Added DHT library to extras and sample code to examples

examples/dht_sensor/Makefile

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+PROGRAM=dht_sensor
+EXTRA_COMPONENTS = extras/dht
+include ../../common.mk
+

examples/dht_sensor/dht_sensor.c

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+/* 
+ *
+ * This sample code is in the public domain.
+ */
+#include "espressif/esp_common.h"
+#include "esp/uart.h"
+#include "FreeRTOS.h"
+#include "task.h"
+#include "dht.h"
+#include "esp8266.h"
+
+/* An example using the ubiquitous DHT** humidity sensors
+ * to read and print a new temperature and humidity measurement
+ * from a sensor attached to GPIO pin 4.
+ */
+int const dht_gpio = 4;
+
+void dhtMeasurementTask(void *pvParameters)
+{
+  int8_t temperature = 0;
+  int8_t humidity = 0;
+
+  // DHT sensors that come mounted on a PCB generally have
+  // pull-up resistors on the data pin.  It is recommended
+  // to provide an external pull-up resistor otherwise...
+  gpio_set_pullup(dht_gpio, false, false);
+
+  while(1) {
+
+    if (dht_fetch_data(dht_gpio, &humidity, &temperature)) {
+      printf("Humidity: %i%% Temp: %iC\n", humidity, temperature);
+    } else {
+      printf("Could not read data from sensor...");
+    }
+
+    // Three second delay...
+    vTaskDelay(3000 / portTICK_RATE_MS);
+  }
+}
+
+void user_init(void)
+{
+    uart_set_baud(0, 115200);
+    xTaskCreate(dhtMeasurementTask, (signed char *)"dhtMeasurementTask", 256, NULL, 2, NULL);
+}
+

extras/dht/component.mk

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+# Component makefile for extras/dht
+
+INC_DIRS += $(ROOT)extras/dht
+
+# args for passing into compile rule generation
+extras/dht_INC_DIR =  $(ROOT)extras/dht
+extras/dht_SRC_DIR =  $(ROOT)extras/dht
+
+$(eval $(call component_compile_rules,extras/dht))
+

extras/dht/dht.c

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+/*
+ * Part of esp-open-rtos
+ * Copyright (C) 2016 Jonathan Hartsuiker (https://github.com/jsuiker)
+ * BSD Licensed as described in the file LICENSE
+ *
+ */
+
+#include "dht.h"
+#include "string.h"
+#include "task.h"
+#include "esp/gpio.h"
+
+#include <espressif/esp_misc.h> // sdk_os_delay_us
+
+#ifndef DEBUG_DHT
+#define DEBUG_DHT 0
+#endif
+
+#if DEBUG_DHT
+#define debug(fmt, ...) printf("%s" fmt "\n", "dht: ", ## __VA_ARGS__);
+#else
+#define debug(fmt, ...) /* (do nothing) */
+#endif
+
+/* 
+ *  Note:
+ *  A suitable pull-up resistor should be connected to the selected GPIO line
+ *
+ *  __           ______          _______                              ___________________________
+ *    \    A    /      \   C    /       \   DHT duration_data_low    /                           \
+ *     \_______/   B    \______/    D    \__________________________/   DHT duration_data_high    \__
+ *
+ *
+ *  Initializing communications with the DHT requires four 'phases' as follows:
+ * 
+ *  Phase A - MCU pulls signal low for at least 18000 us
+ *  Phase B - MCU allows signal to float back up and waits 20-40us for DHT to pull it low
+ *  Phase C - DHT pulls signal low for ~80us
+ *  Phase D - DHT lets signal float back up for ~80us
+ *  
+ *  After this, the DHT transmits its first bit by holding the signal low for 50us
+ *  and then letting it float back high for a period of time that depends on the data bit.
+ *  duration_data_high is shorter than 50us for a logic '0' and longer than 50us for logic '1'.
+ *
+ *  There are a total of 40 data bits trasnmitted sequentially. These bits are read into a byte array
+ *  of length 5.  The first and third bytes are humidity (%) and temperature (C), respectively.  Bytes 2 and 4
+ *  are zero-filled and the fifth is a checksum such that:
+ *
+ *  byte_5 == (byte_1 + byte_2 + byte_3 + btye_4) & 0xFF
+ *
+*/
+
+/*  
+ *  @pin                    the selected GPIO pin
+ *  @interval               how frequently the pin state is checked in microseconds
+ *  @timeout                maximum length of time to wait for the expected pin state
+ *  @expected_pin_state     high (true) or low (false) pin state
+ *  @counter                pointer to external uint8_t for tallying the duration waited for the pin state
+*/
+
+bool dht_await_pin_state(uint8_t pin, uint8_t interval, uint8_t timeout, bool expected_pin_state, uint8_t * counter) {
+
+    for (*counter = 0; *counter < timeout; *counter+=interval) {
+        if (gpio_read(pin) == expected_pin_state) return true;
+        sdk_os_delay_us(interval);
+    }
+
+    return false;
+}
+
+/*  
+ *  
+ *  
+ *  @pin                    the selected GPIO pin
+ *  @humidity               pointer to external int8_t to store resulting humidity value
+ *  @temperature            pointer to external int8_t to store resulting temperature value
+*/
+
+bool dht_fetch_data(int8_t pin, int8_t * humidity, int8_t * temperature) {
+    int8_t data[40] = {0};
+    int8_t result[5] = {0};
+    uint8_t i = 0;
+
+    uint8_t init_phase_duration = 0;
+    uint8_t duration_data_low = 0;
+    uint8_t duration_data_high = 0;
+
+    gpio_enable(pin, GPIO_OUT_OPEN_DRAIN);
+
+    taskENTER_CRITICAL();
+
+    // Phase 'A' pulling signal low to initiate read sequence
+    gpio_write(pin, 0);
+    sdk_os_delay_us(20000);
+    gpio_write(pin, 1);
+
+    // Step through Phase 'B' at 2us intervals, 40us max
+    if (dht_await_pin_state(pin, 2, 40, false, &init_phase_duration)) {
+        // Step through Phase 'C ' at 2us intervals, 88us max
+        if (dht_await_pin_state(pin, 2, 88, true, &init_phase_duration)) {
+            // Step through Phase 'D' at 2us intervals, 88us max
+            if (dht_await_pin_state(pin, 2, 88, false, &init_phase_duration)) {
+
+                // Read in each of the 40 bits of data...
+                for (i = 0; i < 40; i++) {
+                    if (dht_await_pin_state(pin, 2, 60, true, &duration_data_low)) {
+                        if (dht_await_pin_state(pin, 2, 75, false, &duration_data_high)) {
+                            data[i] = duration_data_high > duration_data_low;
+                        }
+                    }
+                }
+
+                taskEXIT_CRITICAL();
+
+                for (i = 0; i < 40; i++) {
+                    // Read each bit into 'result' byte array...
+                    result[i/8] <<= 1;
+                    result[i/8] |= data[i];
+                }
+
+                if (result[4] == ((result[0] + result[1] + result[2] + result[3]) & 0xFF)) {
+                    // Data valid, checksum succeeded...
+                    *humidity = result[0];
+                    *temperature = result[2];
+                    debug("Successfully retrieved sensor data...");
+                    return true;
+                } else {
+                    debug("Checksum failed, invalid data received from sensor...");
+                }
+
+            } else {
+                debug("Initialization error, problem in phase 'D'...");
+            }
+        } else {
+            debug("Initialization error, problem in phase 'C'...");
+        }
+    } else {
+        debug("Initialization error, problem in phase 'B'...");
+    }
+    
+    taskEXIT_CRITICAL();
+    return false;
+}
+

extras/dht/dht.h

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+/*
+ * Part of esp-open-rtos
+ * Copyright (C) 2016 Jonathan Hartsuiker (https://github.com/jsuiker)
+ * BSD Licensed as described in the file LICENSE
+ *
+ */
+
+#ifndef __DTH_H__
+#define __DHT_H__
+
+#include "FreeRTOS.h"
+
+bool dht_wait_for_pin_state(uint8_t pin, uint8_t interval, uint8_t timeout, bool expected_pin_sate, uint8_t * counter);
+bool dht_fetch_data(int8_t pin, int8_t * humidity, int8_t * temperature);
+
+#endif
+