HCSR04: Modifying implementation and adding examples

Signed-off-by: Abhishek Malik <abhishek.malik@intel.com>

src/hcsr04/hcsr04.c

@@ -0,0 +1,121 @@
+/*
+ * Author: Yevgeniy Kiveisha <yevgeniy.kiveisha@intel.com>
+ * Author: Rafael Neri <rafael.neri@gmail.com>
+ * Author: Jun Kato <i@junkato.jp>
+ * Contributions by: Abhishek Malik <abhishek.malik@intel.com>
+ * Copyright (c) 2014-2015 Intel Corporation.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#include "upm_utilities.h"
+#include "hcsr04.h"
+
+hcsr04_context hcsr04_init(int triggerPin, int echoPin) {
+    // make sure MRAA is initialized
+    int mraa_rv;
+    if ((mraa_rv = mraa_init()) != MRAA_SUCCESS)
+    {
+        printf("%s: mraa_init() failed (%d).\n", __FUNCTION__, mraa_rv);
+        return NULL;
+    }
+
+    hcsr04_context dev = (hcsr04_context) malloc(sizeof(struct _hcsr04_context));
+
+    if(!dev) {
+        return NULL;
+    }
+
+    // initialize the GPIO pins
+    dev->trigPin = mraa_gpio_init(triggerPin);
+    if(!dev->trigPin) {
+        printf("Unable to initialize the trigger pin\n");
+        return NULL;
+    }
+
+    dev->echoPin = mraa_gpio_init(echoPin);
+    if(!dev->echoPin) {
+        printf("Unable to initialize the echo pin\n");
+        return NULL;
+    }
+
+    // Setting direction for the GPIO pins
+    if(mraa_gpio_dir(dev->trigPin, MRAA_GPIO_OUT) != MRAA_SUCCESS) {
+        printf("Unable to set the direction of the trigger Pin\n");
+        return NULL;
+    }
+
+    if(mraa_gpio_dir(dev->echoPin, MRAA_GPIO_IN) != MRAA_SUCCESS) {
+        printf("Unable to set the direction of the echo Pin\n");
+        return NULL;
+    }
+
+    // Setting the trigger pin to logic level 0
+    if(mraa_gpio_write(dev->trigPin, 0) != MRAA_SUCCESS)
+        return NULL;
+
+    // initialize the interrupt counter
+    dev->interruptCounter = 0;
+
+    return dev;
+}
+
+void hcsr04_close(hcsr04_context dev) {
+    mraa_gpio_close(dev->trigPin);
+    mraa_gpio_close(dev->echoPin);
+    free(dev);
+}
+
+double hcsr04_get_distance(hcsr04_context dev, HCSR04_U unit) {
+    // set value to start cycle right after trigger
+    long cycleLength = 0, sampleTime = 0;
+    struct timeval tv;
+    int reading = 0;
+
+    dev->interruptCounter = 0;
+    gettimeofday(&tv, NULL);
+
+    // The datasheet suggests using cycles of upto 60 ms
+    // being a little libteral and using 70 ms, though a limit
+    // should not be necessary at all
+    cycleLength = (1000000 * tv.tv_sec) + tv.tv_usec + 70000;
+    mraa_gpio_write(dev->trigPin, 1);
+    upm_delay_us(10);
+    mraa_gpio_write(dev->trigPin, 0);
+
+    while(sampleTime < cycleLength) {
+        reading = mraa_gpio_read(dev->echoPin);
+        if(reading == 1 && dev->interruptCounter == 0) {
+            gettimeofday(&tv, NULL);
+            dev->startTime = (1000000 * tv.tv_sec) + tv.tv_usec;
+            dev->interruptCounter++;
+        } else if(reading == 0 && dev->interruptCounter == 1) {
+            gettimeofday(&tv, NULL);
+            dev->endTime = (1000000 * tv.tv_sec) + tv.tv_usec;
+            break;
+        } else {
+            sampleTime = (1000000 * tv.tv_sec) + tv.tv_usec;
+        }
+    }
+
+    if(unit == HCSR04_CM)
+        return ((dev->endTime - dev->startTime)/2)/29.1;
+    else
+        return ((dev->endTime - dev->startTime)/2)/74.1;
+}