sht21.c File Reference

#include <compiler.h>
#include <cfg/os.h>
#include <sys/heap.h>
#include <sys/timer.h>
#include <sys/event.h>
#include <dev/twif.h>
#include <cfg/sht21.h>
#include <dev/sht21.h>

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Defines
#define	SHT_READ_COUNT   3
#define	POLYNOMIAL   0x131
#define	T1x100   -4685L
#define	T2x100   17572L
#define	H1x100   -600L
#define	H2x100   12500L
#define	SHT_POLL_TOUT   90
#define	SHT_POLL_CYCLE   5
#define	SHT21_PRECISION   SHT_RES_12_14
Functions
int	ShtCrc (uint8_t *Data, uint8_t Size)
	Calculate 8-Bit checksum with given polynomial.
int	ShtCommand (uint8_t cmd, uint16_t *data)
	Read data from sensor device.
int	ShtRead (uint8_t cmd, int16_t *val)
	Return real sensor value.
int	ShtInit (void)
	Register and initialize SHT2x sensor device.
Variables
HANDLE	sht_mutex

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Define Documentation

#define SHT_READ_COUNT   3

Referenced by ShtCommand().

#define POLYNOMIAL   0x131

Referenced by ShtCrc().

#define T1x100   -4685L

Referenced by ShtRead().

#define T2x100   17572L

Referenced by ShtRead().

#define H1x100   -600L

Referenced by ShtRead().

#define H2x100   12500L

Referenced by ShtRead().

#define SHT_POLL_TOUT   90

Referenced by ShtCommand().

#define SHT_POLL_CYCLE   5

Referenced by ShtCommand().

#define SHT21_PRECISION   SHT_RES_12_14

Referenced by ShtInit().

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Function Documentation

int ShtCrc	(	uint8_t *	Data,
		uint8_t	Size
	)

Calculate 8-Bit checksum with given polynomial.

This function calculates the checksum of a sensirion device returned data and validates it against the last byte transmitted. P(x) = x^8 + x^5 + x^4 + 1 = 100110001

Data Pointer to data to be checked. Size Size of data.

Returns:

-1 if CRC failed else 0

References POLYNOMIAL.

Referenced by ShtCommand().

int ShtCommand	(	uint8_t	cmd,
		uint16_t *	data
	)

Read data from sensor device.

This function reads the raw value of a SHT2x sensor device. To get the real sensor value, the formulas given by the datasheet have to be applied to this raw value.

Parameters:

cmd	can be SHT_GET_HUM or SHT_GET_TMP.
data	Pointer to data value.

Returns:

-1 read failed else 0.

References I2C_SLA_SHT21, NULL, NutEventPost(), NutEventWait(), NutSleep(), rc, SHT_GET_HUM, SHT_GET_TEMP, SHT_GET_USER, sht_mutex, SHT_POLL_CYCLE, SHT_POLL_TOUT, SHT_READ_COUNT, SHT_SET_USER, SHT_SOFT_RESET, ShtCrc(), TwMasterRegRead, and TwMasterTransact.

Referenced by ShtInit(), and ShtRead().

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int ShtRead	(	uint8_t	cmd,
		int16_t *	val
	)

Return real sensor value.

This function returns either the temperature or the humidity value to a supplied int16_t pointer. The value is decimal with 2 decimal digits: val=2604 -> 26.04°C val=2335 -> 23.35rH

Parameters:

cmd	Either SHT_GET_TEMP or SHT_GET_HUM.
val	Pointer to store the value to.

Returns:

-1 if failed else 0.

References H1x100, H2x100, rc, SHT_GET_HUM, SHT_GET_TEMP, ShtCommand(), T1x100, and T2x100.

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int ShtInit

(

void

)

Register and initialize SHT2x sensor device.

This function initializes the structures and I2C bus for use with SHT2x sensor device. It checks communication too.

Returns:

-1 if init failed else 0.

References NutEventPost(), rc, SHT21_PRECISION, SHT_GET_USER, sht_mutex, SHT_RES_MASK, SHT_SET_USER, SHT_SOFT_RESET, and ShtCommand().

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Variable Documentation

HANDLE sht_mutex

Referenced by ShtCommand(), and ShtInit().