commit 0b57fc0a3cf05c64f2d360cf3c28307029fc6580
Author: Jan Mrna <mj370@protonmail.com>
Date:   Sun Jun 12 22:49:01 2022 +0200

    Added files (not yet modified)

diff --git a/scd4x.c b/scd4x.c
new file mode 100644
index 0000000..330d74d
--- /dev/null
+++ b/scd4x.c
@@ -0,0 +1,129 @@
+/*
+ * sht4x.c
+ *
+ *  Created on: Jun 8, 2021
+ *      Author: user
+ */
+
+#include "scd4x.h"
+#include "main.h" /* for uart_disable_interrupts() */
+
+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;
+	result = i2c_transmit(SCD4X_I2C_ADDRESS<<1, buffer, 2);
+	if (result == I2C_ERROR_TX_INCOMPLETE) {
+		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);
+	result = i2c_receive(SCD4X_I2C_ADDRESS << 1, buffer, 9);
+	if (result != I2C_OK) {
+		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
+	// TODO: Check for data ready
+	/*
+	buffer[0] = GET_DATA_READY_STATUS >> 8;
+	buffer[1] =  GET_DATA_READY_STATUS & 0x00ff;
+	result = i2c_transmit(SCD4X_I2C_ADDRESS<<1, buffer, 2);
+	if (result != I2C_OK) {
+		return SCD4X_ERROR;
+	}
+	LL_mDelay(100); // 10 ms should be enough
+	// read out
+	result = i2c_receive(SCD4X_I2C_ADDRESS<<1, buffer, 6);
+	if (result != I2C_OK) {
+		return SCD4X_ERROR;
+	}*/
+
+	// start measurement
+	buffer[0] = SCD4X_READ_MEASUREMENT >> 8;
+	buffer[1] = SCD4X_READ_MEASUREMENT & 0x00ff;
+	// disable interrupts to prevent MODBUS/I2C conflict
+	uart_disable_interrupts();
+	result = i2c_transmit(SCD4X_I2C_ADDRESS<<1, buffer, 2);
+	uart_enable_interrupts();
+	if (result != I2C_OK) {
+		return SCD4X_ERROR;
+	}
+	LL_mDelay(1); // 10 ms should be enough
+	// read out
+	uart_disable_interrupts();
+	result = i2c_receive(SCD4X_I2C_ADDRESS<<1, buffer, 9);
+	uart_enable_interrupts();
+	if (result != I2C_OK)
+	{
+		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 = crc8_calculate(buffer, 2) == co2_crc;
+	crc_correct &= crc8_calculate(buffer + 3, 2) == t_crc;
+	crc_correct &= 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;
+}
diff --git a/scd4x.h b/scd4x.h
new file mode 100644
index 0000000..426ff74
--- /dev/null
+++ b/scd4x.h
@@ -0,0 +1,58 @@
+/*
+ * sht4x.h
+ *
+ *  Created on: Jun 8, 2021
+ *      Author: user
+ */
+
+#ifndef INC_SCD4X_H_
+#define INC_SCD4X_H_
+
+#include "stdint.h"
+#include "stm32l0xx_ll_i2c.h"
+#include "stm32l0xx_ll_utils.h"
+#include "i2c.h"
+#include "crc8.h"
+
+/*
+ * Defines & macros
+ */
+
+#define SCD4X_I2C_ADDRESS 0x62
+
+/*
+ * Return values
+ */
+
+#define SCD4X_OK 0
+#define SCD4X_ERROR -1 // generic error
+#define SCD4X_CRC8_ERROR -2 // checksum failed
+
+/*
+ * Data types
+ */
+
+typedef enum {
+	SCD4X_START_PERIODIC_MEASUREMENT = 0x21B1,
+	SCD4X_READ_MEASUREMENT = 0xEC05,
+	SCD4X_STOP_PERIODIC_MEASUREMENT = 0x3F86,
+	SCD4X_GET_DATA_READY_STATUS = 0xE4B8,
+	SCD4X_PERFORM_FACTORY_RESET = 0x3632,
+	SCD4X_GET_SERIAL_NUMBER = 0x3682
+} scd4x_cmd_t;
+
+/*
+ * Function prototypes
+ */
+
+int8_t scd4x_send_cmd(scd4x_cmd_t cmd);
+int8_t scd4x_read_data(uint8_t *buffer, int len);
+
+int8_t scd4x_start_periodic_measurement( void );
+int8_t scd4x_stop_periodic_measurement( void );
+
+int8_t scd4x_perform_factory_reset( void );
+
+int8_t scd4x_read_measurement(uint16_t * co2, int16_t *temperature, uint16_t *relative_humidity);
+
+#endif /* INC_SCD4X_H_ */