Added sht4.c, sht4x.h

sht4x.c

@@ -0,0 +1,83 @@
+/*
+ * sht4x.c
+ *
+ *  Created on: Jun 8, 2021
+ *      Author: user
+ */
+
+#include "sht4x.h"
+
+/*
+ * To be implemented by user
+ */
+
+
+/* TODO prejmenovat vsechny na sht4x_* */
+/* I2C */
+int8_t i2c_transmit(uint8_t address, uint8_t *buffer, int len) __attribute__((weak));
+int8_t 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 sht4x_disable_interrupts(void) __attribute__((weak));
+int8_t sht4x_enable_interrupts(void) __attribute__((weak));
+/* delay function */
+void sht4x_delay_ms(int delay_ms) __attribute__((weak));
+
+int8_t sht4x_send_cmd(sht4x_cmd_t cmd)
+{
+	return SHT4X_OK;
+}
+
+int8_t sht4x_read_data(uint8_t *buffer, int len)
+{
+	return SHT4X_OK;
+}
+
+int8_t sht4x_measure(int16_t *temperature, uint16_t *relative_humidity)
+{
+	uint8_t buffer[32];
+	int result;
+
+	/* start measurement */
+	buffer[0] = SHT4X_START_MEAS_HIGH_PRECISION;
+	/* disable interrupts to prevent modbus/i2c conflict */
+	sht4x_disable_interrupts();
+	result = i2c_transmit(SHT4X_I2C_ADDRESS<<1, buffer, 1);
+	sht4x_enable_interrupts();
+	if (result != 0) {
+		return SHT4X_ERROR;
+	}
+	sht4x_delay_ms(10); /* 10 ms should be enough */
+	/* read out */
+	sht4x_disable_interrupts();
+	result = i2c_receive(SHT4X_I2C_ADDRESS<<1, buffer, 6);
+	sht4x_enable_interrupts();
+	if (result != 0) {
+		return SHT4X_ERROR;
+	}
+	/* Convert to T and RH; taken directly from pseudocode in SHT4x datasheet, page 3 */
+	uint32_t t_ticks = (buffer[0] << 8) + buffer[1];
+	uint8_t t_crc = buffer[2];
+	uint32_t rh_ticks = (buffer[3] << 8) + buffer[4];
+	uint8_t rh_crc = buffer[5];
+	/* check CRC-8 checksum */
+	uint8_t crc_correct = sensirion_crc8_calculate(buffer, 2) == t_crc;
+	crc_correct &= sensirion_crc8_calculate(buffer + 3, 2) == rh_crc;
+	if (!crc_correct) {
+		return SHT4X_CRC8_ERROR;
+	}
+	/* copy data to output variables */
+	int t_degC = -450 + 10 * 175 * t_ticks / 65535; /* temperature * 10 */
+	int rh_pRH = -6 + 125 * rh_ticks / 65535;
+	if (rh_pRH > 100) {
+			rh_pRH = 100;
+	}
+	if (rh_pRH < 0) {
+		rh_pRH = 0;
+	}
+	*temperature = t_degC;
+	*relative_humidity = rh_pRH;
+
+	return SHT4X_OK;
+}