Quality RTOS & Embedded Software

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


Loading

Question about prvInitialiseNewTask() function

Posted by ctc8631 on May 23, 2017

Hello, I'm new learner for freeRTOS, I was confused about code in prvInitialiseNewTask(), when I call xTaskCreate()

```

if( portSTACK_GROWTH < 0 )

{ pxTopOfStack = pxNewTCB->pxStack + ( ulStackDepth - ( uint32t ) 1 ); pxTopOfStack = ( StackTypet * ) ( ( ( portPOINTERSIZETYPE ) pxTopOfStack ) & ( ~( ( portPOINTERSIZETYPE ) portBYTEALIGNMENTMASK ) ) ); } ```

I'm not sure why calculate pxTopOfStack need to minus 1, I read the later code in pxPortInitialiseStack(), when it need stack space, it will minus first and use the space, So I'm not really understand why need -1 here, then it will do alignment, did it waste space? Why not do alignment without -1?

Thanks


Question about prvInitialiseNewTask() function

Posted by rtel on May 23, 2017

This sets the top of stack to be within the stack space, not off the end of it. pxPortInitialiseStack() is port specific, and not all ports will align the top of the stack, but even the ones that do may find the top of stack to coincidentally already be aligned and therefore not make any adjustment.


Question about prvInitialiseNewTask() function

Posted by ctc8631 on May 23, 2017

Mm, I know a little but still a little confused.

I'm using FreeRTOS on cortex-m4. So, in this platform, I do not actually need to make pxTopOfStack-1, right? Because in one situation, the original pxTopOfStack is aligned to 8, if pxTopOfStack-1 then be aligned, it will waste 8bytes, I thought it's a little pity.


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


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

Latest News

Version 10.1.0 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