FreeRTOS

[armadillo_firmware.git] / FreeRTOS / Source / include / task.h

/*
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*/


#ifndef INC_FREERTOS_H
        #error "#include FreeRTOS.h" must appear in source files before "#include task.h"
#endif



#ifndef TASK_H
#define TASK_H

#include "portable.h"
#include "list.h"

#ifdef __cplusplus
extern "C" {
#endif

/*-----------------------------------------------------------
 * MACROS AND DEFINITIONS
 *----------------------------------------------------------*/

#define tskKERNEL_VERSION_NUMBER "V6.0.4"

/**
 * task. h
 *
 * Type by which tasks are referenced.  For example, a call to xTaskCreate
 * returns (via a pointer parameter) an xTaskHandle variable that can then
 * be used as a parameter to vTaskDelete to delete the task.
 *
 * \page xTaskHandle xTaskHandle
 * \ingroup Tasks
 */
typedef void * xTaskHandle;

/*
 * Used internally only.
 */
typedef struct xTIME_OUT
{
        portBASE_TYPE xOverflowCount;
        portTickType  xTimeOnEntering;
} xTimeOutType;

/*
 * Defines the memory ranges allocated to the task when an MPU is used.
 */
typedef struct xMEMORY_REGION
{
        void *pvBaseAddress;
        unsigned long ulLengthInBytes;
        unsigned long ulParameters;
} xMemoryRegion;

/*
 * Parameters required to create an MPU protected task.
 */
typedef struct xTASK_PARAMTERS
{
        pdTASK_CODE pvTaskCode;
        const signed char * const pcName;
        unsigned short usStackDepth;
        void *pvParameters;
        unsigned portBASE_TYPE uxPriority;
        portSTACK_TYPE *puxStackBuffer;
        xMemoryRegion xRegions[ portNUM_CONFIGURABLE_REGIONS ];
} xTaskParameters;

/*
 * Defines the priority used by the idle task.  This must not be modified.
 *
 * \ingroup TaskUtils
 */
#define tskIDLE_PRIORITY                        ( ( unsigned portBASE_TYPE ) 0 )

/**
 * task. h
 *
 * Macro for forcing a context switch.
 *
 * \page taskYIELD taskYIELD
 * \ingroup SchedulerControl
 */
#define taskYIELD()                                     portYIELD()

/**
 * task. h
 *
 * Macro to mark the start of a critical code region.  Preemptive context
 * switches cannot occur when in a critical region.
 *
 * NOTE: This may alter the stack (depending on the portable implementation)
 * so must be used with care!
 *
 * \page taskENTER_CRITICAL taskENTER_CRITICAL
 * \ingroup SchedulerControl
 */
#define taskENTER_CRITICAL()            portENTER_CRITICAL()

/**
 * task. h
 *
 * Macro to mark the end of a critical code region.  Preemptive context
 * switches cannot occur when in a critical region.
 *
 * NOTE: This may alter the stack (depending on the portable implementation)
 * so must be used with care!
 *
 * \page taskEXIT_CRITICAL taskEXIT_CRITICAL
 * \ingroup SchedulerControl
 */
#define taskEXIT_CRITICAL()                     portEXIT_CRITICAL()

/**
 * task. h
 *
 * Macro to disable all maskable interrupts.
 *
 * \page taskDISABLE_INTERRUPTS taskDISABLE_INTERRUPTS
 * \ingroup SchedulerControl
 */
#define taskDISABLE_INTERRUPTS()        portDISABLE_INTERRUPTS()

/**
 * task. h
 *
 * Macro to enable microcontroller interrupts.
 *
 * \page taskENABLE_INTERRUPTS taskENABLE_INTERRUPTS
 * \ingroup SchedulerControl
 */
#define taskENABLE_INTERRUPTS()         portENABLE_INTERRUPTS()

/* Definitions returned by xTaskGetSchedulerState(). */
#define taskSCHEDULER_NOT_STARTED       0
#define taskSCHEDULER_RUNNING           1
#define taskSCHEDULER_SUSPENDED         2

/*-----------------------------------------------------------
 * TASK CREATION API
 *----------------------------------------------------------*/

/**
 * task. h
 *<pre>
 portBASE_TYPE xTaskCreate(
                                                          pdTASK_CODE pvTaskCode,
                                                          const char * const pcName,
                                                          unsigned short usStackDepth,
                                                          void *pvParameters,
                                                          unsigned portBASE_TYPE uxPriority,
                                                          xTaskHandle *pvCreatedTask
                                                  );</pre>
 *
 * Create a new task and add it to the list of tasks that are ready to run.
 * 
 * xTaskCreate() can only be used to create a task that has unrestricted
 * access to the entire microcontroller memory map.  Systems that include MPU
 * support can alternatively create an MPU constrained task using 
 * xTaskCreateRestricted().
 *
 * @param pvTaskCode Pointer to the task entry function.  Tasks
 * must be implemented to never return (i.e. continuous loop).
 *
 * @param pcName A descriptive name for the task.  This is mainly used to
 * facilitate debugging.  Max length defined by tskMAX_TASK_NAME_LEN - default
 * is 16.
 *
 * @param usStackDepth 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 16 bits wide and usStackDepth is defined as 100, 200 bytes
 * will be allocated for stack storage.
 *
 * @param pvParameters Pointer that will be used as the parameter for the task
 * being created.
 *
 * @param uxPriority The priority at which the task should run.  Systems that
 * include MPU support can optionally create tasks in a privileged (system)
 * mode by setting bit portPRIVILEGE_BIT of the priority parameter.  For
 * example, to create a privileged task at priority 2 the uxPriority parameter
 * should be set to ( 2 | portPRIVILEGE_BIT ).
 *
 * @param pvCreatedTask Used to pass back a handle by which the created task
 * can be referenced.
 *
 * @return pdPASS if the task was successfully created and added to a ready
 * list, otherwise an error code defined in the file errors. h
 *
 * Example usage:
   <pre>
 // Task to be created.
 void vTaskCode( void * pvParameters )
 {
         for( ;; )
         {
                 // Task code goes here.
         }
 }

 // Function that creates a task.
 void vOtherFunction( void )
 {
 static unsigned char ucParameterToPass;
 xTaskHandle xHandle;

         // Create the task, storing the handle.  Note that the passed parameter ucParameterToPass
         // must exist for the lifetime of the task, so in this case is declared static.  If it was just an
         // an automatic stack variable it might no longer exist, or at least have been corrupted, by the time
         // the new task attempts to access it.
         xTaskCreate( vTaskCode, "NAME", STACK_SIZE, &ucParameterToPass, tskIDLE_PRIORITY, &xHandle );

         // Use the handle to delete the task.
         vTaskDelete( xHandle );
 }
   </pre>
 * \defgroup xTaskCreate xTaskCreate
 * \ingroup Tasks
 */
#define xTaskCreate( pvTaskCode, pcName, usStackDepth, pvParameters, uxPriority, pxCreatedTask ) xTaskGenericCreate( ( pvTaskCode ), ( pcName ), ( usStackDepth ), ( pvParameters ), ( uxPriority ), ( pxCreatedTask ), ( NULL ), ( NULL ) )

/**
 * task. h
 *<pre>
 portBASE_TYPE xTaskCreateRestricted( xTaskParameters *pxTaskDefinition, xTaskHandle *pxCreatedTask );</pre>
 *
 * xTaskCreateRestricted() should only be used in systems that include an MPU
 * implementation.
 *
 * Create a new task and add it to the list of tasks that are ready to run.
 * The function parameters define the memory regions and associated access
 * permissions allocated to the task.
 *
 * @param pxTaskDefinition Pointer to a structure that contains a member
 * for each of the normal xTaskCreate() parameters (see the xTaskCreate() API
 * documentation) plus an optional stack buffer and the memory region 
 * definitions.
 *
 * @param pxCreatedTask Used to pass back a handle by which the created task
 * can be referenced.
 *
 * @return pdPASS if the task was successfully created and added to a ready
 * list, otherwise an error code defined in the file errors. h
 *
 * Example usage:
   <pre>
// Create an xTaskParameters structure that defines the task to be created.
static const xTaskParameters xCheckTaskParameters =
{
        vATask,         // pvTaskCode - the function that implements the task.
        "ATask",        // pcName - just a text name for the task to assist debugging.
        100,            // usStackDepth - the stack size DEFINED IN WORDS.
        NULL,           // pvParameters - passed into the task function as the function parameters.
        ( 1UL | portPRIVILEGE_BIT ),// uxPriority - task priority, set the portPRIVILEGE_BIT if the task should run in a privileged state.
        cStackBuffer,// puxStackBuffer - the buffer to be used as the task stack.

        // xRegions - Allocate up to three separate memory regions for access by
        // the task, with appropriate access permissions.  Different processors have
        // different memory alignment requirements - refer to the FreeRTOS documentation
        // for full information.
        {                                                                                       
                // Base address                                 Length  Parameters
        { cReadWriteArray,                              32,             portMPU_REGION_READ_WRITE },
        { cReadOnlyArray,                               32,             portMPU_REGION_READ_ONLY },
        { cPrivilegedOnlyAccessArray,   128,    portMPU_REGION_PRIVILEGED_READ_WRITE }
        }
};

int main( void )
{
xTaskHandle xHandle;

        // Create a task from the const structure defined above.  The task handle
        // is requested (the second parameter is not NULL) but in this case just for
        // demonstration purposes as its not actually used.
        xTaskCreateRestricted( &xRegTest1Parameters, &xHandle );

        // Start the scheduler.
        vTaskStartScheduler();

        // Will only get here if there was insufficient memory to create the idle
        // task.
        for( ;; );
}
   </pre>
 * \defgroup xTaskCreateRestricted xTaskCreateRestricted
 * \ingroup Tasks
 */
#define xTaskCreateRestricted( x, pxCreatedTask ) xTaskGenericCreate( ((x)->pvTaskCode), ((x)->pcName), ((x)->usStackDepth), ((x)->pvParameters), ((x)->uxPriority), (pxCreatedTask), ((x)->puxStackBuffer), ((x)->xRegions) )

/**
 * task. h
 *<pre>
 void vTaskAllocateMPURegions( xTaskHandle xTask, const xMemoryRegion * const pxRegions );</pre>
 *
 * Memory regions are assigned to a restricted task when the task is created by
 * a call to xTaskCreateRestricted().  These regions can be redefined using
 * vTaskAllocateMPURegions().
 * 
 * @param xTask The handle of the task being updated.
 *
 * @param xRegions A pointer to an xMemoryRegion structure that contains the
 * new memory region definitions.
 *
 * Example usage:
   <pre>
// Define an array of xMemoryRegion structures that configures an MPU region
// allowing read/write access for 1024 bytes starting at the beginning of the
// ucOneKByte array.  The other two of the maximum 3 definable regions are
// unused so set to zero.
static const xMemoryRegion xAltRegions[ portNUM_CONFIGURABLE_REGIONS ] =
{                                                                                       
        // Base address         Length          Parameters
        { ucOneKByte,           1024,           portMPU_REGION_READ_WRITE },
        { 0,                            0,                      0 },
        { 0,                            0,                      0 }
};

void vATask( void *pvParameters )
{
        // This task was created such that it has access to certain regions of
        // memory as defined by the MPU configuration.  At some point it is 
        // desired that these MPU regions are replaced with that defined in the
        // xAltRegions const struct above.  Use a call to vTaskAllocateMPURegions()
        // for this purpose.  NULL is used as the task handle to indicate that this
        // function should modify the MPU regions of the calling task.
        vTaskAllocateMPURegions( NULL, xAltRegions );
        
        // Now the task can continue its function, but from this point on can only
        // access its stack and the ucOneKByte array (unless any other statically
        // defined or shared regions have been declared elsewhere).
}
   </pre>
 * \defgroup xTaskCreateRestricted xTaskCreateRestricted
 * \ingroup Tasks
 */
void vTaskAllocateMPURegions( xTaskHandle xTask, const xMemoryRegion * const pxRegions ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>void vTaskDelete( xTaskHandle pxTask );</pre>
 *
 * INCLUDE_vTaskDelete must be defined as 1 for this function to be available.
 * See the configuration section for more information.
 *
 * Remove a task from the RTOS real time kernels management.  The task being
 * deleted will be removed from all ready, blocked, suspended and event lists.
 *
 * NOTE:  The idle task is responsible for freeing the kernel allocated
 * memory from tasks that have been deleted.  It is therefore important that
 * the idle task is not starved of microcontroller processing time if your
 * application makes any calls to vTaskDelete ().  Memory allocated by the
 * task code is not automatically freed, and should be freed before the task
 * is deleted.
 *
 * See the demo application file death.c for sample code that utilises
 * vTaskDelete ().
 *
 * @param pxTask The handle of the task to be deleted.  Passing NULL will
 * cause the calling task to be deleted.
 *
 * Example usage:
   <pre>
 void vOtherFunction( void )
 {
 xTaskHandle xHandle;

         // Create the task, storing the handle.
         xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );

         // Use the handle to delete the task.
         vTaskDelete( xHandle );
 }
   </pre>
 * \defgroup vTaskDelete vTaskDelete
 * \ingroup Tasks
 */
void vTaskDelete( xTaskHandle pxTask ) PRIVILEGED_FUNCTION;


/*-----------------------------------------------------------
 * TASK CONTROL API
 *----------------------------------------------------------*/

/**
 * task. h
 * <pre>void vTaskDelay( portTickType xTicksToDelay );</pre>
 *
 * Delay a task for a given number of ticks.  The actual time that the
 * task remains blocked depends on the tick rate.  The constant
 * portTICK_RATE_MS can be used to calculate real time from the tick
 * rate - with the resolution of one tick period.
 *
 * INCLUDE_vTaskDelay must be defined as 1 for this function to be available.
 * See the configuration section for more information.
 *
 *
 * vTaskDelay() specifies a time at which the task wishes to unblock relative to
 * the time at which vTaskDelay() is called.  For example, specifying a block
 * period of 100 ticks will cause the task to unblock 100 ticks after
 * vTaskDelay() is called.  vTaskDelay() does not therefore provide a good method
 * of controlling the frequency of a cyclical task as the path taken through the
 * code, as well as other task and interrupt activity, will effect the frequency
 * at which vTaskDelay() gets called and therefore the time at which the task
 * next executes.  See vTaskDelayUntil() for an alternative API function designed
 * to facilitate fixed frequency execution.  It does this by specifying an
 * absolute time (rather than a relative time) at which the calling task should
 * unblock.
 *
 * @param xTicksToDelay The amount of time, in tick periods, that
 * the calling task should block.
 *
 * Example usage:

 void vTaskFunction( void * pvParameters )
 {
 void vTaskFunction( void * pvParameters )
 {
 // Block for 500ms.
 const portTickType xDelay = 500 / portTICK_RATE_MS;

         for( ;; )
         {
                 // Simply toggle the LED every 500ms, blocking between each toggle.
                 vToggleLED();
                 vTaskDelay( xDelay );
         }
 }

 * \defgroup vTaskDelay vTaskDelay
 * \ingroup TaskCtrl
 */
void vTaskDelay( portTickType xTicksToDelay ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>void vTaskDelayUntil( portTickType *pxPreviousWakeTime, portTickType xTimeIncrement );</pre>
 *
 * INCLUDE_vTaskDelayUntil must be defined as 1 for this function to be available.
 * See the configuration section for more information.
 *
 * Delay a task until a specified time.  This function can be used by cyclical
 * tasks to ensure a constant execution frequency.
 *
 * This function differs from vTaskDelay () in one important aspect:  vTaskDelay () will
 * cause a task to block for the specified number of ticks from the time vTaskDelay () is
 * called.  It is therefore difficult to use vTaskDelay () by itself to generate a fixed
 * execution frequency as the time between a task starting to execute and that task
 * calling vTaskDelay () may not be fixed [the task may take a different path though the
 * code between calls, or may get interrupted or preempted a different number of times
 * each time it executes].
 *
 * Whereas vTaskDelay () specifies a wake time relative to the time at which the function
 * is called, vTaskDelayUntil () specifies the absolute (exact) time at which it wishes to
 * unblock.
 *
 * The constant portTICK_RATE_MS can be used to calculate real time from the tick
 * rate - with the resolution of one tick period.
 *
 * @param pxPreviousWakeTime Pointer to a variable that holds the time at which the
 * task was last unblocked.  The variable must be initialised with the current time
 * prior to its first use (see the example below).  Following this the variable is
 * automatically updated within vTaskDelayUntil ().
 *
 * @param xTimeIncrement The cycle time period.  The task will be unblocked at
 * time *pxPreviousWakeTime + xTimeIncrement.  Calling vTaskDelayUntil with the
 * same xTimeIncrement parameter value will cause the task to execute with
 * a fixed interface period.
 *
 * Example usage:
   <pre>
 // Perform an action every 10 ticks.
 void vTaskFunction( void * pvParameters )
 {
 portTickType xLastWakeTime;
 const portTickType xFrequency = 10;

         // Initialise the xLastWakeTime variable with the current time.
         xLastWakeTime = xTaskGetTickCount ();
         for( ;; )
         {
                 // Wait for the next cycle.
                 vTaskDelayUntil( &xLastWakeTime, xFrequency );

                 // Perform action here.
         }
 }
   </pre>
 * \defgroup vTaskDelayUntil vTaskDelayUntil
 * \ingroup TaskCtrl
 */
void vTaskDelayUntil( portTickType * const pxPreviousWakeTime, portTickType xTimeIncrement ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>unsigned portBASE_TYPE uxTaskPriorityGet( xTaskHandle pxTask );</pre>
 *
 * INCLUDE_xTaskPriorityGet must be defined as 1 for this function to be available.
 * See the configuration section for more information.
 *
 * Obtain the priority of any task.
 *
 * @param pxTask Handle of the task to be queried.  Passing a NULL
 * handle results in the priority of the calling task being returned.
 *
 * @return The priority of pxTask.
 *
 * Example usage:
   <pre>
 void vAFunction( void )
 {
 xTaskHandle xHandle;

         // Create a task, storing the handle.
         xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );

         // ...

         // Use the handle to obtain the priority of the created task.
         // It was created with tskIDLE_PRIORITY, but may have changed
         // it itself.
         if( uxTaskPriorityGet( xHandle ) != tskIDLE_PRIORITY )
         {
                 // The task has changed it's priority.
         }

         // ...

         // Is our priority higher than the created task?
         if( uxTaskPriorityGet( xHandle ) < uxTaskPriorityGet( NULL ) )
         {
                 // Our priority (obtained using NULL handle) is higher.
         }
 }
   </pre>
 * \defgroup uxTaskPriorityGet uxTaskPriorityGet
 * \ingroup TaskCtrl
 */
unsigned portBASE_TYPE uxTaskPriorityGet( xTaskHandle pxTask ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>void vTaskPrioritySet( xTaskHandle pxTask, unsigned portBASE_TYPE uxNewPriority );</pre>
 *
 * INCLUDE_vTaskPrioritySet must be defined as 1 for this function to be available.
 * See the configuration section for more information.
 *
 * Set the priority of any task.
 *
 * A context switch will occur before the function returns if the priority
 * being set is higher than the currently executing task.
 *
 * @param pxTask Handle to the task for which the priority is being set.
 * Passing a NULL handle results in the priority of the calling task being set.
 *
 * @param uxNewPriority The priority to which the task will be set.
 *
 * Example usage:
   <pre>
 void vAFunction( void )
 {
 xTaskHandle xHandle;

         // Create a task, storing the handle.
         xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );

         // ...

         // Use the handle to raise the priority of the created task.
         vTaskPrioritySet( xHandle, tskIDLE_PRIORITY + 1 );

         // ...

         // Use a NULL handle to raise our priority to the same value.
         vTaskPrioritySet( NULL, tskIDLE_PRIORITY + 1 );
 }
   </pre>
 * \defgroup vTaskPrioritySet vTaskPrioritySet
 * \ingroup TaskCtrl
 */
void vTaskPrioritySet( xTaskHandle pxTask, unsigned portBASE_TYPE uxNewPriority ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>void vTaskSuspend( xTaskHandle pxTaskToSuspend );</pre>
 *
 * INCLUDE_vTaskSuspend must be defined as 1 for this function to be available.
 * See the configuration section for more information.
 *
 * Suspend any task.  When suspended a task will never get any microcontroller
 * processing time, no matter what its priority.
 *
 * Calls to vTaskSuspend are not accumulative -
 * i.e. calling vTaskSuspend () twice on the same task still only requires one
 * call to vTaskResume () to ready the suspended task.
 *
 * @param pxTaskToSuspend Handle to the task being suspended.  Passing a NULL
 * handle will cause the calling task to be suspended.
 *
 * Example usage:
   <pre>
 void vAFunction( void )
 {
 xTaskHandle xHandle;

         // Create a task, storing the handle.
         xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );

         // ...

         // Use the handle to suspend the created task.
         vTaskSuspend( xHandle );

         // ...

         // The created task will not run during this period, unless
         // another task calls vTaskResume( xHandle ).

         //...


         // Suspend ourselves.
         vTaskSuspend( NULL );

         // We cannot get here unless another task calls vTaskResume
         // with our handle as the parameter.
 }
   </pre>
 * \defgroup vTaskSuspend vTaskSuspend
 * \ingroup TaskCtrl
 */
void vTaskSuspend( xTaskHandle pxTaskToSuspend ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>void vTaskResume( xTaskHandle pxTaskToResume );</pre>
 *
 * INCLUDE_vTaskSuspend must be defined as 1 for this function to be available.
 * See the configuration section for more information.
 *
 * Resumes a suspended task.
 *
 * A task that has been suspended by one of more calls to vTaskSuspend ()
 * will be made available for running again by a single call to
 * vTaskResume ().
 *
 * @param pxTaskToResume Handle to the task being readied.
 *
 * Example usage:
   <pre>
 void vAFunction( void )
 {
 xTaskHandle xHandle;

         // Create a task, storing the handle.
         xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );

         // ...

         // Use the handle to suspend the created task.
         vTaskSuspend( xHandle );

         // ...

         // The created task will not run during this period, unless
         // another task calls vTaskResume( xHandle ).

         //...


         // Resume the suspended task ourselves.
         vTaskResume( xHandle );

         // The created task will once again get microcontroller processing
         // time in accordance with it priority within the system.
 }
   </pre>
 * \defgroup vTaskResume vTaskResume
 * \ingroup TaskCtrl
 */
void vTaskResume( xTaskHandle pxTaskToResume ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>void xTaskResumeFromISR( xTaskHandle pxTaskToResume );</pre>
 *
 * INCLUDE_xTaskResumeFromISR must be defined as 1 for this function to be
 * available.  See the configuration section for more information.
 *
 * An implementation of vTaskResume() that can be called from within an ISR.
 *
 * A task that has been suspended by one of more calls to vTaskSuspend ()
 * will be made available for running again by a single call to
 * xTaskResumeFromISR ().
 *
 * @param pxTaskToResume Handle to the task being readied.
 *
 * \defgroup vTaskResumeFromISR vTaskResumeFromISR
 * \ingroup TaskCtrl
 */
portBASE_TYPE xTaskResumeFromISR( xTaskHandle pxTaskToResume ) PRIVILEGED_FUNCTION;

/*-----------------------------------------------------------
 * SCHEDULER CONTROL
 *----------------------------------------------------------*/

/**
 * task. h
 * <pre>void vTaskStartScheduler( void );</pre>
 *
 * Starts the real time kernel tick processing.  After calling the kernel
 * has control over which tasks are executed and when.  This function
 * does not return until an executing task calls vTaskEndScheduler ().
 *
 * At least one task should be created via a call to xTaskCreate ()
 * before calling vTaskStartScheduler ().  The idle task is created
 * automatically when the first application task is created.
 *
 * See the demo application file main.c for an example of creating
 * tasks and starting the kernel.
 *
 * Example usage:
   <pre>
 void vAFunction( void )
 {
         // Create at least one task before starting the kernel.
         xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL );

         // Start the real time kernel with preemption.
         vTaskStartScheduler ();

         // Will not get here unless a task calls vTaskEndScheduler ()
 }
   </pre>
 *
 * \defgroup vTaskStartScheduler vTaskStartScheduler
 * \ingroup SchedulerControl
 */
void vTaskStartScheduler( void ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>void vTaskEndScheduler( void );</pre>
 *
 * Stops the real time kernel tick.  All created tasks will be automatically
 * deleted and multitasking (either preemptive or cooperative) will
 * stop.  Execution then resumes from the point where vTaskStartScheduler ()
 * was called, as if vTaskStartScheduler () had just returned.
 *
 * See the demo application file main. c in the demo/PC directory for an
 * example that uses vTaskEndScheduler ().
 *
 * vTaskEndScheduler () requires an exit function to be defined within the
 * portable layer (see vPortEndScheduler () in port. c for the PC port).  This
 * performs hardware specific operations such as stopping the kernel tick.
 *
 * vTaskEndScheduler () will cause all of the resources allocated by the
 * kernel to be freed - but will not free resources allocated by application
 * tasks.
 *
 * Example usage:
   <pre>
 void vTaskCode( void * pvParameters )
 {
         for( ;; )
         {
                 // Task code goes here.

                 // At some point we want to end the real time kernel processing
                 // so call ...
                 vTaskEndScheduler ();
         }
 }

 void vAFunction( void )
 {
         // Create at least one task before starting the kernel.
         xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, NULL );

         // Start the real time kernel with preemption.
         vTaskStartScheduler ();

         // Will only get here when the vTaskCode () task has called
         // vTaskEndScheduler ().  When we get here we are back to single task
         // execution.
 }
   </pre>
 *
 * \defgroup vTaskEndScheduler vTaskEndScheduler
 * \ingroup SchedulerControl
 */
void vTaskEndScheduler( void ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>void vTaskSuspendAll( void );</pre>
 *
 * Suspends all real time kernel activity while keeping interrupts (including the
 * kernel tick) enabled.
 *
 * After calling vTaskSuspendAll () the calling task will continue to execute
 * without risk of being swapped out until a call to xTaskResumeAll () has been
 * made.
 *
 * API functions that have the potential to cause a context switch (for example,
 * vTaskDelayUntil(), xQueueSend(), etc.) must not be called while the scheduler
 * is suspended.
 *
 * Example usage:
   <pre>
 void vTask1( void * pvParameters )
 {
         for( ;; )
         {
                 // Task code goes here.

                 // ...

                 // At some point the task wants to perform a long operation during
                 // which it does not want to get swapped out.  It cannot use
                 // taskENTER_CRITICAL ()/taskEXIT_CRITICAL () as the length of the
                 // operation may cause interrupts to be missed - including the
                 // ticks.

                 // Prevent the real time kernel swapping out the task.
                 vTaskSuspendAll ();

                 // Perform the operation here.  There is no need to use critical
                 // sections as we have all the microcontroller processing time.
                 // During this time interrupts will still operate and the kernel
                 // tick count will be maintained.

                 // ...

                 // The operation is complete.  Restart the kernel.
                 xTaskResumeAll ();
         }
 }
   </pre>
 * \defgroup vTaskSuspendAll vTaskSuspendAll
 * \ingroup SchedulerControl
 */
void vTaskSuspendAll( void ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>char xTaskResumeAll( void );</pre>
 *
 * Resumes real time kernel activity following a call to vTaskSuspendAll ().
 * After a call to vTaskSuspendAll () the kernel will take control of which
 * task is executing at any time.
 *
 * @return If resuming the scheduler caused a context switch then pdTRUE is
 *                returned, otherwise pdFALSE is returned.
 *
 * Example usage:
   <pre>
 void vTask1( void * pvParameters )
 {
         for( ;; )
         {
                 // Task code goes here.

                 // ...

                 // At some point the task wants to perform a long operation during
                 // which it does not want to get swapped out.  It cannot use
                 // taskENTER_CRITICAL ()/taskEXIT_CRITICAL () as the length of the
                 // operation may cause interrupts to be missed - including the
                 // ticks.

                 // Prevent the real time kernel swapping out the task.
                 vTaskSuspendAll ();

                 // Perform the operation here.  There is no need to use critical
                 // sections as we have all the microcontroller processing time.
                 // During this time interrupts will still operate and the real
                 // time kernel tick count will be maintained.

                 // ...

                 // The operation is complete.  Restart the kernel.  We want to force
                 // a context switch - but there is no point if resuming the scheduler
                 // caused a context switch already.
                 if( !xTaskResumeAll () )
                 {
                          taskYIELD ();
                 }
         }
 }
   </pre>
 * \defgroup xTaskResumeAll xTaskResumeAll
 * \ingroup SchedulerControl
 */
signed portBASE_TYPE xTaskResumeAll( void ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <pre>signed portBASE_TYPE xTaskIsTaskSuspended( xTaskHandle xTask );</pre>
 *
 * Utility task that simply returns pdTRUE if the task referenced by xTask is
 * currently in the Suspended state, or pdFALSE if the task referenced by xTask
 * is in any other state.
 *
 */
signed portBASE_TYPE xTaskIsTaskSuspended( xTaskHandle xTask ) PRIVILEGED_FUNCTION;

/*-----------------------------------------------------------
 * TASK UTILITIES
 *----------------------------------------------------------*/

/**
 * task. h
 * <PRE>volatile portTickType xTaskGetTickCount( void );</PRE>
 *
 * @return The count of ticks since vTaskStartScheduler was called.
 *
 * \page xTaskGetTickCount xTaskGetTickCount
 * \ingroup TaskUtils
 */
portTickType xTaskGetTickCount( void ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <PRE>unsigned short uxTaskGetNumberOfTasks( void );</PRE>
 *
 * @return The number of tasks that the real time kernel is currently managing.
 * This includes all ready, blocked and suspended tasks.  A task that
 * has been deleted but not yet freed by the idle task will also be
 * included in the count.
 *
 * \page uxTaskGetNumberOfTasks uxTaskGetNumberOfTasks
 * \ingroup TaskUtils
 */
unsigned portBASE_TYPE uxTaskGetNumberOfTasks( void ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <PRE>void vTaskList( char *pcWriteBuffer );</PRE>
 *
 * configUSE_TRACE_FACILITY must be defined as 1 for this function to be
 * available.  See the configuration section for more information.
 *
 * NOTE: This function will disable interrupts for its duration.  It is
 * not intended for normal application runtime use but as a debug aid.
 *
 * Lists all the current tasks, along with their current state and stack
 * usage high water mark.
 *
 * Tasks are reported as blocked ('B'), ready ('R'), deleted ('D') or
 * suspended ('S').
 *
 * @param pcWriteBuffer A buffer into which the above mentioned details
 * will be written, in ascii form.  This buffer is assumed to be large
 * enough to contain the generated report.  Approximately 40 bytes per
 * task should be sufficient.
 *
 * \page vTaskList vTaskList
 * \ingroup TaskUtils
 */
void vTaskList( signed char *pcWriteBuffer ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <PRE>void vTaskGetRunTimeStats( char *pcWriteBuffer );</PRE>
 *
 * configGENERATE_RUN_TIME_STATS must be defined as 1 for this function
 * to be available.  The application must also then provide definitions
 * for portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() and
 * portGET_RUN_TIME_COUNTER_VALUE to configure a peripheral timer/counter
 * and return the timers current count value respectively.  The counter
 * should be at least 10 times the frequency of the tick count.
 *
 * NOTE: This function will disable interrupts for its duration.  It is
 * not intended for normal application runtime use but as a debug aid.
 *
 * Setting configGENERATE_RUN_TIME_STATS to 1 will result in a total
 * accumulated execution time being stored for each task.  The resolution
 * of the accumulated time value depends on the frequency of the timer
 * configured by the portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() macro.
 * Calling vTaskGetRunTimeStats() writes the total execution time of each
 * task into a buffer, both as an absolute count value and as a percentage
 * of the total system execution time.
 *
 * @param pcWriteBuffer A buffer into which the execution times will be
 * written, in ascii form.  This buffer is assumed to be large enough to
 * contain the generated report.  Approximately 40 bytes per task should
 * be sufficient.
 *
 * \page vTaskGetRunTimeStats vTaskGetRunTimeStats
 * \ingroup TaskUtils
 */
void vTaskGetRunTimeStats( signed char *pcWriteBuffer ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <PRE>void vTaskStartTrace( char * pcBuffer, unsigned portBASE_TYPE uxBufferSize );</PRE>
 *
 * Starts a real time kernel activity trace.  The trace logs the identity of
 * which task is running when.
 *
 * The trace file is stored in binary format.  A separate DOS utility called
 * convtrce.exe is used to convert this into a tab delimited text file which
 * can be viewed and plotted in a spread sheet.
 *
 * @param pcBuffer The buffer into which the trace will be written.
 *
 * @param ulBufferSize The size of pcBuffer in bytes.  The trace will continue
 * until either the buffer in full, or ulTaskEndTrace () is called.
 *
 * \page vTaskStartTrace vTaskStartTrace
 * \ingroup TaskUtils
 */
void vTaskStartTrace( signed char * pcBuffer, unsigned long ulBufferSize ) PRIVILEGED_FUNCTION;

/**
 * task. h
 * <PRE>unsigned long ulTaskEndTrace( void );</PRE>
 *
 * Stops a kernel activity trace.  See vTaskStartTrace ().
 *
 * @return The number of bytes that have been written into the trace buffer.
 *
 * \page usTaskEndTrace usTaskEndTrace
 * \ingroup TaskUtils
 */
unsigned long ulTaskEndTrace( void ) PRIVILEGED_FUNCTION;

/**
 * task.h
 * <PRE>unsigned portBASE_TYPE uxTaskGetStackHighWaterMark( xTaskHandle xTask );</PRE>
 *
 * INCLUDE_uxTaskGetStackHighWaterMark must be set to 1 in FreeRTOSConfig.h for
 * this function to be available.
 *
 * Returns the high water mark of the stack associated with xTask.  That is,
 * the minimum free stack space there has been (in bytes) since the task
 * started.  The smaller the returned number the closer the task has come
 * to overflowing its stack.
 *
 * @param xTask Handle of the task associated with the stack to be checked.
 * Set xTask to NULL to check the stack of the calling task.
 *
 * @return The smallest amount of free stack space there has been (in bytes)
 * since the task referenced by xTask was created.
 */
unsigned portBASE_TYPE uxTaskGetStackHighWaterMark( xTaskHandle xTask ) PRIVILEGED_FUNCTION;

/**
 * task.h
 * <pre>void vTaskSetApplicationTaskTag( xTaskHandle xTask, pdTASK_HOOK_CODE pxHookFunction );</pre>
 *
 * Sets pxHookFunction to be the task hook function used by the task xTask.
 * Passing xTask as NULL has the effect of setting the calling tasks hook
 * function.
 */
void vTaskSetApplicationTaskTag( xTaskHandle xTask, pdTASK_HOOK_CODE pxHookFunction ) PRIVILEGED_FUNCTION;

/**
 * task.h
 * <pre>void xTaskGetApplicationTaskTag( xTaskHandle xTask );</pre>
 *
 * Returns the pxHookFunction value assigned to the task xTask.
 */
pdTASK_HOOK_CODE xTaskGetApplicationTaskTag( xTaskHandle xTask ) PRIVILEGED_FUNCTION;

/**
 * task.h
 * <pre>portBASE_TYPE xTaskCallApplicationTaskHook( xTaskHandle xTask, pdTASK_HOOK_CODE pxHookFunction );</pre>
 *
 * Calls the hook function associated with xTask.  Passing xTask as NULL has
 * the effect of calling the Running tasks (the calling task) hook function.
 *
 * pvParameter is passed to the hook function for the task to interpret as it
 * wants.
 */
portBASE_TYPE xTaskCallApplicationTaskHook( xTaskHandle xTask, void *pvParameter ) PRIVILEGED_FUNCTION;


/*-----------------------------------------------------------
 * SCHEDULER INTERNALS AVAILABLE FOR PORTING PURPOSES
 *----------------------------------------------------------*/

/*
 * THIS FUNCTION MUST NOT BE USED FROM APPLICATION CODE.  IT IS ONLY
 * INTENDED FOR USE WHEN IMPLEMENTING A PORT OF THE SCHEDULER AND IS
 * AN INTERFACE WHICH IS FOR THE EXCLUSIVE USE OF THE SCHEDULER.
 *
 * Called from the real time kernel tick (either preemptive or cooperative),
 * this increments the tick count and checks if any tasks that are blocked
 * for a finite period required removing from a blocked list and placing on
 * a ready list.
 */
void vTaskIncrementTick( void ) PRIVILEGED_FUNCTION;

/*
 * THIS FUNCTION MUST NOT BE USED FROM APPLICATION CODE.  IT IS AN
 * INTERFACE WHICH IS FOR THE EXCLUSIVE USE OF THE SCHEDULER.
 *
 * THIS FUNCTION MUST BE CALLED WITH INTERRUPTS DISABLED.
 *
 * Removes the calling task from the ready list and places it both
 * on the list of tasks waiting for a particular event, and the
 * list of delayed tasks.  The task will be removed from both lists
 * and replaced on the ready list should either the event occur (and
 * there be no higher priority tasks waiting on the same event) or
 * the delay period expires.
 *
 * @param pxEventList The list containing tasks that are blocked waiting
 * for the event to occur.
 *
 * @param xTicksToWait The maximum amount of time that the task should wait
 * for the event to occur.  This is specified in kernel ticks,the constant
 * portTICK_RATE_MS can be used to convert kernel ticks into a real time
 * period.
 */
void vTaskPlaceOnEventList( const xList * const pxEventList, portTickType xTicksToWait ) PRIVILEGED_FUNCTION;

/*
 * THIS FUNCTION MUST NOT BE USED FROM APPLICATION CODE.  IT IS AN
 * INTERFACE WHICH IS FOR THE EXCLUSIVE USE OF THE SCHEDULER.
 *
 * THIS FUNCTION MUST BE CALLED WITH INTERRUPTS DISABLED.
 *
 * Removes a task from both the specified event list and the list of blocked
 * tasks, and places it on a ready queue.
 *
 * xTaskRemoveFromEventList () will be called if either an event occurs to
 * unblock a task, or the block timeout period expires.
 *
 * @return pdTRUE if the task being removed has a higher priority than the task
 * making the call, otherwise pdFALSE.
 */
signed portBASE_TYPE xTaskRemoveFromEventList( const xList * const pxEventList ) PRIVILEGED_FUNCTION;

/*
 * THIS FUNCTION MUST NOT BE USED FROM APPLICATION CODE.  IT IS AN
 * INTERFACE WHICH IS FOR THE EXCLUSIVE USE OF THE SCHEDULER.
 *
 * INCLUDE_vTaskCleanUpResources and INCLUDE_vTaskSuspend must be defined as 1
 * for this function to be available.
 * See the configuration section for more information.
 *
 * Empties the ready and delayed queues of task control blocks, freeing the
 * memory allocated for the task control block and task stacks as it goes.
 */
void vTaskCleanUpResources( void ) PRIVILEGED_FUNCTION;

/*
 * THIS FUNCTION MUST NOT BE USED FROM APPLICATION CODE.  IT IS ONLY
 * INTENDED FOR USE WHEN IMPLEMENTING A PORT OF THE SCHEDULER AND IS
 * AN INTERFACE WHICH IS FOR THE EXCLUSIVE USE OF THE SCHEDULER.
 *
 * Sets the pointer to the current TCB to the TCB of the highest priority task
 * that is ready to run.
 */
void vTaskSwitchContext( void ) PRIVILEGED_FUNCTION;

/*
 * Return the handle of the calling task.
 */
xTaskHandle xTaskGetCurrentTaskHandle( void ) PRIVILEGED_FUNCTION;

/*
 * Capture the current time status for future reference.
 */
void vTaskSetTimeOutState( xTimeOutType * const pxTimeOut ) PRIVILEGED_FUNCTION;

/*
 * Compare the time status now with that previously captured to see if the
 * timeout has expired.
 */
portBASE_TYPE xTaskCheckForTimeOut( xTimeOutType * const pxTimeOut, portTickType * const pxTicksToWait ) PRIVILEGED_FUNCTION;

/*
 * Shortcut used by the queue implementation to prevent unnecessary call to
 * taskYIELD();
 */
void vTaskMissedYield( void ) PRIVILEGED_FUNCTION;

/*
 * Returns the scheduler state as taskSCHEDULER_RUNNING,
 * taskSCHEDULER_NOT_STARTED or taskSCHEDULER_SUSPENDED.
 */
portBASE_TYPE xTaskGetSchedulerState( void ) PRIVILEGED_FUNCTION;

/*
 * Raises the priority of the mutex holder to that of the calling task should
 * the mutex holder have a priority less than the calling task.
 */
void vTaskPriorityInherit( xTaskHandle * const pxMutexHolder ) PRIVILEGED_FUNCTION;

/*
 * Set the priority of a task back to its proper priority in the case that it
 * inherited a higher priority while it was holding a semaphore.
 */
void vTaskPriorityDisinherit( xTaskHandle * const pxMutexHolder ) PRIVILEGED_FUNCTION;

/*
 * Generic version of the task creation function which is in turn called by the
 * xTaskCreate() and xTaskCreateRestricted() macros.
 */
signed portBASE_TYPE xTaskGenericCreate( pdTASK_CODE pvTaskCode, const signed char * const pcName, unsigned short usStackDepth, void *pvParameters, unsigned portBASE_TYPE uxPriority, xTaskHandle *pxCreatedTask, portSTACK_TYPE *puxStackBuffer, const xMemoryRegion * const xRegions ) PRIVILEGED_FUNCTION;

#ifdef __cplusplus
}
#endif
#endif /* TASK_H */