si702x.c

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <linux/i2c-dev.h>
#include "si702x.h"

int si702x_begin(const char *device)
{
  int status = 0;
  si702xFd = open(device, O_RDWR);
  if(si702xFd < 0)
    {
      printf("ERROR: si702x open failed\n");
      return -1;
    }
  status = ioctl(si702xFd, I2C_SLAVE, ID_SI7020);
  if(status < 0)
    {
      printf("ERROR: si702x ioctl error\n");
      close(si702xFd);
      return -1;
    }
}

float Si702x_readTemperature(void)
{
  float temp;
  unsigned int rawTemp;
  Si702x_I2C_write8(CMD_MEASURE_TEMPERATURE_HOLD);
  rawTemp = Si702x_I2C_read16(CMD_MEASURE_TEMPERATURE_HOLD);
  temp = (rawTemp * 175.72 / 65536) - 46.85;
  return temp;
}

float Si702x_readHumidity(void)
{
  float humi;
  unsigned int rawHumi;
  Si702x_I2C_write8(CMD_MEASURE_HUMIDITY_HOLD);
  usleep(10000);
  rawHumi = Si702x_I2C_read16(CMD_MEASURE_HUMIDITY_HOLD);
  usleep(10000);
  humi = (rawHumi * 125.0 / 65536) - 6;
  return humi;
}

unsigned short Si702x_I2C_read16(unsigned char reg)
{
  unsigned char rbuf[2];
  write(si702xFd, &reg, 1);
  read(si702xFd, rbuf, 2);
  return (unsigned short)(rbuf[0] << 8 | rbuf[1]);
}

void Si702x_I2C_write8(unsigned char val)
{
  unsigned char wbuf[1];
  wbuf[1] = val;
  write(si702xFd, wbuf, 1);
}