scd4x/scd4x.c

/*
 * File:        scd4x.h
 * Description: Sensirion SCD4x sensor communication library
 * Author:      David Zaitlik
 * Date:        2022-06-08
 *
 *
 * Copyright (c) 2024 Veles Labs s.r.o.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */

#include "scd4x.h"

/*
 * Functions to be implemented by user
 */

/* I2C */
int8_t scd4x_i2c_transmit(uint8_t address, uint8_t *buffer, int len) __attribute__((weak));
int8_t scd4x_i2c_receive(uint8_t address, uint8_t *buffer, int len) __attribute__((weak));
/* CRC */
uint8_t sensirion_crc8_calculate(const uint8_t *data, uint16_t count) __attribute__((weak));
/* Interrupts */
int8_t scd4x_disable_interrupts(void) __attribute__((weak));
int8_t scd4x_enable_interrupts(void) __attribute__((weak));
/* delay function */
void delay_ms(int delay_ms) __attribute__((weak));

/*
 * Public functions
 */

int8_t scd4x_send_cmd(scd4x_cmd_t cmd)
{
	uint8_t buffer[32];
	int result;

	// start measurement
	buffer[0] = cmd >> 8;
	buffer[1] = cmd & 0x00ff;
	scd4x_disable_interrupts();
	result = scd4x_i2c_transmit(SCD4X_I2C_ADDRESS<<1, buffer, 2);
	scd4x_enable_interrupts();
	if (result != 0) {
		return SCD4X_ERROR;
	}

	/* Sensirion sensors return NACK after last byte (so NACK at the end is ok) */
	return SCD4X_OK;
}

int8_t scd4x_get_serial(uint8_t serial[6])
{
	uint8_t buffer[16];
	int result;

	scd4x_send_cmd(SCD4X_GET_SERIAL_NUMBER);
	scd4x_disable_interrupts();
	result = scd4x_i2c_receive(SCD4X_I2C_ADDRESS << 1, buffer, 9);
	scd4x_enable_interrupts();
	if (result != 0) {
		return SCD4X_ERROR;
	}
	return SCD4X_OK;
}

int8_t scd4x_read_data(uint8_t *buffer, int len)
{
	return SCD4X_OK;
}

int8_t scd4x_start_periodic_measurement( void )
{
	return scd4x_send_cmd(SCD4X_START_PERIODIC_MEASUREMENT);
}

int8_t scd4x_stop_periodic_measurement( void )
{
	return scd4x_send_cmd(SCD4X_STOP_PERIODIC_MEASUREMENT);
}

int8_t scd4x_perform_factory_reset( void )
{
	return scd4x_send_cmd(SCD4X_PERFORM_FACTORY_RESET);
}

int8_t scd4x_read_measurement(uint16_t *co2, int16_t *temperature, uint16_t *relative_humidity)
{
	uint8_t buffer[32];
	int result;

	/* start measurement */
	buffer[0] = SCD4X_READ_MEASUREMENT >> 8;
	buffer[1] = SCD4X_READ_MEASUREMENT & 0x00ff;
	/* disable interrupts to prevent MODBUS/I2C conflict */
	scd4x_disable_interrupts();
	result = scd4x_i2c_transmit(SCD4X_I2C_ADDRESS<<1, buffer, 2);
	scd4x_enable_interrupts();
	if (result != 0) {
		return SCD4X_ERROR;
	}
	delay_ms(1);
	/* read out */
	scd4x_disable_interrupts();
	result = scd4x_i2c_receive(SCD4X_I2C_ADDRESS<<1, buffer, 9);
	scd4x_enable_interrupts();
	if (result != 0)
	{
		return SCD4X_ERROR;
	}
	/* Convert to T and RH; taken directly from pseudocode in SHT4x datasheet, page 3 */
	uint32_t co2_ticks = (buffer[0] << 8) + buffer[1];
	uint8_t co2_crc = buffer[2];
	uint32_t t_ticks = (buffer[3] << 8) + buffer[4];
	uint8_t t_crc = buffer[5];
	uint32_t rh_ticks = (buffer[6] << 8) + buffer[7];
	uint8_t rh_crc = buffer[8];
	/* check CRC-8 checksum */
	uint8_t crc_correct = sensirion_crc8_calculate(buffer, 2) == co2_crc;
	crc_correct &= sensirion_crc8_calculate(buffer + 3, 2) == t_crc;
	crc_correct &= sensirion_crc8_calculate(buffer + 6, 2) == rh_crc;
	if (!crc_correct) {
		return SCD4X_CRC8_ERROR;
	}
	/* copy to output variables */
	int t_degC = -450 + 10 * 175 * t_ticks / 65535;
	int rh_pRH = 100 * rh_ticks / 65535;
	if (rh_pRH > 100) {
			rh_pRH = 100;
	}
	if (rh_pRH < 0) {
		rh_pRH = 0;
	}
	*co2 = co2_ticks;
	*temperature = t_degC;
	*relative_humidity = rh_pRH;

	return SCD4X_OK;
}