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[Task Creation]

task. h
 TaskHandle_t xTaskCreateStatic( TaskFunction_t pxTaskCode,
                                 const char * const pcName,
                                 const uint32_t ulStackDepth,
                                 void * const pvParameters,
                                 UBaseType_t uxPriority,
                                 StackType_t * const puxStackBuffer,
                                 StaticTask_t * const pxTaskBuffer );

Create a new task and add it to the list of tasks that are ready to run. configSUPPORT_STATIC_ALLOCATION must be set to 1 in FreeRTOSConfig.h for this RTOS API function to be available.

Each task requires RAM that is used to hold the task state, and used by the task as its stack. If a task is created using xTaskCreate() then the required RAM is automatically allocated from the FreeRTOS heap. If a task is created using xTaskCreateStatic() then the RAM is provided by the application writer, which results in a greater number of parameters, but allows the RAM to be statically allocated at compile time. See the Static Vs Dynamic allocation page for more information.

If you are using FreeRTOS-MPU then we recommend you use xTaskCreateRestricted() instead of xTaskCreateStatic().

pxTaskCode Pointer to the task entry function (just the name of the function that implements the task, see the example below).

Tasks are normally implemented as an infinite loop; the function which implements the task must never attempt to return or exit. Tasks can however delete themselves.

pcName A descriptive name for the task. This is mainly used to facilitate debugging, but can also be used to obtain a task handle.

The maximum length of a task's name is defined by configMAX_TASK_NAME_LEN in FreeRTOSConfig.h.

ulStackDepth The puxStackBuffer parameter is used to pass an array of StackType_t variables into xTaskCreateStatic(). ulStackDepth must be set to the number of indexes in the array.

See the FAQ How big should the stack be?

pvParameters The value that is passed as the parameter to the created task.

If pvParameters is set to the address of a variable then the variable must still exist when the created task executes - so it is not valid to pass the address of a stack variable.

uxPriority The priority at which the created task will execute.

Systems that include MPU support can optionally create a task in a privileged (system) mode by setting the bit portPRIVILEGE_BIT in uxPriority. For example, to create a privileged task at priority 2 set uxPriority to ( 2 | portPRIVILEGE_BIT ).

Priorities are asserted to be less than configMAX_PRIORITIES. If configASSERT is undefined, priorities are silently capped at (configMAX_PRIORITIES - 1).

puxStackBuffer Must point to a StackType_t array that has at least ulStackDepth indexes (see the ulStackDepth parameter above) - the array will be used as the task's stack, so it must be persistent (not declared on the stack of a function).
pxTaskBuffer Must point to a variable of type StaticTask_t. The variable will be used to hold the new task's data structures (TCB), so it must be persistent (not declared on the stack of a function).
If neither puxStackBuffer or pxTaskBuffer are NULL then the task will be created, and the task's handle is returned. If either puxStackBuffer or pxTaskBuffer is NULL then the task will not be created and NULL will be 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 == 1UL );

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, /* Number of indexes in the xStack array. */
( 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 );




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