Using FreeRTOS Semaphores in Arduino IDE

#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
  }
}