view Small_CPU/Src/pressure.c @ 595:fd0b60dee6f3

Bugfix Selection of primary view: At the begin of the dive and while switching between T7 <=> T3 view a primary view could be shown which was deactivated by the selection dialog. In case the primary view is now deactivated, the next activated view will be shown instead
author Ideenmodellierer
date Mon, 04 Jan 2021 21:32:39 +0100
parents 4644891d2f51
children 8c92f7743e14
line wrap: on
line source

/**
  ******************************************************************************
  * @file    pressure.c 
  * @author  heinrichs weikamp gmbh
  * @date    2014
  * @version V0.0.2
  * @since   20-Oct-2016
  * @brief   
  *           
  @verbatim                 
  ============================================================================== 
                        ##### How to use #####
  ============================================================================== 
	V0.0.2		18-Oct-2016		pressure_calculation_AN520_004_mod_MS5803_30BA__09_2015
	
	@endverbatim
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; COPYRIGHT(c) 2016 heinrichs weikamp</center></h2>
  *
  ******************************************************************************
  */ 



/* surface time
 the last 30 minutes will be saved once per minute in a endless loop
 at the beginning of a dive the oldest value will be used
*/
#include "math.h"
#include "scheduler.h"
#include "pressure.h"
#include "i2c.h"
#include "rtc.h"

#define CMD_RESET 0x1E // ADC reset command
#define CMD_ADC_READ 0x00 // ADC read command
#define CMD_ADC_CONV 0x40 // ADC conversion command
#define CMD_ADC_D1 0x00 // ADC D1 conversion
#define CMD_ADC_D2 0x10 // ADC D2 conversion
#define CMD_ADC_256 0x00 // ADC OSR=256
#define CMD_ADC_512 0x02 // ADC OSR=512
#define CMD_ADC_1024 0x04 // ADC OSR=1024
#define CMD_ADC_2048 0x06 // ADC OSR=2056
#define CMD_ADC_4096 0x08 // ADC OSR=4096
#define CMD_PROM_RD 0xA0 // Prom read command

/* remove comment to use a predefined profile for pressure changes instead of real world data */
/* #define SIMULATE_PRESSURE */

#define PRESSURE_SURFACE_MAX_MBAR			(1060.0f)		/* It is unlikely that pressure at surface is greater than this value => clip to it */

#define PRESSURE_SURFACE_QUE					(30u)			/* history buffer [minutes] for past pressure measurements */
#define PRESSURE_SURFACE_EVA_WINDOW				(15u)			/* Number of entries evaluated during instability test. Used to avoid detection while dive enters water */
#define PRESSURE_SURFACE_STABLE_LIMIT			(10u)			/* Define pressure as stable if delta (mBar) is below this value */
#define PRESSURE_SURFACE_DETECT_STABLE_CNT		(5u)			/* Event count to detect stable condition */
#define PRESSURE_SURFACE_UNSTABLE_LIMIT			(50u)			/* Define pressure as not stable if delta (mBar) is larger than this value */
#define PRESSURE_SURFACE_DETECT_UNSTABLE_CNT	(3u)			/* Event count to detect unstable condition */


static uint8_t PRESSURE_ADDRESS = DEVICE_PRESSURE_MS5803;					/* Default Address */

static uint16_t get_ci_by_coef_num(uint8_t coef_num);
//void pressure_calculation_new(void);
//void pressure_calculation_old(void);
static void pressure_calculation_AN520_004_mod_MS5803_30BA__09_2015(void);
//static uint8_t crc4(uint16_t n_prom[]);

static HAL_StatusTypeDef pressure_sensor_get_data(void);
static uint32_t get_adc(void);
uint8_t pressureSensorInitSuccess = 0;

static uint16_t C[8] = { 1 };
static uint32_t D1 = 1;
static uint32_t D2 = 1;
//static uint8_t n_crc;

/*
short C2plus10000 = -1;
short C3plus200 = -1;
short C4minus250 = -1;
short UT1 = -1;
short C6plus100 = -1;
*/
static float pressure_offset = 0.0;		/* Offset value which may be specified by the user via PC Software */
static float temperature_offset = 0.0;	/* Offset value which may be specified by the user via PC Software */

static float ambient_temperature = 0;
static float ambient_pressure_mbar = 1000.0;
static float surface_pressure_mbar = 1000.0;
static float surface_ring_mbar[PRESSURE_SURFACE_QUE] = { 0 };

static uint8_t surface_pressure_writeIndex = 0;
static float surface_pressure_stable_value = 0;
static uint8_t surface_pressure_stable = 0;

static uint8_t secondCounterSurfaceRing = 0;
static uint8_t avgCount = 0;
static float runningAvg = 0;

float get_temperature(void)
{
	return ambient_temperature;
}

float get_pressure_mbar(void)
{
	return ambient_pressure_mbar;
}

float get_surface_mbar(void)
{
	return surface_pressure_mbar;
}


void init_surface_ring(uint8_t force)
{
	if((surface_ring_mbar[0] == 0) || (force))		/* only initialize once. Keep value in place in case of an i2c recovery */
	{
		secondCounterSurfaceRing = 0;				/* restart calculation */
		avgCount = 0;
		runningAvg = 0;

		for(int i=0; i<PRESSURE_SURFACE_QUE; i++)
			surface_ring_mbar[i] = ambient_pressure_mbar;
		surface_pressure_mbar = ambient_pressure_mbar;
		surface_pressure_writeIndex = 0;			/* index of the oldest value in the ring buffer */
	}
}

uint8_t is_surface_pressure_stable(void)
{
	return surface_pressure_stable;
}

float set_last_surface_pressure_stable(void)
{
	surface_pressure_mbar = surface_pressure_stable_value;
	return surface_pressure_stable_value;
}

/* iterate backward through the history memory and evaluate the changes pressure changes during the last 30 minutes */
void evaluate_surface_pressure()
{
	uint8_t index;
	float lastvalue;
	uint8_t stablecnt = 0;
	uint8_t unstablecnt = 0;
	uint8_t EvaluationWindow = PRESSURE_SURFACE_QUE - PRESSURE_SURFACE_EVA_WINDOW;	/* do not use the latest 15 values to avoid unstable condition due to something like fin handling */
	uint8_t EvaluatedValues = 0;

	lastvalue = surface_ring_mbar[surface_pressure_writeIndex];
	surface_pressure_stable_value = surface_ring_mbar[surface_pressure_writeIndex]; /* default: if no stable value is found return the oldest value */
	index = surface_pressure_writeIndex;
	surface_pressure_stable = 1;

	if(index == 0)
	{
		index = PRESSURE_SURFACE_QUE - 1;
	}
	else
	{
		index = index - 1;
	}
	do
	{
		if((EvaluatedValues < EvaluationWindow) &&
			(fabs(surface_pressure_stable_value - surface_ring_mbar[index]) > PRESSURE_SURFACE_UNSTABLE_LIMIT)) /* unusual change during last 30 minutes */
		{
			unstablecnt++;
			if(unstablecnt > PRESSURE_SURFACE_DETECT_UNSTABLE_CNT)
			{
				surface_pressure_stable = 0;
			}
		}
	/* search for a value which does not change for several iterations */
		if (fabs(lastvalue - surface_ring_mbar[index]) < PRESSURE_SURFACE_STABLE_LIMIT)
		{
			stablecnt++;
		}
		else
		{
			stablecnt = 0;
		}
		if ((stablecnt >= PRESSURE_SURFACE_DETECT_STABLE_CNT) && (surface_pressure_stable == 0)&&(surface_pressure_stable_value == surface_ring_mbar[surface_pressure_writeIndex])) /* pressure is unstable => search for new stable value */
		{
			surface_pressure_stable_value = surface_ring_mbar[index];
			unstablecnt = 0;
		}

		lastvalue = surface_ring_mbar[index];

		if(index == 0)
		{
			index = PRESSURE_SURFACE_QUE - 1;
		}
		else
		{
			index = index - 1;
		}
		EvaluatedValues++;
	} while (index != surface_pressure_writeIndex);
}
void update_surface_pressure(uint8_t call_rhythm_seconds)
{
	if(is_init_pressure_done())
	{
		runningAvg = (runningAvg * avgCount + ambient_pressure_mbar) / (avgCount +1);
		avgCount++;
		secondCounterSurfaceRing += call_rhythm_seconds;

		if(secondCounterSurfaceRing >= 60)
		{
			if(runningAvg < PRESSURE_SURFACE_MAX_MBAR)
			{
				surface_ring_mbar[surface_pressure_writeIndex] = runningAvg;
			}
			else
			{
				surface_ring_mbar[surface_pressure_writeIndex] =	PRESSURE_SURFACE_MAX_MBAR;
			}
			surface_pressure_writeIndex++; /* the write index is now pointing to the oldest value in the buffer which will be overwritten next time */

			if(surface_pressure_writeIndex == PRESSURE_SURFACE_QUE)
			{
				surface_pressure_writeIndex = 0;
			}

			surface_pressure_mbar = surface_ring_mbar[surface_pressure_writeIndex]; /* 30 minutes old measurement */

			secondCounterSurfaceRing = 0;
			avgCount = 1;	/* use the current value as starting point but restart the weight decrement of the measurements */
		}
		evaluate_surface_pressure();
	}
}

#ifdef DEMOMODE
float demo_modify_temperature_helper(float bottom_mbar_diff_to_surface)
{
	const float temperature_surface = 31.0;
	const float temperature_bottom = 14.0;

	const float temperature_difference = temperature_bottom - temperature_surface;
	
	// range 0.0 - 1.0
	float position_now = (ambient_pressure_mbar - surface_pressure_mbar) / bottom_mbar_diff_to_surface; 

	if(position_now <= 0)
		return temperature_surface;
	
	if(position_now >= 1)
		return temperature_bottom;

	return temperature_surface + (temperature_difference * position_now);
}


uint32_t demo_modify_temperature_and_pressure(int32_t divetime_in_seconds, uint8_t subseconds, float ceiling_mbar)
{
	
	const float descent_rate = 4000/60;
	const float ascent_rate = 1000/60;
	const uint32_t seconds_descend = (1 * 60) + 30;
	const uint32_t turbo_seconds_at_bottom_start = (0 * 60) + 0;
	const uint32_t seconds_descend_and_bottomtime = seconds_descend + turbo_seconds_at_bottom_start + (2 * 60) + 0;
	uint32_t time_elapsed_in_seconds;
	static float ambient_pressure_mbar_memory = 0;
	static uint32_t time_last_call = 0;
	
	if(divetime_in_seconds <= seconds_descend)
	{
		ambient_pressure_mbar = (divetime_in_seconds * descent_rate) + ((float)(subseconds) * descent_rate) + surface_pressure_mbar;
		ambient_temperature = demo_modify_temperature_helper(descent_rate * seconds_descend);

		time_last_call = divetime_in_seconds;
		return 0;
	}
	else
	if(divetime_in_seconds <= seconds_descend + turbo_seconds_at_bottom_start)
	{
		ambient_pressure_mbar = (seconds_descend * descent_rate) + surface_pressure_mbar;
		ambient_temperature = demo_modify_temperature_helper(descent_rate * seconds_descend);
		ambient_pressure_mbar_memory = ambient_pressure_mbar;
		time_last_call = divetime_in_seconds;
		return turbo_seconds_at_bottom_start;
	}
	else
	if(divetime_in_seconds <= seconds_descend_and_bottomtime)
	{
		ambient_pressure_mbar = (seconds_descend * descent_rate) + surface_pressure_mbar;
		ambient_temperature = demo_modify_temperature_helper(descent_rate * seconds_descend);
		ambient_pressure_mbar_memory = ambient_pressure_mbar;
		time_last_call = divetime_in_seconds;
		return 0;
	}
	else
	{
		time_elapsed_in_seconds = divetime_in_seconds - time_last_call;
		ambient_pressure_mbar = ambient_pressure_mbar_memory - time_elapsed_in_seconds * ascent_rate;

		if(ambient_pressure_mbar < surface_pressure_mbar)
			ambient_pressure_mbar = surface_pressure_mbar;
		else if(ambient_pressure_mbar < ceiling_mbar)
			ambient_pressure_mbar = ceiling_mbar;
		
		ambient_temperature = demo_modify_temperature_helper(descent_rate * seconds_descend);
		ambient_pressure_mbar_memory = ambient_pressure_mbar;
		time_last_call = divetime_in_seconds;
		return 0;
	}
}
#endif

uint8_t is_init_pressure_done(void)
{
	return pressureSensorInitSuccess;
}

uint8_t init_pressure(void)
{
	uint8_t buffer[1];
	buffer[0] = 0x1E;			// Reset Command
	uint8_t retValue = 0xFF;
	
	pressureSensorInitSuccess = false;

/* Probe new sensor first */
	retValue = I2C_Master_Transmit(  DEVICE_PRESSURE_MS5837, buffer, 1);
	if(retValue != HAL_OK)
	{
		PRESSURE_ADDRESS = DEVICE_PRESSURE_MS5803;			// use old sensor
		HAL_Delay(100);
		I2C_DeInit();
		HAL_Delay(100);
		MX_I2C1_Init();
		HAL_Delay(100);
	}
	else
	{
		PRESSURE_ADDRESS = DEVICE_PRESSURE_MS5837;			// Success, use new sensor
	}
	HAL_Delay(3);		//2.8ms according to datasheet

	buffer[0] = 0x1E;			// Reset Command
	retValue = 0xFF;

/* Send reset request to pressure sensor */
	retValue = I2C_Master_Transmit(  PRESSURE_ADDRESS, buffer, 1);
	if(retValue != HAL_OK)
	{
		return (HAL_StatusTypeDef)retValue;
	}
	HAL_Delay(3);		//2.8ms according to datasheet
	
	for(uint8_t i=0;i<7;i++)
	{
		C[i] = get_ci_by_coef_num(i);
	}
	// n_crc = crc4(C); // no evaluation at the moment hw 151026

	if(global.I2C_SystemStatus == HAL_OK)
	{
		pressureSensorInitSuccess = 1;
		retValue = pressure_update();
	}
	return retValue;
}


static uint32_t get_adc(void)
{
	uint8_t buffer[1];
	uint8_t resivebuf[4];
	uint32_t answer = 0xFFFFFFFF;

	buffer[0] = 0x00; // Get ADC
	if(I2C_Master_Transmit( PRESSURE_ADDRESS, buffer, 1) == HAL_OK)
	{
		if(I2C_Master_Receive(  PRESSURE_ADDRESS, resivebuf, 4) == HAL_OK)
		{
			resivebuf[3] = 0;
			answer = 256*256 *(uint32_t)resivebuf[0]  + 256 * (uint32_t)resivebuf[1] + (uint32_t)resivebuf[2];
		}
	}
	return answer;
}


static uint16_t get_ci_by_coef_num(uint8_t coef_num)
{
	uint8_t resivebuf[2];

	uint8_t cmd = CMD_PROM_RD+coef_num*2; 
	I2C_Master_Transmit( PRESSURE_ADDRESS, &cmd, 1);
	I2C_Master_Receive(  PRESSURE_ADDRESS, resivebuf, 2);
	return (256*(uint16_t)resivebuf[0]) + (uint16_t)resivebuf[1];
}



uint8_t pressure_update(void)
{
	HAL_StatusTypeDef statusReturn = HAL_TIMEOUT;
	
	statusReturn = pressure_sensor_get_data();
	pressure_calculation();
	return (uint8_t)statusReturn;
}

/* Switch between pressure and temperature measurement with every successful read operation */
void pressure_update_alternating(void)
{
	static uint8_t getTemperature= 0;

	if(getTemperature)
	{
		if(pressure_sensor_get_temperature_raw() == HAL_OK)
		{
			getTemperature = 0;
		}
	}
	else
	{
		if(pressure_sensor_get_pressure_raw() == HAL_OK)
		{
			getTemperature = 1;
		}
	}
	pressure_calculation();
	return;
}

static uint32_t pressure_sensor_get_one_value(uint8_t cmd, HAL_StatusTypeDef *statusReturn)
{
	uint8_t command = CMD_ADC_CONV + cmd;
	uint32_t adcValue = 0;
	HAL_StatusTypeDef statusReturnTemp = HAL_TIMEOUT;
	
	statusReturnTemp = I2C_Master_Transmit( PRESSURE_ADDRESS, &command, 1);

	if(statusReturn)
	{
		*statusReturn = statusReturnTemp;
	}

	switch (cmd & 0x0f) // wait necessary conversion time
	{
		case CMD_ADC_256 : HAL_Delay(2); break;
		case CMD_ADC_512 : HAL_Delay(4); break;
		case CMD_ADC_1024: HAL_Delay(5); break;
		case CMD_ADC_2048: HAL_Delay(7); break;
		case CMD_ADC_4096: HAL_Delay(11); break;
		default:
			break;
	}
	adcValue = get_adc();
/*	if(adcValue == 0xFFFFFFFF)
	{
		if(statusReturn)
		{
			*statusReturn = HAL_ERROR;
		}
	}*/

	return adcValue;
}


static HAL_StatusTypeDef pressure_sensor_get_data(void)
{
	uint32_t requestedValue = 0;
	HAL_StatusTypeDef statusReturn1 = HAL_TIMEOUT;
	HAL_StatusTypeDef statusReturn2 = HAL_TIMEOUT;
	


	requestedValue = pressure_sensor_get_one_value(CMD_ADC_D2 + CMD_ADC_4096, &statusReturn2);
	if (statusReturn2 == HAL_OK)
	{
		D2 = requestedValue;
	}

	requestedValue = pressure_sensor_get_one_value(CMD_ADC_D1 + CMD_ADC_4096, &statusReturn1);
	if (statusReturn1 == HAL_OK)
	{
		D1 = requestedValue;
	}
	if(statusReturn2 > statusReturn1) // if anything is not HAL_OK (0x00) or worse
		return statusReturn2;
	else
		return statusReturn1;
}


HAL_StatusTypeDef  pressure_sensor_get_pressure_raw(void)
{
	uint32_t requestedValue = 0;
	HAL_StatusTypeDef statusReturn = HAL_TIMEOUT;

	requestedValue = pressure_sensor_get_one_value(CMD_ADC_D1 + CMD_ADC_4096, &statusReturn);
	if (statusReturn == HAL_OK)
	{
		D1 = requestedValue;
	}

	return statusReturn;
}


HAL_StatusTypeDef  pressure_sensor_get_temperature_raw(void)
{
	uint32_t requestedValue = 0;
	HAL_StatusTypeDef statusReturn = HAL_TIMEOUT;

	requestedValue = pressure_sensor_get_one_value(CMD_ADC_D2 + CMD_ADC_4096, &statusReturn);
	if (statusReturn == HAL_OK)
	{
		D2 = requestedValue;
	}
	return statusReturn;
}


#ifdef SIMULATE_PRESSURE
void pressure_simulation()
{
	static uint32_t tickstart = 0;
	static float pressure_sim_mbar = 0;
	static uint32_t passedSecond = 0;
	static uint32_t secondtick = 0;

	uint32_t lasttick = 0;



	if( tickstart == 0)
	{
		tickstart = HAL_GetTick(); /* init time stamp */
		secondtick = tickstart;
		pressure_sim_mbar = 1000;
	}

	lasttick = HAL_GetTick();
	if(time_elapsed_ms(secondtick,lasttick) > 1000) /* one second passed since last tick */
	{
		secondtick = lasttick;
		passedSecond++;

#ifdef DIVE_AFTER_LANDING
		if(passedSecond < 10) pressure_sim_mbar = 1000.0;	 /* stay stable for 10 seconds */
		else if(passedSecond < 300) pressure_sim_mbar -= 1.0; /* decrease pressure in 5 minutes target 770mbar => delta 330 */
		else if(passedSecond < 900) pressure_sim_mbar += 0.0;	/*stay stable 10 minutes*/
		else if(passedSecond < 1500) pressure_sim_mbar += 0.5;	/* return to 1 bar in 10 Minutes*/
		else if(passedSecond < 1800) pressure_sim_mbar += 0.0;	/* 5 minutes break */
		else if(passedSecond < 2000) pressure_sim_mbar += 10.0; /* start dive */
		else if(passedSecond < 2300) pressure_sim_mbar += 0.0;  /* stay on depth */
		else if(passedSecond < 2500) pressure_sim_mbar -= 10.0; /* return to surface */
		else pressure_sim_mbar = 1000.0;					/* final state */
#else	/* short dive */
		if(passedSecond < 10) pressure_sim_mbar = 1000.0;	   /* stay stable for 10 seconds */
		else if(passedSecond < 180) pressure_sim_mbar += 10.0; /* Start dive */
		else if(passedSecond < 300) pressure_sim_mbar += 0.0;	/*stay on depth*/
		else if(passedSecond < 460) pressure_sim_mbar -= 10.0;	/* return to surface */
		else if(passedSecond < 600) pressure_sim_mbar += 0.0;   /* stay */
		else if(passedSecond < 610) pressure_sim_mbar = 1000.0; /* get ready for second dive */
		else if(passedSecond < 780) pressure_sim_mbar += 10.0; /* Start dive */
		else if(passedSecond < 900) pressure_sim_mbar += 0.0;	/*stay on depth*/
		else if(passedSecond < 1060) pressure_sim_mbar -= 10.0;	/* return to surface */
		else if(passedSecond < 1200) pressure_sim_mbar += 0.0;   /* stay */
		else pressure_sim_mbar = 1000.0;					/* final state */
#endif
	}


	ambient_pressure_mbar = pressure_sim_mbar;
	ambient_temperature = 25.0;
	return;
}

#endif

void pressure_calculation(void)
{
	if(global.I2C_SystemStatus != HAL_OK)
		return;

#ifdef SIMULATE_PRESSURE
	pressure_simulation();
#else
	pressure_calculation_AN520_004_mod_MS5803_30BA__09_2015();
#endif
}

static void pressure_calculation_AN520_004_mod_MS5803_30BA__09_2015(void)
{
	static float runningAvg = 0;
	static uint8_t avgCnt = 0;

	uint32_t local_D1; // ADC value of the pressure conversion
	uint32_t local_D2; // ADC value of the temperature conversion
	int32_t local_Px10; // compensated pressure value
	int32_t local_Tx100; // compensated temperature value
	int64_t local_dT; // int32_t, difference between actual and measured temperature
	int64_t local_OFF; // offset at actual temperature
	int64_t local_SENS; // sensitivity at actual temperature

	float calc_pressure;

	int64_t T2;
	int64_t OFF2;
	int64_t SENS2;

	local_D1 = D1;
	local_D2 = D2;

	local_dT 		= ((int64_t)local_D2) - ((int64_t)C[5]) * 256; //pow(2,8);
	local_OFF 	= ((int64_t)C[2]) * 65536 + local_dT * ((int64_t)C[4]) / 128; // pow(2,16), pow(2,7)
	local_SENS 	= ((int64_t)C[1]) * 32768 + local_dT * ((int64_t)C[3]) / 256; // pow(2,15), pow(2,8)

	local_Tx100 = (int32_t)(2000 + (local_dT * ((int64_t)C[6])) / 8388608);// pow(2,23)


	if(local_Tx100 < 2000) // low temperature
	{
		T2  = 3 * local_dT;
		T2 *= local_dT;
		T2 /= 8589934592;

		OFF2 = ((int64_t)local_Tx100) - 2000;
		OFF2 *= OFF2;
		OFF2 *= 3;
		OFF2 /= 2;
		
		SENS2 = ((int64_t)local_Tx100) - 2000;
		SENS2 *= SENS2;
		SENS2 *= 5;
		SENS2 /= 8;

		local_Tx100 -= (int32_t)T2;
		local_OFF 	-= OFF2;
		local_SENS 	-= SENS2;
	}
	else
	{
		T2  = 7 * local_dT;
		T2 *= local_dT;
		T2 /= 137438953472;

		OFF2 = ((int64_t)local_Tx100) - 2000;
		OFF2 *= OFF2;
		OFF2 /= 16;
		
		local_Tx100 -= (int32_t)T2;
		local_OFF 	-= OFF2;
	}
	
	local_Px10 = (int32_t)(
							(((int64_t)((local_D1 * local_SENS) / 2097152)) - local_OFF)
								/  8192 );//     )) / 10; // pow(2,21), pow(2,13)

	ambient_temperature = ((float)local_Tx100) / 100;
	ambient_temperature	+= temperature_offset;

	calc_pressure = ((float)local_Px10) / 10;
	calc_pressure += pressure_offset;

	runningAvg = (avgCnt * runningAvg + calc_pressure) / (avgCnt + 1);
	if (avgCnt < 10)	/* build an average considering the last measurements to have a weight "1 of 10" */
	{					/* Main reason for this is the jitter of up to +-10 HPa in surface mode which is caused */
		avgCnt++;		/* by the measurement range of the sensor which is focused on under water pressure measurement */
	}
	ambient_pressure_mbar = runningAvg;
}


/* taken from AN520 by meas-spec.com dated 9. Aug. 2011
 * short and int are both 16bit according to AVR/GCC google results
 */
/*static uint8_t crc4(uint16_t n_prom[])
{
uint16_t cnt; // simple counter
uint16_t n_rem; // crc reminder
uint16_t crc_read; // original value of the crc
uint8_t n_bit;
n_rem = 0x00;
crc_read=n_prom[7]; //save read CRC
n_prom[7]=(0xFF00 & (n_prom[7])); //CRC byte is replaced by 0
for (cnt = 0; cnt < 16; cnt++) // operation is performed on bytes
{ // choose LSB or MSB
if (cnt%2==1) n_rem ^= (uint16_t) ((n_prom[cnt>>1]) & 0x00FF);
else n_rem ^= (uint16_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);
}
}
}
n_rem= (0x000F & (n_rem >> 12)); // // final 4-bit reminder is CRC code
n_prom[7]=crc_read; // restore the crc_read to its original place
return (n_rem ^ 0x00);
}

void test_calculation(void)
{
	C1 = 29112;
	C2 = 26814;
	C3 = 19125;
	C4 = 17865;
	C5 = 32057;
	C6 = 31305;
	
	C2_x_2p16 = C2 * 65536;
	C1_x_2p15 = C1 * 32768;
	
	D1 = 4944364;
	D2 = 8198974;	
		pressure_calculation() ;
};
*/
void pressure_set_offset (float pressureOffset, float temperatureOffset)
{
	if(pressure_offset != pressureOffset)				/* we received a new value => reinit surface que */
	{
		ambient_pressure_mbar -= pressure_offset;		/* revert old value */
		ambient_pressure_mbar += pressureOffset;		/* apply new offset */
		init_surface_ring(1);
	}

	pressure_offset = pressureOffset;
	temperature_offset = temperatureOffset;
}