Quality RTOS & Embedded Software

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




Loading

vTaskSuspendAll() Critical Section

Posted by Ivan on May 11, 2011
Hi all,

For this function:

void vTaskSuspendAll( void )
{
/* A critical section is not required as the variable is of type
portBASE_TYPE. */
++uxSchedulerSuspended;
}


This is generated as a multi-line assembly code and can be interrupted. I was just wondering, why in this case will we not need a critical section? Just because it is of portBASE_TYPE?

Thanks in advance. Cheers!

RE: vTaskSuspendAll() Critical Section

Posted by Dave on May 12, 2011
That is what is says, in the code that you have posted.

RE: vTaskSuspendAll() Critical Section

Posted by Richard Damon on May 14, 2011
The idea is that FreeRTOS assumes that the actually increment will be atomic.

Even if not, vTaskSuspendAll is only called at task level (it doesn't have FromISR) so no interrupt will affect the variable itself. If the increment is not atomic, then it turns out that it doesn't cause problems in this case. If the interrupt occurs after the write of the new value, it will see the new value, if it occurs before, if the old number wasn't zero, no task switch will occur, and since the interrupt doesn't change the value it will return with out task switching (since the number isn't zero) or changing the value. If the number was zero before, and thus seen as zero by the interrupt, a task switch might occur, but if it dose, the value now in uxSchedulerSuspended when the task gets switched back in is by definition 0, the same as before, so no harm in the non-atomic access interrupt by a task switch.

RE: vTaskSuspendAll() Critical Section

Posted by Ivan on May 19, 2011
Thanks loads for the clear explanation. I came to realization that FreeRTOS had wanted for the compiler to compile into atomic machine code that reads, updates and write at one go. Subsequently, I ran through a couple of test cases like you mentioned and found that they were still safe.

Once again, thank you very much for helping me understand.

Warmest Regards :)


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




Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2016 Real Time Engineers Ltd.
Any and all data, files, source code, html content and documentation included in the FreeRTOSTM distribution or available on this site are the exclusive property of Real Time Engineers Ltd.. See the files license.txt (included in the distribution) and this copyright notice for more information. FreeRTOSTM and FreeRTOS.orgTM are trade marks of Real Time Engineers Ltd.

Latest News:

FreeRTOS V9.0.0 is now available for download.


Free TCP/IP and file system demos for the RTOS


Sponsored Links

⇓ Now With No Code Size Limit! ⇓
⇑ Free Download Without Registering ⇑


FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

Renesas Electronics Gold Alliance RTOS Partner.jpg

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers

Atmel RTOS partner supporting ARM Cortex-M3 and AVR32 microcontrollers

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

Xilinx Microblaze and Zynq partner

Silicon Labs low power RTOS partner

Altera RTOS partner for Nios II and Cortex-A9 SoC

Freescale Alliance RTOS Member supporting ARM and ColdFire microcontrollers

Infineon ARM Cortex-M microcontrollers

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

Cypress RTOS partner supporting ARM Cortex-M3

Fujitsu RTOS partner supporting ARM Cortex-M3 and FM3

Microsemi (previously Actel) RTOS partner supporting ARM Cortex-M3

Atollic Partner

IAR Partner

Keil ARM Partner

Embedded Artists