Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem TCP & FAT Training




RTOS Context Switch - Step 3
[Detailed Example]

The RTOS tick interrupt executes

The ISR source code is given below. The comments have been removed to ease reading, but can be viewed on a previous page.

/* Interrupt service routine for the RTOS tick. */ void SIG_OUTPUT_COMPARE1A( void ) { vPortYieldFromTick(); asm volatile ( "reti" ); } /*--------------------------------------------------*/

void vPortYieldFromTick( void ) { portSAVE_CONTEXT();

vTaskIncrementTick(); vTaskSwitchContext(); portRESTORE_CONTEXT();

asm volatile ( "ret" ); } /*--------------------------------------------------*/
SIG_OUTPUT_COMPARE1A() is a naked function, so the first instruction is a call to vPortYieldFromTick(). vPortYieldFromTick() is also a naked function so the AVR execution context is saved explicitly by a call to portSAVE_CONTEXT().

portSAVE_CONTEXT() pushes the entire AVR execution context onto the stack of TaskA, resulting in the stack illustrated below. The stack pointer for TaskA now points to the top of its own context. portSAVE_CONTEXT() completes by storing a copy of the stack pointer. The real time kernel already has copy of the TaskB stack pointer - taken the last time TaskB was suspended.

AtoB3.gif


Next: RTOS Implementation - Detailed Example Step 4



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




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

Latest News

FreeRTOS kernel V10 is available for immediate download. Now MIT licensed.


FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

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