PX4-Autopilot/src/drivers/ms5611/ms5611.cpp

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 *
 *   Copyright (C) 2012-2013 PX4 Development Team. All rights reserved.
 *
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 * modification, are permitted provided that the following conditions
 * are met:
 *
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/**
 * @file ms5611.cpp
 * Driver for the MS5611 barometric pressure sensor connected via I2C or SPI.
 */

#include <nuttx/config.h>

#include <sys/types.h>
#include <stdint.h>
#include <stdbool.h>
#include <stdlib.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/board.h>

#include <drivers/device/device.h>
#include <drivers/drv_baro.h>
#include <drivers/drv_hrt.h>
#include <drivers/device/ringbuffer.h>

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

#include "ms5611.h"

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

#ifndef CONFIG_SCHED_WORKQUEUE
# error This requires CONFIG_SCHED_WORKQUEUE.
#endif

/* helper macro for handling report buffer indices */
#define INCREMENT(_x, _lim)	do { __typeof__(_x) _tmp = _x+1; if (_tmp >= _lim) _tmp = 0; _x = _tmp; } while(0)

/* helper macro for arithmetic - returns the square of the argument */
#define POW2(_x)		((_x) * (_x))

/*
 * MS5611 internal constants and data structures.
 */

/* internal conversion time: 9.17 ms, so should not be read at rates higher than 100 Hz */
#define MS5611_CONVERSION_INTERVAL	10000	/* microseconds */
#define MS5611_MEASUREMENT_RATIO	3	/* pressure measurements per temperature measurement */

class MS5611 : public device::CDev
{
public:
	MS5611(device::Device *interface, ms5611::prom_u &prom_buf);
	~MS5611();

	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:
	Device			*_interface;

	ms5611::prom_s		_prom;

	struct work_s		_work;
	unsigned		_measure_ticks;

	RingBuffer<struct baro_report> *_reports;

	bool			_collect_phase;
	unsigned		_measure_phase;

	/* intermediate temperature values per MS5611 datasheet */
	int32_t			_TEMP;
	int64_t			_OFF;
	int64_t			_SENS;

	/* altitude conversion calibration */
	unsigned		_msl_pressure;	/* in kPa */

	orb_advert_t		_baro_topic;

	perf_counter_t		_sample_perf;
	perf_counter_t		_measure_perf;
	perf_counter_t		_comms_errors;
	perf_counter_t		_buffer_overflows;

	/**
	 * Initialize 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_cycle();

	/**
	 * Stop the automatic measurement state machine.
	 */
	void			stop_cycle();

	/**
	 * 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);

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

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

/*
 * Driver 'main' command.
 */
extern "C" __EXPORT int ms5611_main(int argc, char *argv[]);

MS5611::MS5611(device::Device *interface, ms5611::prom_u &prom_buf) :
	CDev("MS5611", BARO_DEVICE_PATH),
	_interface(interface),
	_prom(prom_buf.s),
	_measure_ticks(0),
	_reports(nullptr),
	_collect_phase(false),
	_measure_phase(0),
	_TEMP(0),
	_OFF(0),
	_SENS(0),
	_msl_pressure(101325),
	_baro_topic(-1),
	_sample_perf(perf_alloc(PC_ELAPSED, "ms5611_read")),
	_measure_perf(perf_alloc(PC_ELAPSED, "ms5611_measure")),
	_comms_errors(perf_alloc(PC_COUNT, "ms5611_comms_errors")),
	_buffer_overflows(perf_alloc(PC_COUNT, "ms5611_buffer_overflows"))
{
	// work_cancel in stop_cycle called from the dtor will explode if we don't do this...
	memset(&_work, 0, sizeof(_work));
}

MS5611::~MS5611()
{
	/* make sure we are truly inactive */
	stop_cycle();

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

	// free perf counters
	perf_free(_sample_perf);
	perf_free(_measure_perf);
	perf_free(_comms_errors);
	perf_free(_buffer_overflows);

	delete _interface;
}

int
MS5611::init()
{
	int ret;

	ret = CDev::init();
	if (ret != OK) {
		debug("CDev init failed");
		goto out;
	}

	/* allocate basic report buffers */
	_reports = new RingBuffer<struct baro_report>(2);

	if (_reports == nullptr) {
		debug("can't get memory for reports");
		ret = -ENOMEM;
		goto out;
	}

	/* get a publish handle on the baro topic */
	struct baro_report zero_report;
	memset(&zero_report, 0, sizeof(zero_report));
	_baro_topic = orb_advertise(ORB_ID(sensor_baro), &zero_report);

	if (_baro_topic < 0) {
		debug("failed to create sensor_baro object");
		ret = -ENOSPC;
		goto out;
	}

	ret = OK;
out:
	return ret;
}

ssize_t
MS5611::read(struct file *filp, char *buffer, size_t buflen)
{
	unsigned count = buflen / sizeof(struct baro_report);
	struct baro_report *brp = reinterpret_cast<struct baro_report *>(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(*brp)) {
				ret += sizeof(*brp);
				brp++;
			}
		}

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

	/* manual measurement - run one conversion */
	do {
		_measure_phase = 0;
		_reports->flush();

		/* do temperature first */
		if (OK != measure()) {
			ret = -EIO;
			break;
		}

		usleep(MS5611_CONVERSION_INTERVAL);

		if (OK != collect()) {
			ret = -EIO;
			break;
		}

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

		usleep(MS5611_CONVERSION_INTERVAL);

		if (OK != collect()) {
			ret = -EIO;
			break;
		}

		/* state machine will have generated a report, copy it out */
		if (_reports->get(*brp))
			ret = sizeof(*brp);

	} while (0);

	return ret;
}

int
MS5611::ioctl(struct file *filp, int cmd, unsigned long arg)
{
	switch (cmd) {

	case SENSORIOCSPOLLRATE: {
			switch (arg) {

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

				/* external signalling 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(MS5611_CONVERSION_INTERVAL);

					/* if we need to start the poll state machine, do it */
					if (want_start)
						start_cycle();

					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(MS5611_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_cycle();

					return OK;
				}
			}
		}

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

		return (1000 / _measure_ticks);

	case SENSORIOCSQUEUEDEPTH: {
		/* lower bound is mandatory, upper bound is a sanity check */
		if ((arg < 1) || (arg > 100))
			return -EINVAL;

		irqstate_t flags = irqsave();
		if (!_reports->resize(arg)) {
			irqrestore(flags);
			return -ENOMEM;
		}
		irqrestore(flags);		
		return OK;
	}

	case SENSORIOCGQUEUEDEPTH:
		return _reports->size();

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

	case BAROIOCSMSLPRESSURE:

		/* range-check for sanity */
		if ((arg < 80000) || (arg > 120000))
			return -EINVAL;

		_msl_pressure = arg;
		return OK;

	case BAROIOCGMSLPRESSURE:
		return _msl_pressure;

	default:
		break;
	}

	/* give it to the bus-specific superclass */
	// return bus_ioctl(filp, cmd, arg);
	return CDev::ioctl(filp, cmd, arg);
}

void
MS5611::start_cycle()
{

	/* reset the report ring and state machine */
	_collect_phase = false;
	_measure_phase = 0;
	_reports->flush();

	/* schedule a cycle to start things */
	work_queue(HPWORK, &_work, (worker_t)&MS5611::cycle_trampoline, this, 1);
}

void
MS5611::stop_cycle()
{
	work_cancel(HPWORK, &_work);
}

void
MS5611::cycle_trampoline(void *arg)
{
	MS5611 *dev = reinterpret_cast<MS5611 *>(arg);

	dev->cycle();
}

void
MS5611::cycle()
{
	int ret;

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

		/* perform collection */
		ret = collect();
		if (ret != OK) {
			if (ret == -6) {
				/*
				 * The ms5611 seems to regularly fail to respond to
				 * its address; this happens often enough that we'd rather not
				 * spam the console with a message for this.
				 */
			} else {
				//log("collection error %d", ret);
			}
			/* reset the collection state machine and try again */
			start_cycle();
			return;
		}

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

		/*
		 * Is there a collect->measure gap?
		 * Don't inject one after temperature measurements, so we can keep
		 * doing pressure measurements at something close to the desired rate.
		 */
		if ((_measure_phase != 0) &&
		    (_measure_ticks > USEC2TICK(MS5611_CONVERSION_INTERVAL))) {

			/* schedule a fresh cycle call when we are ready to measure again */
			work_queue(HPWORK,
				   &_work,
				   (worker_t)&MS5611::cycle_trampoline,
				   this,
				   _measure_ticks - USEC2TICK(MS5611_CONVERSION_INTERVAL));

			return;
		}
	}

	/* measurement phase */
	ret = measure();
	if (ret != OK) {
		//log("measure error %d", ret);
		/* reset the collection state machine and try again */
		start_cycle();
		return;
	}

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

	/* schedule a fresh cycle call when the measurement is done */
	work_queue(HPWORK,
		   &_work,
		   (worker_t)&MS5611::cycle_trampoline,
		   this,
		   USEC2TICK(MS5611_CONVERSION_INTERVAL));
}

int
MS5611::measure()
{
	int ret;

	perf_begin(_measure_perf);

	/*
	 * In phase zero, request temperature; in other phases, request pressure.
	 */
	unsigned addr = (_measure_phase == 0) ? ADDR_CMD_CONVERT_D2 : ADDR_CMD_CONVERT_D1;

	/*
	 * Send the command to begin measuring.
	 */
	ret = _interface->ioctl(IOCTL_MEASURE, addr);
	if (OK != ret)
		perf_count(_comms_errors);

	perf_end(_measure_perf);

	return ret;
}

int
MS5611::collect()
{
	int ret;
	uint32_t raw;

	perf_begin(_sample_perf);

	struct baro_report report;
	/* this should be fairly close to the end of the conversion, so the best approximation of the time */
	report.timestamp = hrt_absolute_time();

	/* read the most recent measurement - read offset/size are hardcoded in the interface */
	ret = _interface->read(0, (void *)&raw, 0);
	if (ret < 0) {
		perf_count(_comms_errors);
		perf_end(_sample_perf);
		return ret;
	}

	/* handle a measurement */
	if (_measure_phase == 0) {

		/* temperature offset (in ADC units) */
		int32_t dT = (int32_t)raw - ((int32_t)_prom.c5_reference_temp << 8);

		/* absolute temperature in centidegrees - note intermediate value is outside 32-bit range */
		_TEMP = 2000 + (int32_t)(((int64_t)dT * _prom.c6_temp_coeff_temp) >> 23);

		/* base sensor scale/offset values */
		_SENS = ((int64_t)_prom.c1_pressure_sens << 15) + (((int64_t)_prom.c3_temp_coeff_pres_sens * dT) >> 8);
		_OFF  = ((int64_t)_prom.c2_pressure_offset << 16) + (((int64_t)_prom.c4_temp_coeff_pres_offset * dT) >> 7);

		/* temperature compensation */
		if (_TEMP < 2000) {

			int32_t T2 = POW2(dT) >> 31;

			int64_t f = POW2((int64_t)_TEMP - 2000);
			int64_t OFF2 = 5 * f >> 1;
			int64_t SENS2 = 5 * f >> 2;

			if (_TEMP < -1500) {
				int64_t f2 = POW2(_TEMP + 1500);
				OFF2 += 7 * f2;
				SENS2 += 11 * f2 >> 1;
			}

			_TEMP -= T2;
			_OFF  -= OFF2;
			_SENS -= SENS2;
		}

	} else {

		/* pressure calculation, result in Pa */
		int32_t P = (((raw * _SENS) >> 21) - _OFF) >> 15;

		/* generate a new report */
		report.temperature = _TEMP / 100.0f;
		report.pressure = P / 100.0f;		/* convert to millibar */

		/* altitude calculations based on http://www.kansasflyer.org/index.asp?nav=Avi&sec=Alti&tab=Theory&pg=1 */

		/*
		 * PERFORMANCE HINT:
		 *
		 * The single precision calculation is 50 microseconds faster than the double
		 * precision variant. It is however not obvious if double precision is required.
		 * Pending more inspection and tests, we'll leave the double precision variant active.
		 *
		 * Measurements:
		 * 	double precision: ms5611_read: 992 events, 258641us elapsed, min 202us max 305us
		 *	single precision: ms5611_read: 963 events, 208066us elapsed, min 202us max 241us
		 */

		/* tropospheric properties (0-11km) for standard atmosphere */
		const double T1 = 15.0 + 273.15;	/* temperature at base height in Kelvin */
		const double a  = -6.5 / 1000;	/* temperature gradient in degrees per metre */
		const double g  = 9.80665;	/* gravity constant in m/s/s */
		const double R  = 287.05;	/* ideal gas constant in J/kg/K */

		/* current pressure at MSL in kPa */
		double p1 = _msl_pressure / 1000.0;

		/* measured pressure in kPa */
		double p = P / 1000.0;

		/*
		 * Solve:
		 *
		 *     /        -(aR / g)     \
		 *    | (p / p1)          . T1 | - T1
		 *     \                      /
		 * h = -------------------------------  + h1
		 *                   a
		 */
		report.altitude = (((pow((p / p1), (-(a * R) / g))) * T1) - T1) / a;

		/* publish it */
		orb_publish(ORB_ID(sensor_baro), _baro_topic, &report);

		if (_reports->force(report)) {
			perf_count(_buffer_overflows);
		}

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

	/* update the measurement state machine */
	INCREMENT(_measure_phase, MS5611_MEASUREMENT_RATIO + 1);

	perf_end(_sample_perf);

	return OK;
}

void
MS5611::print_info()
{
	perf_print_counter(_sample_perf);
	perf_print_counter(_comms_errors);
	perf_print_counter(_buffer_overflows);
	printf("poll interval:  %u ticks\n", _measure_ticks);
	_reports->print_info("report queue");
	printf("TEMP:           %d\n", _TEMP);
	printf("SENS:           %lld\n", _SENS);
	printf("OFF:            %lld\n", _OFF);
	printf("MSL pressure:   %10.4f\n", (double)(_msl_pressure / 100.f));

	printf("factory_setup             %u\n", _prom.factory_setup);
	printf("c1_pressure_sens          %u\n", _prom.c1_pressure_sens);
	printf("c2_pressure_offset        %u\n", _prom.c2_pressure_offset);
	printf("c3_temp_coeff_pres_sens   %u\n", _prom.c3_temp_coeff_pres_sens);
	printf("c4_temp_coeff_pres_offset %u\n", _prom.c4_temp_coeff_pres_offset);
	printf("c5_reference_temp         %u\n", _prom.c5_reference_temp);
	printf("c6_temp_coeff_temp        %u\n", _prom.c6_temp_coeff_temp);
	printf("serial_and_crc            %u\n", _prom.serial_and_crc);
}

/**
 * Local functions in support of the shell command.
 */
namespace ms5611
{

MS5611	*g_dev;

void	start();
void	test();
void	reset();
void	info();
void	calibrate(unsigned altitude);

/**
 * MS5611 crc4 cribbed from the datasheet
 */
bool
crc4(uint16_t *n_prom)
{
	int16_t cnt;
	uint16_t n_rem;
	uint16_t crc_read;
	uint8_t n_bit;

	n_rem = 0x00;

	/* save the read crc */
	crc_read = n_prom[7];

	/* remove CRC byte */
	n_prom[7] = (0xFF00 & (n_prom[7]));

	for (cnt = 0; cnt < 16; cnt++) {
		/* uneven bytes */
		if (cnt & 1) {
			n_rem ^= (uint8_t)((n_prom[cnt >> 1]) & 0x00FF);

		} else {
			n_rem ^= (uint8_t)(n_prom[cnt >> 1] >> 8);
		}

		for (n_bit = 8; n_bit > 0; n_bit--) {
			if (n_rem & 0x8000) {
				n_rem = (n_rem << 1) ^ 0x3000;

			} else {
				n_rem = (n_rem << 1);
			}
		}
	}

	/* final 4 bit remainder is CRC value */
	n_rem = (0x000F & (n_rem >> 12));
	n_prom[7] = crc_read;

	/* return true if CRCs match */
	return (0x000F & crc_read) == (n_rem ^ 0x00);
}


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

	if (g_dev != nullptr)
		/* if already started, the still command succeeded */
		errx(0, "already started");

	device::Device *interface = nullptr;

	/* create the driver, try SPI first, fall back to I2C if unsuccessful */
	if (MS5611_spi_interface != nullptr)
		interface = MS5611_spi_interface(prom_buf);
	if (interface == nullptr && (MS5611_i2c_interface != nullptr))
		interface = MS5611_i2c_interface(prom_buf);

	if (interface == nullptr)
		errx(1, "failed to allocate an interface");

	if (interface->init() != OK) {
		delete interface;
		errx(1, "interface init failed");
	}

	g_dev = new MS5611(interface, prom_buf);
	if (g_dev == nullptr) {
		delete interface;
		errx(1, "failed to allocate driver");
	}
	if (g_dev->init() != OK)
		goto fail;

	/* set the poll rate to default, starts automatic data collection */
	fd = open(BARO_DEVICE_PATH, O_RDONLY);
	if (fd < 0) {
		warnx("can't open baro device");
		goto fail;
	}
	if (ioctl(fd, SENSORIOCSPOLLRATE, SENSOR_POLLRATE_DEFAULT) < 0) {
		warnx("failed setting default poll rate");
		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 baro_report report;
	ssize_t sz;
	int ret;

	int fd = open(BARO_DEVICE_PATH, O_RDONLY);

	if (fd < 0)
		err(1, "%s open failed (try 'ms5611 start' if the driver is not running)", BARO_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("pressure:    %10.4f", (double)report.pressure);
	warnx("altitude:    %11.4f", (double)report.altitude);
	warnx("temperature: %8.4f", (double)report.temperature);
	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("pressure:    %10.4f", (double)report.pressure);
		warnx("altitude:    %11.4f", (double)report.altitude);
		warnx("temperature: %8.4f", (double)report.temperature);
		warnx("time:        %lld", report.timestamp);
	}

	errx(0, "PASS");
}

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

/**
 * Calculate actual MSL pressure given current altitude
 */
void
calibrate(unsigned altitude)
{
	struct baro_report report;
	float	pressure;
	float	p1;

	int fd = open(BARO_DEVICE_PATH, O_RDONLY);

	if (fd < 0)
		err(1, "%s open failed (try 'ms5611 start' if the driver is not running)", BARO_DEVICE_PATH);

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

	/* average a few measurements */
	pressure = 0.0f;

	for (unsigned i = 0; i < 20; i++) {
		struct pollfd fds;
		int ret;
		ssize_t sz;

		/* wait for data to be ready */
		fds.fd = fd;
		fds.events = POLLIN;
		ret = poll(&fds, 1, 1000);

		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, "sensor read failed");

		pressure += report.pressure;
	}

	pressure /= 20;		/* average */
	pressure /= 10;		/* scale from millibar to kPa */

	/* tropospheric properties (0-11km) for standard atmosphere */
	const float T1 = 15.0 + 273.15;	/* temperature at base height in Kelvin */
	const float a  = -6.5 / 1000;	/* temperature gradient in degrees per metre */
	const float g  = 9.80665f;	/* gravity constant in m/s/s */
	const float R  = 287.05f;	/* ideal gas constant in J/kg/K */

	warnx("averaged pressure %10.4fkPa at %um", (double)pressure, altitude);

	p1 = pressure * (powf(((T1 + (a * (float)altitude)) / T1), (g / (a * R))));

	warnx("calculated MSL pressure %10.4fkPa", (double)p1);

	/* save as integer Pa */
	p1 *= 1000.0f;

	if (ioctl(fd, BAROIOCSMSLPRESSURE, (unsigned long)p1) != OK)
		err(1, "BAROIOCSMSLPRESSURE");

	exit(0);
}

} // namespace

int
ms5611_main(int argc, char *argv[])
{
	/*
	 * Start/load the driver.
	 */
	if (!strcmp(argv[1], "start"))
		ms5611::start();

	/*
	 * Test the driver/device.
	 */
	if (!strcmp(argv[1], "test"))
		ms5611::test();

	/*
	 * Reset the driver.
	 */
	if (!strcmp(argv[1], "reset"))
		ms5611::reset();

	/*
	 * Print driver information.
	 */
	if (!strcmp(argv[1], "info"))
		ms5611::info();

	/*
	 * Perform MSL pressure calibration given an altitude in metres
	 */
	if (!strcmp(argv[1], "calibrate")) {
		if (argc < 2)
			errx(1, "missing altitude");

		long altitude = strtol(argv[2], nullptr, 10);

		ms5611::calibrate(altitude);
	}

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