xTaskCreateStatic

Collaboration diagram for xTaskCreateStatic:

task. h

TaskHandle_t xTaskCreateStatic( TaskFunction_t pxTaskCode,
                              const char * const pcName,
                              const configSTACK_DEPTH_TYPE uxStackDepth,
                              void *pvParameters,
                              UBaseType_t uxPriority,
                              StackType_t *puxStackBuffer,
                              StaticTask_t *pxTaskBuffer );

Create a new task and add it to the list of tasks that are ready to run.

Internally, within the FreeRTOS implementation, tasks use two blocks of memory. The first block is used to hold the task's data structures. The second block is used by the task as its stack. If a task is created using xTaskCreate() then both blocks of memory are automatically dynamically allocated inside the xTaskCreate() function. (see https://www.FreeRTOS.org/a00111.html). If a task is created using xTaskCreateStatic() then the application writer must provide the required memory. xTaskCreateStatic() therefore allows a task to be created without using any dynamic memory allocation.

Parameters

pxTaskCode	Pointer to the task entry function. Tasks must be implemented to never return (i.e. continuous loop).
pcName	A descriptive name for the task. This is mainly used to facilitate debugging. The maximum length of the string is defined by configMAX_TASK_NAME_LEN in FreeRTOSConfig.h.
uxStackDepth	The size of the task stack specified as the number of variables the stack can hold - not the number of bytes. For example, if the stack is 32-bits wide and uxStackDepth is defined as 100 then 400 bytes will be allocated for stack storage.
pvParameters	Pointer that will be used as the parameter for the task being created.
uxPriority	The priority at which the task will run.
puxStackBuffer	Must point to a StackType_t array that has at least uxStackDepth indexes - the array will then be used as the task's stack, removing the need for the stack to be allocated dynamically.
pxTaskBuffer	Must point to a variable of type StaticTask_t, which will then be used to hold the task's data structures, removing the need for the memory to be allocated dynamically.

Returns

If neither puxStackBuffer nor pxTaskBuffer are NULL, then the task will be created and a handle to the created task is returned. If either puxStackBuffer or pxTaskBuffer are NULL then the task will not be created and NULL is returned.

Example usage:

   // Dimensions of the buffer that the task being created will use as its stack.
   // NOTE:  This is the number of words the stack will hold, not the number of
   // bytes.  For example, if each stack item is 32-bits, and this is set to 100,
   // then 400 bytes (100 * 32-bits) will be allocated.
#define STACK_SIZE 200
 
   // Structure that will hold the TCB of the task being created.
   StaticTask_t xTaskBuffer;
 
   // Buffer that the task being created will use as its stack.  Note this is
   // an array of StackType_t variables.  The size of StackType_t is dependent on
   // the RTOS port.
   StackType_t xStack[ STACK_SIZE ];
 
   // Function that implements the task being created.
   void vTaskCode( void * pvParameters )
   {
       // The parameter value is expected to be 1 as 1 is passed in the
       // pvParameters value in the call to xTaskCreateStatic().
       configASSERT( ( uint32_t ) pvParameters == 1U );
 
       for( ;; )
       {
           // Task code goes here.
       }
   }
 
   // Function that creates a task.
   void vOtherFunction( void )
   {
       TaskHandle_t xHandle = NULL;
 
       // Create the task without using any dynamic memory allocation.
       xHandle = xTaskCreateStatic(
                     vTaskCode,       // Function that implements the task.
                     "NAME",          // Text name for the task.
                     STACK_SIZE,      // Stack size in words, not bytes.
                     ( void * ) 1,    // Parameter passed into the task.
                     tskIDLE_PRIORITY,// Priority at which the task is created.
                     xStack,          // Array to use as the task's stack.
                     &xTaskBuffer );  // Variable to hold the task's data structure.
 
       // puxStackBuffer and pxTaskBuffer were not NULL, so the task will have
       // been created, and xHandle will be the task's handle.  Use the handle
       // to suspend the task.
       vTaskSuspend( xHandle );
   }