136 lines
3.3 KiB
C
136 lines
3.3 KiB
C
/*
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* sht4x.c
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*
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* Created on: Jun 8, 2021
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* Author: user
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*/
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#include "scd4x.h"
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/*
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* Functions to be implemented by user
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*/
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/* I2C */
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int8_t scd4x_i2c_transmit(uint8_t address, uint8_t *buffer, int len) __attribute__((weak));
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int8_t scd4x_i2c_receive(uint8_t address, uint8_t *buffer, int len) __attribute__((weak));
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/* CRC */
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uint8_t sensirion_crc8_calculate(const uint8_t *data, uint16_t count) __attribute__((weak));
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/* Interrupts */
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int8_t scd4x_disable_interrupts(void) __attribute__((weak));
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int8_t scd4x_enable_interrupts(void) __attribute__((weak));
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/* delay function */
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void delay_ms(int delay_ms) __attribute__((weak));
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/*
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* Public functions
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*/
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int8_t scd4x_send_cmd(scd4x_cmd_t cmd)
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{
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uint8_t buffer[32];
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int result;
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// start measurement
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buffer[0] = cmd >> 8;
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buffer[1] = cmd & 0x00ff;
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scd4x_disable_interrupts();
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result = scd4x_i2c_transmit(SCD4X_I2C_ADDRESS<<1, buffer, 2);
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scd4x_enable_interrupts();
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if (result != 0) {
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return SCD4X_ERROR;
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}
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/* Sensirion sensors return NACK after last byte (so NACK at the end is ok) */
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return SCD4X_OK;
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}
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int8_t scd4x_get_serial(uint8_t serial[6])
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{
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uint8_t buffer[16];
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int result;
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scd4x_send_cmd(SCD4X_GET_SERIAL_NUMBER);
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scd4x_disable_interrupts();
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result = scd4x_i2c_receive(SCD4X_I2C_ADDRESS << 1, buffer, 9);
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scd4x_enable_interrupts();
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if (result != 0) {
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return SCD4X_ERROR;
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}
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return SCD4X_OK;
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}
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int8_t scd4x_read_data(uint8_t *buffer, int len)
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{
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return SCD4X_OK;
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}
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int8_t scd4x_start_periodic_measurement( void )
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{
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return scd4x_send_cmd(SCD4X_START_PERIODIC_MEASUREMENT);
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}
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int8_t scd4x_stop_periodic_measurement( void )
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{
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return scd4x_send_cmd(SCD4X_STOP_PERIODIC_MEASUREMENT);
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}
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int8_t scd4x_perform_factory_reset( void )
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{
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return scd4x_send_cmd(SCD4X_PERFORM_FACTORY_RESET);
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}
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int8_t scd4x_read_measurement(uint16_t *co2, int16_t *temperature, uint16_t *relative_humidity)
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{
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uint8_t buffer[32];
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int result;
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/* start measurement */
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buffer[0] = SCD4X_READ_MEASUREMENT >> 8;
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buffer[1] = SCD4X_READ_MEASUREMENT & 0x00ff;
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/* disable interrupts to prevent MODBUS/I2C conflict */
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scd4x_disable_interrupts();
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result = scd4x_i2c_transmit(SCD4X_I2C_ADDRESS<<1, buffer, 2);
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scd4x_enable_interrupts();
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if (result != 0) {
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return SCD4X_ERROR;
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}
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delay_ms(1);
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/* read out */
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scd4x_disable_interrupts();
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result = scd4x_i2c_receive(SCD4X_I2C_ADDRESS<<1, buffer, 9);
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scd4x_enable_interrupts();
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if (result != 0)
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{
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return SCD4X_ERROR;
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}
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/* Convert to T and RH; taken directly from pseudocode in SHT4x datasheet, page 3 */
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uint32_t co2_ticks = (buffer[0] << 8) + buffer[1];
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uint8_t co2_crc = buffer[2];
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uint32_t t_ticks = (buffer[3] << 8) + buffer[4];
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uint8_t t_crc = buffer[5];
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uint32_t rh_ticks = (buffer[6] << 8) + buffer[7];
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uint8_t rh_crc = buffer[8];
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/* check CRC-8 checksum */
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uint8_t crc_correct = sensirion_crc8_calculate(buffer, 2) == co2_crc;
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crc_correct &= sensirion_crc8_calculate(buffer + 3, 2) == t_crc;
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crc_correct &= sensirion_crc8_calculate(buffer + 6, 2) == rh_crc;
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if (!crc_correct) {
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return SCD4X_CRC8_ERROR;
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}
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/* copy to output variables */
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int t_degC = -450 + 10 * 175 * t_ticks / 65535;
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int rh_pRH = 100 * rh_ticks / 65535;
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if (rh_pRH > 100) {
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rh_pRH = 100;
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}
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if (rh_pRH < 0) {
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rh_pRH = 0;
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}
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*co2 = co2_ticks;
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*temperature = t_degC;
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*relative_humidity = rh_pRH;
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return SCD4X_OK;
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}
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