/*********************************************************************************
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* Copyright: (C) 2024 LingYun IoT System Studio
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* All rights reserved.
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*
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* Filename: sht20_fops.c
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* Description: This file is temperature and relative humidity sensor SHT20 code
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*
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* Version: 1.0.0(2024/05/08)
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* Author: Guo Wenxue <guowenxue@gmail.com>
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* ChangeLog: 1, Release initial version on "2024/05/08 12:13:26"
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*
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* Pin connection:
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*
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* SHT20 Module IGKBoard
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* VCC <-----> 3.3V
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* SDA <-----> #Pin3(I2C1_SDA)
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* SCL <-----> #Pin5(I2C1_SCL)
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* GND <-----> GND
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*
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* /run/media/mmcblk1p1/config.txt:
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*
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* # Eanble I2C overlay
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* dtoverlay_i2c=1
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**
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********************************************************************************/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdint.h>
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#include <string.h>
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#include <unistd.h>
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#include <time.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <sys/ioctl.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <linux/types.h>
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#include <linux/i2c.h>
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#include <linux/i2c-dev.h>
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int sht20_checksum(uint8_t *data, int len, int8_t checksum);
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static inline void msleep(unsigned long ms);
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static inline void dump_buf(const char *prompt, uint8_t *buf, int size);
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int main(int argc, char **argv)
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{
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int fd, rv;
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float temp, rh;
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char *i2c_dev = NULL;
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uint8_t buf[4];
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if( argc != 2)
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{
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printf("This program used to do I2C test by SHT20 sensor.\n");
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printf("Usage: %s /dev/i2c-x\n", argv[0]);
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return 0;
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}
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i2c_dev = argv[1];
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/*+--------------------------------+
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*| open /dev/i2c-x device |
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*+--------------------------------+*/
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if( (fd=open(i2c_dev, O_RDWR)) < 0)
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{
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printf("i2c device open failed: %s\n", strerror(errno));
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return -1;
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}
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/*+--------------------------------+
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*| set I2C mode and slave address |
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*+--------------------------------+*/
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ioctl(fd, I2C_TENBIT, 0); /* Not 10-bit but 7-bit mode */
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ioctl(fd, I2C_SLAVE, 0x40); /* set SHT2x slava address 0x40 */
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/*+--------------------------------+
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*| software reset SHT20 sensor |
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*+--------------------------------+*/
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buf[0] = 0xFE;
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write(fd, buf, 1);
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msleep(50);
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/*+--------------------------------+
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*| trigger temperature measure |
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*+--------------------------------+*/
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buf[0] = 0xF3;
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write(fd, buf, 1);
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msleep(85); /* datasheet: typ=66, max=85 */
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memset(buf, 0, sizeof(buf));
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read(fd, buf, 3);
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dump_buf("Temperature sample data: ", buf, 3);
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if( !sht20_checksum(buf, 2, buf[2]) )
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{
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printf("Temperature sample data CRC checksum failure.\n");
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goto cleanup;
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}
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temp = 175.72 * (((((int) buf[0]) << 8) + buf[1]) / 65536.0) - 46.85;
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/*+--------------------------------+
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*| trigger humidity measure |
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*+--------------------------------+*/
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buf[0] = 0xF5;
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write(fd, buf, 1);
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msleep(29); /* datasheet: typ=22, max=29 */
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memset(buf, 0, sizeof(buf));
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read(fd, buf, 3);
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dump_buf("Relative humidity sample data: ", buf, 3);
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if( !sht20_checksum(buf, 2, buf[2]) )
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{
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printf("Relative humidity sample data CRC checksum failure.\n");
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goto cleanup;
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}
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rh = 125 * (((((int) buf[0]) << 8) + buf[1]) / 65536.0) - 6;
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/*+--------------------------------+
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*| print the measure result |
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*+--------------------------------+*/
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printf("Temperature=%lf 'C relative humidity=%lf%%\n", temp, rh);
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cleanup:
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close(fd);
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return 0;
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}
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int sht20_checksum(uint8_t *data, int len, int8_t checksum)
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{
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int8_t crc = 0;
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int8_t bit;
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int8_t byteCtr;
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//calculates 8-Bit checksum with given polynomial: x^8 + x^5 + x^4 + 1
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for (byteCtr = 0; byteCtr < len; ++byteCtr)
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{
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crc ^= (data[byteCtr]);
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for ( bit = 8; bit > 0; --bit)
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{
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/* x^8 + x^5 + x^4 + 1 = 0001 0011 0001 = 0x131 */
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if (crc & 0x80) crc = (crc << 1) ^ 0x131;
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else crc = (crc << 1);
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}
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}
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if (crc != checksum)
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return 0;
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else
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return 1;
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}
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static inline void msleep(unsigned long ms)
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{
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struct timespec cSleep;
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unsigned long ulTmp;
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cSleep.tv_sec = ms / 1000;
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if (cSleep.tv_sec == 0)
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{
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ulTmp = ms * 10000;
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cSleep.tv_nsec = ulTmp * 100;
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}
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else
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{
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cSleep.tv_nsec = 0;
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}
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nanosleep(&cSleep, 0);
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return ;
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}
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static inline void dump_buf(const char *prompt, uint8_t *buf, int size)
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{
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int i;
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if( !buf )
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{
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return ;
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}
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if( prompt )
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{
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printf("%-32s ", prompt);
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}
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for(i=0; i<size; i++)
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{
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printf("%02x ", buf[i]);
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}
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printf("\n");
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return ;
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}
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