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

src/mgos_htu21df.c

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "mgos.h"
+#include "mgos_htu21df_internal.h"
+#include "mgos_i2c.h"
+
+// Datasheet:
+// https://cdn-shop.adafruit.com/datasheets/1899_HTU21D.pdf
+
+// Private functions follow
+// Private functions end
+
+// Public functions follow
+struct mgos_htu21df *mgos_htu21df_create(struct mgos_i2c *i2c, uint8_t i2caddr) {
+  struct mgos_htu21df *sensor;
+
+  if (!i2c) return NULL;
+
+  sensor=calloc(1, sizeof(struct mgos_htu21df));
+  if (!sensor) return NULL;
+  sensor->i2caddr=i2caddr;
+  sensor->i2c=i2c;
+  sensor->last_read_time=0;
+
+  LOG(LL_INFO, ("HTU21DF created at I2C 0x%02x", i2caddr));
+  return sensor;
+}
+
+void mgos_htu21df_destroy(struct mgos_htu21df **sensor) {
+  if (!*sensor) return;
+  free (*sensor);
+  *sensor=NULL;
+  return;
+}
+
+bool mgos_htu21df_read(struct mgos_htu21df *sensor) {
+  double now = mg_time();
+
+  if (!sensor || !sensor->i2c)
+    return false;
+
+  if (now - sensor->last_read_time < MGOS_HTU21DF_READ_DELAY) {
+    return true;
+  }
+  // Read out sensor data here 
+  //
+ 
+  LOG(LL_DEBUG, ("temperature=%.2fC humidity=%.1f%%", sensor->temperature, sensor->humidity));
+  sensor->last_read_time=now;
+  return true;
+}
+
+float mgos_htu21df_getTemperature(struct mgos_htu21df *sensor) {
+  if (!mgos_htu21df_read(sensor)) return NAN;
+
+  return sensor->temperature;
+}
+
+float mgos_htu21df_getHumidity(struct mgos_htu21df *sensor) {
+  if (!mgos_htu21df_read(sensor)) return NAN;
+
+  return sensor->humidity;
+}
+
+bool mgos_htu21df_i2c_init(void) {
+  return true;
+}
+// Public functions end

src/mgos_htu21df_internal.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include "mgos.h"
+#include "mgos_i2c.h"
+#include "mgos_htu21df.h"
+#include <math.h>
+
+#define MGOS_HTU21DF_DEFAULT_I2CADDR       (0x40)
+
+#define MGOS_HTU21DF_READTEMP              (0xE3)
+#define MGOS_HTU21DF_READHUM               (0xE5)
+#define MGOS_HTU21DF_WRITEREG              (0xE6)
+#define MGOS_HTU21DF_READREG               (0xE7)
+#define MGOS_HTU21DF_RESET                 (0xFE)
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct mgos_htu21df {
+  struct mgos_i2c *i2c;
+  uint8_t i2caddr;
+  double last_read_time;
+
+  float humidity, temperature;
+};
+
+#ifdef __cplusplus
+}
+#endif