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


implementation of "yield from ISR...

Posted by Dave Nadler on August 21, 2012
When an ISR does something which logically unblocks a new task (giving a binary semaphore, putting something in a queue), we want to yield. Dumb question perhaps: why not just simulate a timer interrupt ? This would get back to the scheduler quickly and cleanly after the ISR returns. This would mess up anything using the timer for stable timing without some addition work (accumulate partial timer values in the timer ISR and adjust the tick count accordingly), but that's not hard. Might make things simpler ? Still doesn't allow an ISR to mess with queues while running at a higher priority than FreeRTOS. Thoughts ?

Best Regards, Dave

RE: implementation of "yield from ISR...

Posted by Richard on August 22, 2012
Each port does this in a slightly different way. Faking timer interrupts is not possible on all platforms, and would get complex as you would have to know which was a fake interrupt (so only a context switch was performed) and which was a real interrupt requiring the tick to be incremented and a context switch to be performed - the complexity comes when both things happen simultaneously.


RE: implementation of "yield from ISR...

Posted by Dave Nadler on September 2, 2012
Thanks for the concise explanation. I added a fake interrupt to a distinct (non-timer) ISR at priority 1; high-priority ISR can force reschedule by triggering the fake interrupt. Seems nice and clean, on PIC24F anyway.
Thanks again !
Best Regards, Dave

[ 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