Function Deference

Group that contains function that allow the user to defer functions to the FreeRTOS daemon task. More...

Collaboration diagram for Function Deference:

Functions
BaseType_t	xTimerPendFunctionCallFromISR (PendedFunction_t xFunctionToPend, void *pvParameter1, uint32_t ulParameter2, BaseType_t *pxHigherPriorityTaskWoken) PRIVILEGED_FUNCTION
	Used from application interrupt service routines to defer the execution of a function to the RTOS daemon task (the timer service task, hence this function is implemented in timers.c and is prefixed with 'Timer'). More...
BaseType_t	xTimerPendFunctionCall (PendedFunction_t xFunctionToPend, void *pvParameter1, uint32_t ulParameter2, TickType_t xTicksToWait) PRIVILEGED_FUNCTION
	Used to defer the execution of a function to the RTOS daemon task (the timer service task, hence this function is implemented in timers.c and is prefixed with 'Timer'). More...

Detailed Description

Group that contains function that allow the user to defer functions to the FreeRTOS daemon task.

Function Documentation

xTimerPendFunctionCall()

BaseType_t xTimerPendFunctionCall	(	PendedFunction_t	xFunctionToPend,
		void *	pvParameter1,
		uint32_t	ulParameter2,
		TickType_t	xTicksToWait
	)

#include <timers.h>

Used to defer the execution of a function to the RTOS daemon task (the timer service task, hence this function is implemented in timers.c and is prefixed with 'Timer').

Parameters

xFunctionToPend	The function to execute from the timer service/ daemon task. The function must conform to the PendedFunction_t prototype.
pvParameter1	The value of the callback function's first parameter. The parameter has a void * type to allow it to be used to pass any type. For example, unsigned longs can be cast to a void *, or the void * can be used to point to a structure.
ulParameter2	The value of the callback function's second parameter.
xTicksToWait	Calling this function will result in a message being sent to the timer daemon task on a queue. xTicksToWait is the amount of time the calling task should remain in the Blocked state (so not using any processing time) for space to become available on the timer queue if the queue is found to be full.

Returns

pdPASS is returned if the message was successfully sent to the timer daemon task, otherwise pdFALSE is returned.

xTimerPendFunctionCallFromISR()

BaseType_t xTimerPendFunctionCallFromISR	(	PendedFunction_t	xFunctionToPend,
		void *	pvParameter1,
		uint32_t	ulParameter2,
		BaseType_t *	pxHigherPriorityTaskWoken
	)

#include <timers.h>

Used from application interrupt service routines to defer the execution of a function to the RTOS daemon task (the timer service task, hence this function is implemented in timers.c and is prefixed with 'Timer').

Ideally an interrupt service routine (ISR) is kept as short as possible, but sometimes an ISR either has a lot of processing to do, or needs to perform processing that is not deterministic. In these cases xTimerPendFunctionCallFromISR() can be used to defer processing of a function to the RTOS daemon task.

A mechanism is provided that allows the interrupt to return directly to the task that will subsequently execute the pended callback function. This allows the callback function to execute contiguously in time with the interrupt - just as if the callback had executed in the interrupt itself.

Parameters

xFunctionToPend	The function to execute from the timer service/ daemon task. The function must conform to the PendedFunction_t prototype.
pvParameter1	The value of the callback function's first parameter. The parameter has a void * type to allow it to be used to pass any type. For example, unsigned longs can be cast to a void *, or the void * can be used to point to a structure.
ulParameter2	The value of the callback function's second parameter.
pxHigherPriorityTaskWoken	As mentioned above, calling this function will result in a message being sent to the timer daemon task. If the priority of the timer daemon task (which is set using configTIMER_TASK_PRIORITY in FreeRTOSConfig.h) is higher than the priority of the currently running task (the task the interrupt interrupted) then *pxHigherPriorityTaskWoken will be set to pdTRUE within xTimerPendFunctionCallFromISR(), indicating that a context switch should be requested before the interrupt exits. For that reason *pxHigherPriorityTaskWoken must be initialised to pdFALSE. See the example code below.

Returns

pdPASS is returned if the message was successfully sent to the timer daemon task, otherwise pdFALSE is returned.

Example usage:

// The callback function that will execute in the context of the daemon task.
// Note callback functions must all use this same prototype.
void vProcessInterface( void *pvParameter1, uint32_t ulParameter2 )
{
    BaseType_t xInterfaceToService;
 
    // The interface that requires servicing is passed in the second
    // parameter.  The first parameter is not used in this case.
    xInterfaceToService = ( BaseType_t ) ulParameter2;
 
    // ...Perform the processing here...
}
 
// An ISR that receives data packets from multiple interfaces
void vAnISR( void )
{
    BaseType_t xInterfaceToService, xHigherPriorityTaskWoken;
 
    // Query the hardware to determine which interface needs processing.
    xInterfaceToService = prvCheckInterfaces();
 
    // The actual processing is to be deferred to a task.  Request the
    // vProcessInterface() callback function is executed, passing in the
    // number of the interface that needs processing.  The interface to
    // service is passed in the second parameter.  The first parameter is
    // not used in this case.
    xHigherPriorityTaskWoken = pdFALSE;
    xTimerPendFunctionCallFromISR( vProcessInterface, NULL, ( uint32_t ) xInterfaceToService, &xHigherPriorityTaskWoken );
 
    // If xHigherPriorityTaskWoken is now set to pdTRUE then a context
    // switch should be requested.  The macro used is port specific and will
    // be either portYIELD_FROM_ISR() or portEND_SWITCHING_ISR() - refer to
    // the documentation page for the port being used.
    portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
 
}