Quality RTOS & Embedded Software

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


FreeRTOS Tick Code
[RTOS Implementation Building Blocks]

The actual source code used by the FreeRTOS AVR port is slightly different to the examples shown on the previous pages. vPortYieldFromTick() is itself implemented as a 'naked' function, and the context is saved and restored within vPortYieldFromTick(). It is done this way due to the implementation of non-preemptive context switches (where a task blocks itself) - which are not described here.

The FreeRTOS implementation of the RTOS tick is therefore (see the comments in the source code snippets for further details):

void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal, naked ) ); void vPortYieldFromTick( void ) __attribute__ ( ( naked ) );

/*--------------------------------------------------*/

/* Interrupt service routine for the RTOS tick. */ void SIG_OUTPUT_COMPARE1A( void ) { /* Call the tick function. */ vPortYieldFromTick();

/* Return from the interrupt. If a context switch has occurred this will return to a different task. */ asm volatile ( "reti" ); } /*--------------------------------------------------*/

void vPortYieldFromTick( void ) { /* This is a naked function so the context is saved. */ portSAVE_CONTEXT();

/* Increment the tick count and check to see if the new tick value has caused a delay period to expire. This function call can cause a task to become ready to run. */ vTaskIncrementTick();

/* See if a context switch is required. Switch to the context of a task made ready to run by vTaskIncrementTick() if it has a priority higher than the interrupted task. */ vTaskSwitchContext();

/* Restore the context. If a context switch has occurred this will restore the context of the task being resumed. */ portRESTORE_CONTEXT();

/* Return from this naked function. */ asm volatile ( "ret" ); } /*--------------------------------------------------*/



Next: RTOS Implementation - The AVR Context


[ 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.


Careers

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

Renesas

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