Quality RTOS & Embedded Software

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




Loading

Difference between blocked and suspended

Posted by Riccardo Manfrin on May 21, 2013
Hi,
I would like to resume this post

https://sourceforge.net/projects/freertos/forums/forum/382005/topic/1742153

I'm not familiar with Freertos (complete ignorant newbie), but I do not comprehend the need to differentiate between suspended and blocked states for a task.

If the difference is really just about the presence of a timeout for blocked state, then in my mind, I see a timeout just like any other type of event that is going to release a semaphore for the sake of a suspended routine. It can be a keyboard press, a timeout, or the union of these and several more events.

Therefore, I'd like to know the motivation for supporting these two states. They are reported in documentation and differentiated in APIs, therefore I assume there must be some good reason that I'm missing for them to exist.

Maybe timeout support from the OS ensures RTOSness responsivity, or maybe it guarantees 100% that something will wake up the task, which maybe is not so sure to happen if I had that timeout handled by the carefree hands of a userspace task.. ? Or maybe I'm completely misunderstanding everything at all.

I'd like to understand this aspect of FreeRTOS.

Thanks,
RM

RE: Difference between blocked and suspended

Posted by Westmoreland Engineering on May 21, 2013
Hello RM,

I haven't looked at the previous thread - but I will try to explain to you so this makes sense:

Think of vTaskSuspend ( NULL ); and vTaskResume ( xTaskHandle); as task control mechanisms. When the task is suspended vTaskSuspend ( NULL or xTaskHandle ) has been called.

When a task is waiting on an event - such as a semaphore being available or data from a Queue - and it waits - then it is blocking on that event. Think of this as task synchronization.

So you have two discrete things to think about regarding tasks - control and synchronization. Note these are simple examples but I am trying to get you to think about what you need to do with your tasks.

If you are new to the RTOS world - and it sounds like you are - it will take a little while to get your head around all of this. An RTOS will help you to distribute system resources in an equitable fashion, in either hard or soft real-time. You really need to understand what hard and soft real-time mean. I am sure you can find a lot of explanations of this on the internet.

The best way to learn is by doing - so the more you program and use the RTOS, the more you will learn. By the time you are done, you will understand the differences between blocked and suspended states; filling or waiting on queues, and giving and taking semaphores.

Hope This Helps,
John W.


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




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

Latest News

FreeRTOS kernel V10 is available for immediate download. Now MIT licensed.


FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

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