ACS ACR89U-A1 User Manual download pdf (Page 64)

ACR89U-A1 – Application Programming Interface info@acs.com.hk

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Example:

xSemaphoreHandle xMutex;

void vATask( void * pvParameters )

{

// Semaphore cannot be used before a call to

xSemaphoreCreateMutex().

// This is a macro so pass the variable in directly.

xMutex = xSemaphoreCreateRecursiveMutex();

if( xMutex != NULL )

{

// The mutex type semaphore was created successfully.

// The mutex can now be used.

}

6.6.5. xSemaphoreTake

This is a macro to obtain a semaphore. The semaphore must have previously been created with a call

to vSemaphoreCreateBinary(), xSemaphoreCreateMutex() or xSemaphoreCreateCounting().

[semphr.h]

signed portBASE_TYPE xSemaphoreTake

(

xSemaphoreHandle xSemaphore,

portTickType xBlockTime

);

Parameters:

xSemaphore [in] A handle to the semaphore being taken - obtained when the semaphore was

created.

xBlockTime [in] The time in ticks to wait for the semaphore to become available. The macro

portTICK_RATE_MS can be used to convert this to a real time. A block time of zero

can be used to poll the semaphore. Specifying the block time as portMAX_DELAY

will cause the task to block indefinitely (without a timeout).

Returns:

signed portBASE_TYPE pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime expired

without the semaphore becoming available.

Example:

xSemaphoreHandle xSemaphore = NULL;

// A task that creates a semaphore.

void vATask( void * pvParameters )

{

// Create the semaphore to guard a shared resource. As we are using

// the semaphore for mutual exclusion we create a mutex semaphore

// rather than a binary semaphore.

xSemaphore = xSemaphoreCreateMutex();

}

// A task that uses the semaphore.

void vAnotherTask( void * pvParameters )

{

// ... Do other things.

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ACS ACR89U-A1 User Manual Page 64

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