ms5837.c

/**
 * \file ms5837.c
 *
 * \brief MS5837 Temperature sensor driver source file
 *
 * Copyright (c) 2016 Measurement Specialties. All rights reserved.
 *
 * For details on programming, refer to ms5837 datasheet :
 * http://meas-spec.com/downloads/MS5837-30BA.pdf
 *
 */

#include "ms5837.h"

  /**
  * The header "i2c.h" has to be implemented for your own platform to 
  * conform the following protocol :
  *
  * enum i2c_transfer_direction {
  * 	I2C_TRANSFER_WRITE = 0,
  * 	I2C_TRANSFER_READ  = 1,
  * };
  * 
  * enum status_code {
  * 	STATUS_OK           = 0x00,
  * 	STATUS_ERR_OVERFLOW	= 0x01,
  *		STATUS_ERR_TIMEOUT  = 0x02,
  * };
  * 
  * struct i2c_master_packet {
  * 	// Address to slave device
  * 	uint16_t address;
  * 	// Length of data array
  * 	uint16_t data_length;
  * 	// Data array containing all data to be transferred
  * 	uint8_t *data;
  * };
  * 
  * void i2c_master_init(void);
  * enum status_code i2c_master_read_packet_wait(struct i2c_master_packet *const packet);
  * enum status_code i2c_master_write_packet_wait(struct i2c_master_packet *const packet);
  * enum status_code i2c_master_write_packet_wait_no_stop(struct i2c_master_packet *const packet);
  */
#include "i2c.h"

#ifdef __cplusplus
extern "C" {
#endif

// Constants

// MS5837 device address
#define MS5837_ADDR													0x76 //0b1110110

// MS5837 device commands
#define MS5837_RESET_COMMAND										0x1E
#define MS5837_START_PRESSURE_ADC_CONVERSION						0x40
#define MS5837_START_TEMPERATURE_ADC_CONVERSION						0x50
#define MS5837_READ_ADC												0x00

#define MS5837_CONVERSION_OSR_MASK									0x0F

#define MS5837_CONVERSION_TIME_OSR_256								1000
#define MS5837_CONVERSION_TIME_OSR_512								2000
#define MS5837_CONVERSION_TIME_OSR_1024								3000
#define MS5837_CONVERSION_TIME_OSR_2048								5000
#define MS5837_CONVERSION_TIME_OSR_4096								9000
#define MS5837_CONVERSION_TIME_OSR_8192								17000

// MS5837 commands
#define MS5837_PROM_ADDRESS_READ_ADDRESS_0							0xA0
#define MS5837_PROM_ADDRESS_READ_ADDRESS_1							0xA2
#define MS5837_PROM_ADDRESS_READ_ADDRESS_2							0xA4
#define MS5837_PROM_ADDRESS_READ_ADDRESS_3							0xA6
#define MS5837_PROM_ADDRESS_READ_ADDRESS_4							0xA8
#define MS5837_PROM_ADDRESS_READ_ADDRESS_5							0xAA
#define MS5837_PROM_ADDRESS_READ_ADDRESS_6							0xAC
#define MS5837_PROM_ADDRESS_READ_ADDRESS_7							0xAE

// Coefficients indexes for temperature and pressure computation
#define MS5837_CRC_INDEX											0
#define MS5837_PRESSURE_SENSITIVITY_INDEX							1 
#define MS5837_PRESSURE_OFFSET_INDEX								2
#define MS5837_TEMP_COEFF_OF_PRESSURE_SENSITIVITY_INDEX				3
#define MS5837_TEMP_COEFF_OF_PRESSURE_OFFSET_INDEX					4
#define MS5837_REFERENCE_TEMPERATURE_INDEX							5
#define MS5837_TEMP_COEFF_OF_TEMPERATURE_INDEX						6
#define MS5837_COEFFICIENT_NUMBERS									7

// Static functions
static enum ms5837_status ms5837_write_command(uint8_t);
static enum ms5837_status ms5837_read_eeprom_coeff(uint8_t, uint16_t*);
static enum ms5837_status ms5837_read_eeprom(void);
static enum ms5837_status ms5837_conversion_and_read_adc( uint8_t, uint32_t *);
static bool ms5837_crc_check (uint16_t *n_prom, uint8_t crc);

enum ms5837_resolution_osr ms5837_resolution_osr;
static uint16_t eeprom_coeff[MS5837_COEFFICIENT_NUMBERS+1];
static uint32_t conversion_time[6] = {	MS5837_CONVERSION_TIME_OSR_256,
										MS5837_CONVERSION_TIME_OSR_512,
										MS5837_CONVERSION_TIME_OSR_1024,
										MS5837_CONVERSION_TIME_OSR_2048,
										MS5837_CONVERSION_TIME_OSR_4096,
										MS5837_CONVERSION_TIME_OSR_8192};

// Default value to ensure coefficients are read before converting temperature
bool ms5837_coeff_read = false;

/**
 * \brief Configures the SERCOM I2C master to be used with the MS5837 device.
 */
void ms5837_init(void)
{
	ms5837_resolution_osr = ms5837_resolution_osr_8192;
	
    /* Initialize and enable device with config. */
	i2c_master_init();
}

/**
 * \brief Check whether MS5837 device is connected
 *
 * \return bool : status of MS5837
 *       - true : Device is present
 *       - false : Device is not acknowledging I2C address
  */
bool ms5837_is_connected(void)
{
	enum status_code i2c_status;
	
	struct i2c_master_packet transfer = {
		.address     = MS5837_ADDR,
		.data_length = 0,
		.data        = NULL,
	};
	/* Do the transfer */
	i2c_status = i2c_master_write_packet_wait(&transfer);
	if( i2c_status != STATUS_OK)
		return false;
	
	return true;
}
	
/**
 * \brief Reset the MS5837 device
 *
 * \return ms5837_status : status of MS5837
 *       - ms5837_status_ok : I2C transfer completed successfully
 *       - ms5837_status_i2c_transfer_error : Problem with i2c transfer
 *       - ms5837_status_no_i2c_acknowledge : I2C did not acknowledge
 */
enum ms5837_status  ms5837_reset(void)
{
	return ms5837_write_command(MS5837_RESET_COMMAND);
}

/**
 * \brief Set  ADC resolution.
 *
 * \param[in] ms5837_resolution_osr : Resolution requested
 *
 */
void ms5837_set_resolution(enum ms5837_resolution_osr res)
{
	ms5837_resolution_osr = res;
	return;
}

/**
 * \brief Writes the MS5837 8-bits command with the value passed
 *
 * \param[in] uint8_t : Command value to be written.
 *
 * \return ms5837_status : status of MS5837
 *       - ms5837_status_ok : I2C transfer completed successfully
 *       - ms5837_status_i2c_transfer_error : Problem with i2c transfer
 *       - ms5837_status_no_i2c_acknowledge : I2C did not acknowledge
 */
enum ms5837_status ms5837_write_command( uint8_t cmd)
{
	enum status_code i2c_status;
	uint8_t data[1];
		
	data[0] = cmd;
		
	struct i2c_master_packet transfer = {
		.address     = MS5837_ADDR,
		.data_length = 1,
		.data        = data,
	};
	/* Do the transfer */
	i2c_status = i2c_master_write_packet_wait(&transfer);
	if( i2c_status == STATUS_ERR_OVERFLOW )
		return ms5837_status_no_i2c_acknowledge;
	if( i2c_status != STATUS_OK)
		return ms5837_status_i2c_transfer_error;
	
	return ms5837_status_ok;
}

/**
 * \brief Reads the ms5837 EEPROM coefficient stored at address provided.
 *
 * \param[in] uint8_t : Address of coefficient in EEPROM
 * \param[out] uint16_t* : Value read in EEPROM
 *
 * \return ms5837_status : status of MS5837
 *       - ms5837_status_ok : I2C transfer completed successfully
 *       - ms5837_status_i2c_transfer_error : Problem with i2c transfer
 *       - ms5837_status_no_i2c_acknowledge : I2C did not acknowledge
 *       - ms5837_status_crc_error : CRC check error on the coefficients
 */
enum ms5837_status ms5837_read_eeprom_coeff(uint8_t command, uint16_t *coeff)
{
	enum ms5837_status status;
	enum status_code i2c_status;
	uint8_t buffer[2];
	
	buffer[0] = 0;
	buffer[1] = 0;

	/* Read data */
	struct i2c_master_packet read_transfer = {
		.address     = MS5837_ADDR,
		.data_length = 2,
		.data        = buffer,
	};
	
	// Send the conversion command
	status = ms5837_write_command(command);
	if(status != ms5837_status_ok)
		return status;
	
	i2c_status = i2c_master_read_packet_wait(&read_transfer);
	if( i2c_status == STATUS_ERR_OVERFLOW )
		return ms5837_status_no_i2c_acknowledge;
	if( i2c_status != STATUS_OK)
		return ms5837_status_i2c_transfer_error;
		
	*coeff = (buffer[0] << 8) | buffer[1];
    
    if (*coeff == 0)
        return ms5837_status_i2c_transfer_error;
	
	return ms5837_status_ok;	
}

/**
 * \brief Reads the ms5837 EEPROM coefficients to store them for computation.
 *
 * \return ms5837_status : status of MS5837
 *       - ms5837_status_ok : I2C transfer completed successfully
 *       - ms5837_status_i2c_transfer_error : Problem with i2c transfer
 *       - ms5837_status_no_i2c_acknowledge : I2C did not acknowledge
 *       - ms5837_status_crc_error : CRC check error on the coefficients
 */
enum ms5837_status ms5837_read_eeprom(void)
{
	enum ms5837_status status;
	uint8_t i;
	
	for( i=0 ; i< MS5837_COEFFICIENT_NUMBERS ; i++)
	{
		status = ms5837_read_eeprom_coeff( MS5837_PROM_ADDRESS_READ_ADDRESS_0 + i*2, eeprom_coeff+i);
		if(status != ms5837_status_ok)
			return status;
	}
    
	if( !ms5837_crc_check( eeprom_coeff, (eeprom_coeff[MS5837_CRC_INDEX] & 0xF000)>>12 ) )
		return ms5837_status_crc_error;
	
	ms5837_coeff_read = true;
	
	return ms5837_status_ok;
}

/**
 * \brief Triggers conversion and read ADC value
 *
 * \param[in] uint8_t : Command used for conversion (will determine Temperature vs Pressure and osr)
 * \param[out] uint32_t* : ADC value.
 *
 * \return ms5837_status : status of MS5837
 *       - ms5837_status_ok : I2C transfer completed successfully
 *       - ms5837_status_i2c_transfer_error : Problem with i2c transfer
 *       - ms5837_status_no_i2c_acknowledge : I2C did not acknowledge
 */
static enum ms5837_status ms5837_conversion_and_read_adc(uint8_t cmd, uint32_t *adc)
{
	enum ms5837_status status;
	enum status_code i2c_status;
	uint8_t buffer[3];
	
	buffer[0] = 0;
	buffer[1] = 0;
	buffer[2] = 0;

	/* Read data */
    struct i2c_master_packet read_transfer = {
		.address     = MS5837_ADDR,
		.data_length = 3,
		.data        = buffer,
	};

	status = ms5837_write_command(cmd);
	// delay conversion depending on resolution
	delay_ms( conversion_time[ (cmd & MS5837_CONVERSION_OSR_MASK)/2 ]/1000 );
	if( status != ms5837_status_ok)
		return status;

	// Send the read command
	status = ms5837_write_command(MS5837_READ_ADC);
	if( status != ms5837_status_ok)
		return status;
	
    i2c_status = i2c_master_read_packet_wait(&read_transfer);
	if( i2c_status == STATUS_ERR_OVERFLOW )
		return ms5837_status_no_i2c_acknowledge;
	if( i2c_status != STATUS_OK)
		return ms5837_status_i2c_transfer_error;

	*adc = ((uint32_t)buffer[0] << 16) | ((uint32_t)buffer[1] << 8) | buffer[2];
	
	return status;
}

/**
 * \brief Reads the temperature and pressure ADC value and compute the compensated values.
 *
 * \param[out] float* : Celsius Degree temperature value
 * \param[out] float* : mbar pressure value
 *
 * \return ms5837_status : status of MS5837
 *       - ms5837_status_ok : I2C transfer completed successfully
 *       - ms5837_status_i2c_transfer_error : Problem with i2c transfer
 *       - ms5837_status_no_i2c_acknowledge : I2C did not acknowledge
 *       - ms5837_status_crc_error : CRC check error on the coefficients
 */
enum ms5837_status ms5837_read_temperature_and_pressure( float *temperature, float *pressure)
{
	enum ms5837_status status = ms5837_status_ok;
	uint32_t adc_temperature, adc_pressure;
	int32_t dT, TEMP;
	int64_t OFF, SENS, P, T2, OFF2, SENS2;
	uint8_t cmd;
	
	// If first time adc is requested, get EEPROM coefficients
	if( ms5837_coeff_read == false )
		status = ms5837_read_eeprom();
	if( status != ms5837_status_ok)
		return status;
	
	// First read temperature
	cmd = ms5837_resolution_osr*2;
	cmd |= MS5837_START_TEMPERATURE_ADC_CONVERSION;
	status = ms5837_conversion_and_read_adc( cmd, &adc_temperature);
	if( status != ms5837_status_ok)
		return status;

	// Now read pressure
	cmd = ms5837_resolution_osr*2;
	cmd |= MS5837_START_PRESSURE_ADC_CONVERSION;
	status = ms5837_conversion_and_read_adc( cmd, &adc_pressure);
	if( status != ms5837_status_ok)
		return status;
    
    if (adc_temperature == 0 || adc_pressure == 0)
        return ms5837_status_i2c_transfer_error;

	// Difference between actual and reference temperature = D2 - Tref
	dT = (int32_t)adc_temperature - ((int32_t)eeprom_coeff[MS5837_REFERENCE_TEMPERATURE_INDEX] << 8);
	
	// Actual temperature = 2000 + dT * TEMPSENS
	TEMP = 2000 + ((int64_t)dT * (int64_t)eeprom_coeff[MS5837_TEMP_COEFF_OF_TEMPERATURE_INDEX] >> 23) ;
	
	// Second order temperature compensation
	if( TEMP < 2000 )
	{
		T2 = ( 3 * ( (int64_t)dT  * (int64_t)dT  ) ) >> 33;
		OFF2 = 3 * ((int64_t)TEMP - 2000) * ((int64_t)TEMP - 2000) / 2 ;
		SENS2 = 5 * ((int64_t)TEMP - 2000) * ((int64_t)TEMP - 2000) / 8 ;
		
		if( TEMP < -1500 )
		{
			OFF2 += 7 * ((int64_t)TEMP + 1500) * ((int64_t)TEMP + 1500) ;
			SENS2 += 4 * ((int64_t)TEMP + 1500) * ((int64_t)TEMP + 1500) ;
		}
	}
	else
	{
		T2 = ( 2 * ( (int64_t)dT  * (int64_t)dT  ) ) >> 37;
		OFF2 = ((int64_t)TEMP + 1500) * ((int64_t)TEMP + 1500) >> 4;
		SENS2 = 0 ;
	}
	
	// OFF = OFF_T1 + TCO * dT
	OFF = ( (int64_t)(eeprom_coeff[MS5837_PRESSURE_OFFSET_INDEX]) << 16 ) + ( ( (int64_t)(eeprom_coeff[MS5837_TEMP_COEFF_OF_PRESSURE_OFFSET_INDEX]) * dT ) >> 7 ) ;
	OFF -= OFF2 ;
	
	// Sensitivity at actual temperature = SENS_T1 + TCS * dT
	SENS = ( (int64_t)eeprom_coeff[MS5837_PRESSURE_SENSITIVITY_INDEX] << 15 ) + ( ((int64_t)eeprom_coeff[MS5837_TEMP_COEFF_OF_PRESSURE_SENSITIVITY_INDEX] * dT) >> 8 ) ;
	SENS -= SENS2 ;
	
	// Temperature compensated pressure = D1 * SENS - OFF
	P = ( ( (adc_pressure * SENS) >> 21 ) - OFF ) >> 13 ;
	
	*temperature = ( (float)TEMP - T2 ) / 100;
	*pressure = (float)P / 100;
	
	return status;
}

/**
 * \brief CRC check
 *
 * \param[in] uint16_t *: List of EEPROM coefficients
 * \param[in] uint8_t : crc to compare with
 *
 * \return bool : TRUE if CRC is OK, FALSE if KO
 */
bool ms5837_crc_check (uint16_t *n_prom, uint8_t crc)
{
	uint8_t cnt, n_bit;
	uint16_t n_rem, crc_read;
	
	n_rem = 0x00;
	crc_read = n_prom[0];
	n_prom[MS5837_COEFFICIENT_NUMBERS] = 0;
	n_prom[0] = (0x0FFF & (n_prom[0]));    // Clear the CRC byte

	for( cnt = 0 ; cnt < (MS5837_COEFFICIENT_NUMBERS+1)*2 ; cnt++ ) {

		// Get next byte
		if (cnt%2 == 1)
			n_rem ^=  n_prom[cnt>>1] & 0x00FF ;
		else
			n_rem ^=  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 <<= 1;
		}
	}
	n_rem >>= 12;
	n_prom[0] = crc_read;
	
	return  ( n_rem == crc );
}

#ifdef __cplusplus
}
#endif