Added mutex semaphore example.

Author: feilipu

examples/AnalogRead_DigitalRead/AnalogRead_DigitalRead.ino

@@ -0,0 +1,117 @@
+#include <Arduino_FreeRTOS.h>
+#include <semphr.h>  // add the FreeRTOS functions for Semaphores (or Flags).
+
+// Declare a mutex Semaphore Handle which we will use to manage the Serial Port.
+// It will be used to ensure only only one Task is accessing this resource at any time.
+SemaphoreHandle_t xSerialSemaphore;
+
+// define two Tasks for DigitalRead & AnalogRead
+void TaskDigitalRead( void *pvParameters );
+void TaskAnalogRead( void *pvParameters );
+
+// the setup function runs once when you press reset or power the board
+void setup() {
+
+  // initialize serial communication at 9600 bits per second:
+  Serial.begin(9600);
+
+  // Semaphores are useful to stop a Task proceeding, where it should be paused to wait,
+  // because it is sharing a resource, such as the Serial port.
+  // Semaphores should only be used whilst the scheduler is running, but we can set it up here.
+  if ( xSerialSemaphore == NULL )  // Check to confirm that the Serial Semaphore has not already been created.
+  {
+    xSerialSemaphore = xSemaphoreCreateMutex();  // Create a mutex semaphore we will use to manage the Serial Port
+    if ( ( xSerialSemaphore ) != NULL )
+      xSemaphoreGive( ( xSerialSemaphore ) );  // Make the Serial Port available for use, by "Giving" the Semaphore.
+  }
+
+  // Now set up two Tasks to run independently.
+  xTaskCreate(
+    TaskDigitalRead
+    ,  (const portCHAR *)"DigitalRead"  // A name just for humans
+    ,  128  // This stack size can be checked & adjusted by reading the Stack Highwater
+    ,  NULL
+    ,  2  // Priority, with 1 being the highest, and 4 being the lowest.
+    ,  NULL );
+
+  xTaskCreate(
+    TaskAnalogRead
+    ,  (const portCHAR *) "AnalogRead"
+    ,  128  // Stack size
+    ,  NULL
+    ,  1  // Priority
+    ,  NULL );
+
+  // Now the Task scheduler, which takes over control of scheduling individual Tasks, is automatically started.
+}
+
+void loop()
+{
+  // Empty. Things are done in Tasks.
+}
+
+/*--------------------------------------------------*/
+/*---------------------- Tasks ---------------------*/
+/*--------------------------------------------------*/
+
+void TaskDigitalRead( void *pvParameters __attribute__((unused)) )  // This is a Task.
+{
+  /*
+    DigitalReadSerial
+    Reads a digital input on pin 2, prints the result to the serial monitor
+
+    This example code is in the public domain.
+  */
+
+  // digital pin 2 has a pushbutton attached to it. Give it a name:
+  uint8_t pushButton = 2;
+
+  // make the pushbutton's pin an input:
+  pinMode(pushButton, INPUT);
+
+  for (;;) // A Task shall never return or exit.
+  {
+    // read the input pin:
+    int buttonState = digitalRead(pushButton);
+
+    // See if we can obtain or "Take" the Serial Semaphore.
+    // If the semaphore is not available, wait 5 ticks of the Scheduler to see if it becomes free.
+    if ( xSemaphoreTake( xSerialSemaphore, ( TickType_t ) 5 ) == pdTRUE )
+    {
+      // We were able to obtain or "Take" the semaphore and can now access the shared resource.
+      // We want to have the Serial Port for us alone, as it takes some time to print,
+      // so we don't want it getting stolen during the middle of a conversion.
+      // print out the state of the button:
+      Serial.println(buttonState);
+
+      xSemaphoreGive( xSerialSemaphore ); // Now free or "Give" the Serial Port for others.
+    }
+
+    vTaskDelay(1);  // one tick delay (15ms) in between reads for stability
+  }
+}
+
+void TaskAnalogRead( void *pvParameters __attribute__((unused)) )  // This is a Task.
+{
+
+  for (;;)
+  {
+    // read the input on analog pin 0:
+    int sensorValue = analogRead(A0);
+
+    // See if we can obtain or "Take" the Serial Semaphore.
+    // If the semaphore is not available, wait 5 ticks of the Scheduler to see if it becomes free.
+    if ( xSemaphoreTake( xSerialSemaphore, ( TickType_t ) 5 ) == pdTRUE )
+    {
+      // We were able to obtain or "Take" the semaphore and can now access the shared resource.
+      // We want to have the Serial Port for us alone, as it takes some time to print,
+      // so we don't want it getting stolen during the middle of a conversion.
+      // print out the value you read:
+      Serial.println(sensorValue);
+
+      xSemaphoreGive( xSerialSemaphore ); // Now free or "Give" the Serial Port for others.
+    }
+
+    vTaskDelay(1);  // one tick delay (15ms) in between reads for stability
+  }
+}