)
{
	switch (cmd) {

	case SENSORIOCSPOLLRATE: {
			switch (arg) {

				/* switching to manual polling */
			case SENSOR_POLLRATE_MANUAL:
				stop();
				_measure_ticks = 0;
				return OK;

				/* external signalling (DRDY) not supported */
			case SENSOR_POLLRATE_EXTERNAL:

				/* zero would be bad */
			case 0:
				return -EINVAL;

				/* set default/max polling rate */
			case SENSOR_POLLRATE_MAX:
			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(HMC5883_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(HMC5883_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;
				}
			}
		}

	case SENSORIOCGPOLLRATE:
		if (_measure_ticks == 0)
			return SENSOR_POLLRATE_MANUAL;
		return (1000 / _measure_ticks);

	case SENSORIOCSQUEUEDEPTH: {
			/* add one to account for the sentinel in the ring */
			arg++;

			/* lower bound is mandatory, upper bound is a sanity check */
			if ((arg < 2) || (arg > 100))
				return -EINVAL;

			/* allocate new buffer */
			struct mag_report *buf = new struct mag_report[arg];

			if (nullptr == buf)
				return -ENOMEM;

			/* reset the measurement state machine with the new buffer, free the old */
			stop();
			delete[] _reports;
			_num_reports = arg;
			_reports = buf;
			start();

			return OK;
		}

	case SENSORIOCGQUEUEDEPTH:
		return _num_reports - 1;

	case SENSORIOCRESET:
		/* XXX implement this */
		return -EINVAL;

	case MAGIOCSSAMPLERATE:
		/* not supported, always 1 sample per poll */
		return -EINVAL;

	case MAGIOCSLOWPASS:
		/* not supported, no internal filtering */
		return -EINVAL;

	case MAGIOCSSCALE:
		/* set new scale factors */
		memcpy(&_scale, (mag_scale *)arg, sizeof(_scale));
		return 0;

	case MAGIOCGSCALE:
		/* copy out scale factors */
		memcpy((mag_scale *)arg, &_scale, sizeof(_scale));
		return 0;

	case MAGIOCCALIBRATE:
		/* XXX perform auto-calibration */
		return -EINVAL;

	default:
		/* give it to the superclass */
		return I2C::ioctl(filp, cmd, arg);
	}
}

void
HMC5883::start()
{
	/* make sure we are stopped first */
	stop();

	/* reset the report ring and state machine */
	_collect_phase = false;
	_oldest_report = _next_report = 0;

	/* schedule a cycle to start things */
	work_queue(&_work, (worker_t)&HMC5883::cycle_trampoline, this, 1);
}

void
HMC5883::stop()
{
	work_cancel(&_work);
}

void
HMC5883::cycle_trampoline(void *arg)
{
	HMC5883 *dev = (HMC5883 *)arg;

	dev->cycle();
}

void
HMC5883::cycle()
{
	/*
	 * We have to publish the mag topic in the context of the workq
	 * in order to ensure that the descriptor is valid when we go to publish.
	 *
	 * @bug	We can't really ever be torn down and restarted, since this
	 *      descriptor will never be closed and on the restart we will be
	 *      unable to re-advertise.
	 */
	if (_mag_topic == -1) {
		struct mag_report m;

		/* if this fails (e.g. no object in the system) we will cope */
		memset(&m, 0, sizeof(m));
		_mag_topic = orb_advertise(ORB_ID(sensor_mag), &m);

		if (_mag_topic < 0)
			debug("failed to create sensor_mag object");
	}

	/* collection phase? */
	if (_collect_phase) {

		/* perform collection */
		if (OK != collect()) {
			log("FATAL collection error - restarting\n");
			start();
			return;
		}

		/* next phase is measurement */
		_collect_phase = false;

		/*
		 * Is there a collect->measure gap?
		 */
		if (_measure_ticks > USEC2TICK(HMC5883_CONVERSION_INTERVAL)) {

			/* schedule a fresh cycle call when we are ready to measure again */
			work_queue(&_work,
				   (worker_t)&HMC5883::cycle_trampoline,
				   this,
				   _measure_ticks - USEC2TICK(HMC5883_CONVERSION_INTERVAL));

			return;
		}
	}

	/* measurement phase */
	if (OK != measure()) {
		log("FATAL measure error - restarting\n");
		start();
	}

	/* next phase is collection */
	_collect_phase = true;

	/* schedule a fresh cycle call when the measurement is done */
	work_queue(&_work,
		   (worker_t)&HMC5883::cycle_trampoline,
		   this,
		   USEC2TICK(HMC5883_CONVERSION_INTERVAL));
}

int
HMC5883::measure()
{
	int ret;

	/*
	 * Send the command to begin a measurement.
	 */
	ret = write_reg(ADDR_MODE, MODE_REG_SINGLE_MODE);

	if (OK != ret)
		_measure_errors++;

	return ret;
}

int
HMC5883::collect()
{
#pragma pack(push, 1)
	struct { /* status register and data as read back from the device */
		uint8_t		x[2];
		uint8_t		y[2];
		uint8_t		z[2];
	}	hmc_report;
#pragma pack(pop)
	struct {
		int16_t		x, y, z;
	} report;
	int	ret = -EIO;
	uint8_t	cmd;


	perf_begin(_sample_perf);

	/* this should be fairly close to the end of the measurement, so the best approximation of the time */
	_reports[_next_report].timestamp = hrt_absolute_time();

	/*
	 * @note  We could read the status register here, which could tell us that
	 *        we were too early and that the output registers are still being
	 *        written.  In the common case that would just slow us down, and
	 *        we're better off just never being early.
	 */

	/* get measurements from the device */
	cmd = ADDR_DATA_OUT_X_MSB;
	ret = transfer(&cmd, 1, (uint8_t *)&hmc_report, sizeof(hmc_report));

	if (ret != OK) {
		debug("data/status read error");
		goto out;
	}

	/* swap the data we just received */
	report.x = ((int16_t)hmc_report.x[0] << 8) + hmc_report.x[1];
	report.y = ((int16_t)hmc_report.y[0] << 8) + hmc_report.y[1];
	report.z = ((int16_t)hmc_report.z[0] << 8) + hmc_report.z[1];

	/*
	 * If any of the values are -4096, there was an internal math error in the sensor.
	 * Generalise this to a simple range check that will also catch some bit errors.
	 */
	if ((abs(report.x) > 2048) ||
	    (abs(report.y) > 2048) ||
	    (abs(report.z) > 2048))
		goto out;

	/* scale values for output */
	_reports[_next_report].x = report.x * _scale.x_scale + _scale.x_offset;
	_reports[_next_report].y = report.y * _scale.y_scale + _scale.y_offset;
	_reports[_next_report].z = report.z * _scale.z_scale + _scale.z_offset;

	/* publish it */
	orb_publish(ORB_ID(sensor_mag), _mag_topic, &_reports[_next_report]);

	/* post a report to the ring - note, not locked */
	INCREMENT(_next_report, _num_reports);

	/* if we are running up against the oldest report, toss it */
	if (_next_report == _oldest_report) {
		_buf_overflows++;
		INCREMENT(_oldest_report, _num_reports);
	}

	/* notify anyone waiting for data */
	poll_notify(POLLIN);

	ret = OK;

out:
	perf_end(_sample_perf);
	return ret;
}

int
HMC5883::write_reg(uint8_t reg, uint8_t val)
{
	uint8_t cmd[] = { reg, val };

	return transfer(&cmd[0], 2, nullptr, 0);
}

int
HMC5883::read_reg(uint8_t reg, uint8_t &val)
{
	return transfer(&reg, 1, &val, 1);
}

float
HMC5883::meas_to_float(uint8_t in[2])
{
	union {
		uint8_t	b[2];
		int16_t	w;
	} u;

	u.b[0] = in[1];
	u.b[1] = in[0];

	return (float) u.w;
}

void
HMC5883::print_info()
{
	printf("reads:          %u\n", _reads);
	printf("measure errors: %u\n", _measure_errors);
	printf("read errors:    %u\n", _read_errors);
	printf("read overflows: %u\n", _buf_overflows);
	printf("poll interval:  %u ticks\n", _measure_ticks);
	printf("report queue:   %u (%u/%u @ %p)\n",
	       _num_reports, _oldest_report, _next_report, _reports);
}

/**
 * Local functions in support of the shell command.
 */
namespace hmc5883
{

/* oddly, ERROR is not defined for c++ */
#ifdef ERROR
# undef ERROR
#endif
const int ERROR = -1;

HMC5883	*g_dev;

void	start();
void	test();
void	reset();
void	info();

/**
 * Start the driver.
 */
void
start()
{
	int fd;

	if (g_dev != nullptr)
		errx(1, "already started");

	/* create the driver */
	/* XXX HORRIBLE hack - the bus number should not come from here */
	g_dev = new HMC5883(2);

	if (g_dev == nullptr)
		goto fail;

	if (OK != g_dev->init())
		goto fail;

	/* set the poll rate to default, starts automatic data collection */
	fd = open(MAG_DEVICE_PATH, O_RDONLY);
	if (fd < 0)
		goto fail;
	if (ioctl(fd, SENSORIOCSPOLLRATE, SENSOR_POLLRATE_DEFAULT) < 0)
		goto fail;
	exit(0);

fail:
	if (g_dev != nullptr) {
		delete g_dev;
		g_dev = nullptr;
	}
	errx(1, "driver start failed");
}

/**
 * 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 mag_report report;
	ssize_t sz;
	int ret;

	int fd = open(MAG_DEVICE_PATH, O_RDONLY);
	if (fd < 0)
		err(1, "%s open failed (try 'hmc5883 start' if the driver is not running", MAG_DEVICE_PATH);

	/* do a simple demand read */
	sz = read(fd, &report, sizeof(report));
	if (sz != sizeof(report))
		err(1, "immediate read failed");

	warnx("single read");
	warnx("measurement: %.6f  %.6f  %.6f", report.x, report.y, report.z);
	warnx("time:        %lld", report.timestamp);

	/* set the queue depth to 10 */
	if (OK != ioctl(fd, SENSORIOCSQUEUEDEPTH, 10))
		errx(1, "failed to set queue depth");

	/* start the sensor polling at 2Hz */
	if (OK != ioctl(fd, SENSORIOCSPOLLRATE, 2))
		errx(1, "failed to set 2Hz poll rate");

	/* read the sensor 5x and report each value */
	for (unsigned i = 0; i < 5; 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");

		warnx("periodic read %u", i);
		warnx("measurement: %.6f  %.6f  %.6f", report.x, report.y, report.z);
		warnx("time:        %lld", report.timestamp);
	}

	errx(0, "PASS");
}

/**
 * Reset the driver.
 */
void
reset()
{
	int fd = open(MAG_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);
}

} // namespace

int
hmc5883_main(int argc, char *argv[])
{
	/*
	 * Start/load the driver.
	 */
	if (!strcmp(argv[1], "start"))
		hmc5883::start();

	/*
	 * Test the driver/device.
	 */
	if (!strcmp(argv[1], "test"))
		hmc5883::test();

	/*
	 * Reset the driver.
	 */
	if (!strcmp(argv[1], "reset"))
		hmc5883::reset();

	/*
	 * Print driver information.
	 */
	if (!strcmp(argv[1], "info"))
		hmc5883::info();

	errx(1, "unrecognised command, try 'start', 'test', 'reset' or 'info'");
}