Quality RTOS & Embedded Software

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


Software Timers

Posted by ignaciovarex on February 11, 2019

Just a general question I need a couple timers for a Modbus Slave RTU application. The Modbus spec states that between Modbus frames there is a minimum time of 3.5 times character length and inter byte timeout of 1.5 times character length. So, at 9600 baud 3.5 times character is about 4ms and inter byte timeout of 1.8 ms. Could I get away with using the FreeRTOS software timers? I am using an ARM-M3 EFM32gg990

Software Timers

Posted by rtel on February 11, 2019

That depends on your tick frequency - if the tick is 1KHz (a frequency often used in demos, but faster than most applications) then you can have a timer period with 1ms resolution. Remember the first ms can be between 0.0001ms and 0.99999ms, if the command is received immediately before a tick interrupt or immediately after, so as you need a minimum of 4ms should should have the timer set to 5ms, likewise as you need the minimum of 1.8ms should should set the timer for 3ms.

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

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

Latest News

FreeRTOS v10.2.0 is available for immediate download. MIT licensed, and including RISC-V and ARMv8-M (Cortex-M33) demos.

NXP tweet showing LPC5500 (ARMv8-M Cortex-M33) running FreeRTOS.

View a recording of the "OTA Update Security and Reliability" webinar, presented by TI and AWS.


FreeRTOS and other embedded software careers at AWS.

FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

Cadence Tensilica Cortes

Espressif ESP32

IAR Partner

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers





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