Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem

[Timer API]


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

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 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.

Functions that can be deferred to the RTOS daemon task must have the following prototype:

void vPendableFunction( void * pvParameter1, uint32_t ulParameter2 );

The pvParameter1 and ulParameter2 are provided for use by the application code.

INCLUDE_xTimerPendFunctionCall() and configUSE_TIMERS must both be set to 1 for xTimerPendFunctionCallFromISR() to be available.

xFunctionToPend   The function to execute from the timer service/ daemon task. The function must conform to the PendedFunction_t prototype as shown above.
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, integer types 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 xTimerPendFunctionCallFromISR() will result in a message being sent to the RTOS timer daemon task. If the priority of the 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.
pdPASS is returned if the message was successfully sent to the RTOS 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,
                               ( 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 );

[ Back to the top ]    [ About FreeRTOS ]    [ Privacy ]    [ Sitemap ]    [ ]

Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.

Latest News

NXP tweet showing LPC5500 (ARMv8-M Cortex-M33) running FreeRTOS.

Meet Richard Barry and learn about running FreeRTOS on RISC-V at FOSDEM 2019

Version 10.1.1 of the FreeRTOS kernel is available for immediate download. MIT licensed.

View a recording of the "OTA Update Security and Reliability" webinar, presented by TI and AWS.


FreeRTOS and other embedded software careers at AWS.

FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

Espressif ESP32

IAR Partner

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers


STMicro RTOS partner supporting ARM7, ARM Cortex-M3, ARM Cortex-M4 and ARM Cortex-M0

Texas Instruments MCU Developer Network RTOS partner for ARM and MSP430 microcontrollers

OpenRTOS and SafeRTOS

Xilinx Microblaze and Zynq partner