si7021.c

// Copyright (c) Konstantin Belyalov. All rights reserved.
// Licensed under the MIT license.

#include "si7021.h"


#define SI7021_ADDRESS_READ          (0x40 << 1) | 0x01
#define SI7021_ADDRESS_WRITE         (0x40 << 1)

#define SI7021_MEASURE_HOLD           0xE5 // Measure Relative Humidity, Hold Master Mode
#define SI7021_MEASURE_NOHOLD         0xF5 // Measure Relative Humidity, No Hold Master Mode
#define SI7021_MEASURE_TEMP_HOLD      0xE3 // Measure Temperature, Hold Master Mode
#define SI7021_MEASURE_TEMP_NOHOLD    0xF3 // Measure Temperature, No Hold Master Mode
#define SI7021_READ_PREV_TEMP         0xE0 // Read Temperature Value from Previous RH Measurement
#define SI7021_RESET                  0xFE
#define SI7021_WRITE_USER_REG1        0xE6 // Write RH/T User Register 1
#define SI7021_READ_USER_REG1         0xE7 // Read RH/T User Register 1
#define SI7021_WRITE_HEATER_REG       0x51 // Write Heater Control Register
#define SI7021_READ_HEATER_REG        0x11 // Read Heater Control Register
#define SI7021_READ_ID1               0xFA0F // Read Electronic ID 1st Byte
#define SI7021_READ_ID2               0xFCC9 // Read Electronic ID 2nd Byte
#define SI7021_FIRMWARE_VERSION       0x84B8 // Read Firmware Revision

// Helper to read 2 bytes of device ID
static uint32_t _read_id(I2C_HandleTypeDef *hi2c, uint32_t reg)
{
  uint32_t id = 0;
  uint8_t si7021_buf[4];

  si7021_buf[0] = reg >> 8;
  si7021_buf[1] = reg & 0xff;

  int res = HAL_I2C_Master_Transmit(hi2c, SI7021_ADDRESS_WRITE, &si7021_buf[0], 2, 100);
  if (res != HAL_OK) {
    goto out;
  }
  res = HAL_I2C_Master_Receive(hi2c, SI7021_ADDRESS_READ, &si7021_buf[0], 4, 100);
  if (res != HAL_OK) {
    goto out;
  }

  id = si7021_buf[0] << 24;
  id |= si7021_buf[1] << 16;
  id |= si7021_buf[2] << 8;
  id |= si7021_buf[3];

out:
  return id;
}

// Helper to read and convert temperature into uint format
static int32_t _read_and_convert_temperature(I2C_HandleTypeDef *hi2c)
{
  uint8_t si7021_buf[4];
  int res = HAL_I2C_Master_Receive(hi2c, SI7021_ADDRESS_READ, si7021_buf, 2, 100);

  if (res != HAL_OK) {
    return SI7021_MEASURE_FAILED;
  }

  int64_t temp_code = (si7021_buf[0] << 8 | si7021_buf[1]) * 100;
  int64_t temp = 17572 * temp_code / 6553500 - 4685;

  if (temp > 12500 || temp < -4000) {
    return SI7021_MEASURE_FAILED;
  }

  return (int32_t)temp;
}

uint64_t si7021_read_id(I2C_HandleTypeDef *hi2c)
{
  uint32_t id1 = _read_id(hi2c, SI7021_READ_ID1);
  uint32_t id2 = _read_id(hi2c, SI7021_READ_ID2);

  if (id1 == 0 || id2 == 0) {
    return 0;
  }

  return (uint64_t)id1 << 32 | id2;
}

uint32_t si7021_set_config(I2C_HandleTypeDef *hi2c, uint8_t heater, uint8_t resolution)
{
  uint8_t si7021_buf[4];
  si7021_buf[0] = SI7021_WRITE_USER_REG1;
  si7021_buf[1] = heater | resolution;

  return HAL_I2C_Master_Transmit(hi2c, SI7021_ADDRESS_WRITE, &si7021_buf[0], 2, 100);
}

uint32_t si7021_set_heater_power(I2C_HandleTypeDef *hi2c, uint8_t power)
{
  uint8_t si7021_buf[4];
  si7021_buf[0] = SI7021_WRITE_HEATER_REG;
  si7021_buf[1] = power;

  return HAL_I2C_Master_Transmit(hi2c, SI7021_ADDRESS_WRITE, si7021_buf, 2, 100);
}

uint32_t si7021_measure_humidity(I2C_HandleTypeDef *hi2c)
{
  uint8_t si7021_buf[4];
  si7021_buf[0] = SI7021_MEASURE_NOHOLD;

  // Start measure
  int res = HAL_I2C_Master_Transmit(hi2c, SI7021_ADDRESS_WRITE, si7021_buf, 1, 100);
  if (res != HAL_OK) {
    return SI7021_MEASURE_FAILED;
  }
  HAL_Delay(30);

  // Read result
  res = HAL_I2C_Master_Receive(hi2c, SI7021_ADDRESS_READ, si7021_buf, 2, 100);
  if (res != HAL_OK) {
    return SI7021_MEASURE_FAILED;
  }

  return (si7021_buf[0] << 8 | si7021_buf[1]) * 125 / 65536 - 6;
}

int32_t si7021_measure_temperature(I2C_HandleTypeDef *hi2c)
{
  uint8_t si7021_buf[4];
  si7021_buf[0] = SI7021_MEASURE_TEMP_NOHOLD;

  int res = HAL_I2C_Master_Transmit(hi2c, SI7021_ADDRESS_WRITE, &si7021_buf[0], 1, 100);
  if (res != HAL_OK) {
    return SI7021_MEASURE_FAILED;
  }
  HAL_Delay(30);

  return _read_and_convert_temperature(hi2c);
}

int32_t si7021_read_previous_temperature(I2C_HandleTypeDef *hi2c)
{
  uint8_t si7021_buf[4];
  si7021_buf[0] = SI7021_READ_PREV_TEMP;

  int res = HAL_I2C_Master_Transmit(hi2c, SI7021_ADDRESS_WRITE, &si7021_buf[0], 1, 100);
  if (res != HAL_OK) {
    return SI7021_MEASURE_FAILED;
  }

  return _read_and_convert_temperature(hi2c);
}