The FreeRTOS kernel is now an MIT licensed AWS open source project, and these pages are being updated accordingly.

Quality RTOS & Embedded Software

About Contact Support FAQ Download

Menu

Quick Start

Supported MCUs

PDF Books

Trace Tools

Ecosystem

Quick Start Guide

Support Forum

⇓ Download Source ⇓

FreeRTOS+ Ecosystem

FreeRTOS+TCP:
Thread safe TCP/IP stack

SafeRTOS:
TUV certified RTOS

OpenRTOS:
Commercial Licensed RTOS

Fail Safe File System:
Ensures data integrity

FreeRTOS BSPs:
3rd party driver packages

Trace & Visualisation:
Tracealyzer for FreeRTOS

CLI:
Command line interface

WolfSSL SSL / TLS:
Networking security protocols

RTOS Training:
Delivered online or on-site

IO:
read(), write(), ioctl() interface

FreeRTOS+ Lab Projects

FreeRTOS+POSIX:
POSIX threading API

FreeRTOS+FAT:
Thread aware file system

xTimerChangePeriodFromISR
[Timer API]

timers.h

 BaseType_t xTimerChangePeriodFromISR
           (
              TimerHandle_t xTimer,
              TickType_t xNewPeriod,
              BaseType_t *pxHigherPriorityTaskWoken
           );

A version of xTimerChangePeriod() that can be called from an interrupt service routine.

Parameters:

xTimer	The handle of the software timer that is having its period changed.
xNewPeriod	The new period for xTimer. Timer periods are specified in tick periods, so the constant portTICK_PERIOD_MS can be used to convert a time that has been specified in milliseconds. For example, if the timer must expire after 100 ticks, then xNewPeriod should be set to 100. Alternatively, if the timer must expire after 500ms, then xNewPeriod can be set to ( 500 / portTICK_PERIOD_MS ) provided configTICK_RATE_HZ is less than or equal to 1000.
pxHigherPriorityTaskWoken	The timer service/daemon task spends most of its time in the Blocked state, waiting for messages to arrive on the timer command queue. Calling xTimerChangePeriodFromISR() writes a message to the timer command queue, so has the potential to transition the timer service/ daemon task out of the Blocked state. If calling xTimerChangePeriodFromISR() causes the timer service/daemon task to leave the Blocked state, and the timer service/daemon task has a priority equal to or greater than the currently executing task (the task that was interrupted), then *pxHigherPriorityTaskWoken will get set to pdTRUE internally within the xTimerChangePeriodFromISR() function. If xTimerChangePeriodFromISR() sets this value to pdTRUE, then a context switch should be performed before the interrupt exits.

Returns:: pdFAIL will be returned if the command to change the timers period could not be sent to the timer command queue. pdPASS will be returned if the command was successfully sent to the timer command queue. When the command is actually processed will depend on the priority of the timer service/daemon task relative to other tasks in the system. The timer service/daemon task priority is set by the configTIMER_TASK_PRIORITY configuration constant.

Example usage:

/* This scenario assumes xTimer has already been created and started.  When
an interrupt occurs, the period of xTimer should be changed to 500ms. */

/* The interrupt service routine that changes the period of xTimer. */
void vAnExampleInterruptServiceRoutine( void )
{
BaseType_t xHigherPriorityTaskWoken = pdFALSE;

    /* The interrupt has occurred - change the period of xTimer to 500ms.
    xHigherPriorityTaskWoken was set to pdFALSE where it was defined
    (within this function).  As this is an interrupt service routine, only
    FreeRTOS API functions that end in "FromISR" can be used. */
    if( xTimerChangePeriodFromISR( xTimer,
                                   &xHigherPriorityTaskWoken ) != pdPASS )
    {
        /* The command to change the timers period was not executed
        successfully.  Take appropriate action here. */
    }

    /* If xHigherPriorityTaskWoken equals pdTRUE, then a context switch
    should be performed.  The syntax required to perform a context switch
    from inside an ISR varies from port to port, and from compiler to
    compiler.  Inspect the demos for the port you are using to find the
    actual syntax required. */
    if( xHigherPriorityTaskWoken != pdFALSE )
    {
        /* Call the interrupt safe yield function here (actual function
        depends on the FreeRTOS port being used). */
    }
}