[RTOS Support] Take Semaphore before starting tasks

The FreeRTOS kernel is now an MIT licensed AWS open source project, and these pages are being updated accordingly.

Quality RTOS & Embedded Software

About Contact Support FAQ Download

Menu

Quick Start

Supported MCUs

PDF Books

Trace Tools

Ecosystem

Quick Start Guide

Support Forum

⇓ Download Source ⇓

FreeRTOS+ Ecosystem

FreeRTOS+TCP:
Thread safe TCP/IP stack

SafeRTOS:
TUV certified RTOS

OpenRTOS:
Commercial Licensed RTOS

Fail Safe File System:
Ensures data integrity

FreeRTOS BSPs:
3rd party driver packages

Trace & Visualisation:
Tracealyzer for FreeRTOS

CLI:
Command line interface

WolfSSL SSL / TLS:
Networking security protocols

RTOS Training:
Delivered online or on-site

IO:
read(), write(), ioctl() interface

FreeRTOS+ Lab Projects

FreeRTOS+POSIX:
POSIX threading API

FreeRTOS+FAT:
Thread aware file system

FreeRTOS Support Archive

The FreeRTOS support forum is used to obtain active support directly from Real Time Engineers Ltd. In return for using our top quality software and services for free, we request you play fair and do your bit to help others too! Sign up to receive notifications of new support topics then help where you can.

This is a read only archive of threads posted to the FreeRTOS support forum. The archive is updated every week, so will not always contain the very latest posts. Use these archive pages to search previous posts. Use the Live FreeRTOS Forum link to reply to a post, or start a new support thread.

[FreeRTOS Home] [Live FreeRTOS Forum] [FAQ] [Archive Top] [September 2014 Threads]

Take Semaphore before starting tasks

Posted by chaabanemalki on September 23, 2014

Hello, Since I started using FreeRTOS I had this weird behavior ( or it's normal). I create a semaphore (RxSemaphore), then i use this semaphore to block a task (Task0) with it. And another task (task1) to give RxSemaphore. When I run my code, Task0 takes RxSemaphore even if task1 didn't give RxSemaphore yet. The solution I use is to take RxSemaphore (xSemaphoreTake(RxSemaphore ,0);) in the first task that will run.

Is this a normal behavior or I'm missing something ?

Take Semaphore before starting tasks

Posted by rtel on September 23, 2014

That would depend on which function you were using to create the semaphore.

Regards.

Take Semaphore before starting tasks

Posted by chaabanemalki on September 23, 2014

I use only vSemaphoreCreateBinary(). Thank u

Take Semaphore before starting tasks

Posted by rtel on September 23, 2014

I use only vSemaphoreCreateBinary().

If you look at the vSemaphoreCreateBinary() macro you will see the initial state for the semaphore.

Assuming you are using a recent version of FreeRTOS it is recommended to use xSemaphoreCreateBinary() in place of vSemaphoreCreateBinary(). When using the 'x' function rather than the 'v' macro the semaphore will not be available until it has first been given.

Regards.