Add skeleton for HTU21DF driver

include/mgos_htu21df.h

@@ -0,0 +1,64 @@
+#pragma once
+
+#include "mgos.h"
+#include "mgos_i2c.h"
+
+#define MGOS_HTU21DF_READ_DELAY (2)
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct mgos_htu21df;
+
+/* 
+ * Initialize a HTU21DF on the I2C bus `i2c` at address specified in `i2caddr`
+ * parameter (default HTU21DF is on address 0x40). The sensor will be polled for
+ * validity, upon success a new `struct mgos_htu21df` is allocated and
+ * returned. If the device could not be found, NULL is returned.
+ */
+struct mgos_htu21df *mgos_htu21df_create(struct mgos_i2c *i2c, uint8_t i2caddr);
+
+/* 
+ * Destroy the data structure associated with a HTU21DF device. The reference
+ * to the pointer of the `struct mgos_htu21df` has to be provided, and upon
+ * successful destruction, its associated memory will be freed and the pointer
+ * set to NULL.
+ */
+void mgos_htu21df_destroy(struct mgos_htu21df **sensor);
+
+/* 
+ * The sensor will be polled for its temperature and humidity data. If the poll
+ * has occured in the last `MGOS_HTU21DF_READ_DELAY` seconds, the cached data is
+ * used (so as not to repeatedly poll the bus upon subsequent calls).
+ */
+bool mgos_htu21df_read(struct mgos_htu21df *sensor);
+
+/*
+ * The sensor will be polled for its temperature and humidity data. If the poll
+ * has occured in the last `MGOS_HTU21DF_READ_DELAY` seconds, the cached data is
+ * used (so as not to repeatedly poll the bus upon subsequent calls).
+ *
+ * The return value is the temperature of the sensor in Celsius, or NAN if no
+ * data was found.
+ */
+float mgos_htu21df_getTemperature(struct mgos_htu21df *sensor);
+
+/*
+ * The sensor will be polled for its temperature and humidity data. If the poll
+ * has occured in the last `MGOS_HTU21DF_READ_DELAY` seconds, the cached data is
+ * used (so as not to repeatedly poll the bus upon subsequent calls).
+ *
+ * The return value is the humidity of the sensor in percent relative humidity,
+ * or NAN if no data was found.
+ */
+float mgos_htu21df_getHumidity(struct mgos_htu21df *sensor);
+
+/*
+ * Initialization function for MGOS -- currently a noop.
+ */
+bool mgos_htu21df_i2c_init(void);
+
+#ifdef __cplusplus
+}
+#endif