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

Timing precision using ticks

Posted by Matt on December 11, 2008
I have set up a control task that sets a frequency generator up and delays itself for a set period of time in millisecond ticks. The idea is that when it resumes it turns off the frequency generator and an exact known number of rising edges have occurred.

My question is... Just how accurate is tick timing? Presumably, i could run the frequency generator at 1kHz for 1000 ticks and i'd get exactly 1000 rising edges. What are the odds I'd get 999 or 1001.

Now, pushing the limits, what if i were running at 2, 5, 10kHz, how likely am I to be able to stop the frequency generator at exactly the right number of rising edges?

For the sake of argument, lets say there is only ONE task running.

Thanks for your input,
Matt

RE: Timing precision using ticks

Posted by Richard on December 11, 2008
I don't think it can be guaranteed because of jitter in the tick caused by critical sections.

If the port you are using supports interrupt nesting then you can run an interrupt above the system call interrupt priority to avoid any jitter, then it should work well.

Also check the timer peripheral to see if you can do what you want purely using the peripheral hardware.

Regards.

RE: Timing precision using ticks

Posted by Matt on December 11, 2008
Richard, Thanks for your input.

I'm almost to the point where the OS is just a big waste of code space if I take that function out of a task... all I'll be left with is a com task, that could just as easily be polling from the main loop, and a bunch of interrupts.


[ 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