MTE241 -Lab #3 - Solved

The goal of this lab is to familiarize you with the use of multiple execution threads (i.e. tasks).

 

Learning Objectives
 

After successfully completing this lab, you should be able to:

 

●     Create and use multiple threads of execution

●     Perform I/O with a number of peripheral devices simultaneously

 

Overview
 

This lab builds on the work you did in lab 3, and adds the additional requirement that you must use multiple concurrent tasks.

 

You’ll be using the Keil RTX5 real-time kernel. This is an implementation of the standard CMSIS RTOS2 interface, which is widely used in embedded systems. More information about the Keil RTOS2 implementation can be found at:

 https://www.keil.com/pack/doc/CMSIS/RTOS2/html/index.html

 

Implementing Multiple Threads
 

The purpose of a multi-tasking operating system is to allow several things to be done at the same time.

 

To use the multi-threading capabilities of the Keil RTX5, you need to enable that feature in the Run-Time Services. You also need to include the appropriate header file in your code:

 

#include <cmsis_os2.h> 

 

Each of your threads should be declared as follows:

 

void whatever(void *arg) { 

// ... your code in here ... 

}  

In RTOS2, each thread is just a function that takes one parameter and doesn’t return anything. The body of each thread will typically be an infinite loop, using something like while(1)​               or​           for(;;), and you must call some method in your loop that will allow the thread to give up​        control to the thread scheduler (e.g. osThreadYield()​              or ​ osDelay(), or waiting on a​   mutex).​

 

You will typically start your threads from your main()​               function. Somewhere in your ​               main()​  function you should have the following:

 

osKernelInitialize(); osThreadNew(whatever, NULL, NULL); osKernelStart(); 

 

The first function call initializes the RTOS kernel but does not start it.  At least one thread should be created before starting the kernel.  The first argument to osThreadNew ​       is the function that it​      will execute.  The second argument to osThreadNew ​   is the argument that will be passed to your​     function.  In this example it is NULL so no parameter is passed.  The third argument is a pointer to a structure that specifies the thread name, priority, and other attributes.  In this example it is NULL, so default attributes are used including priority osPriorityNormal​     .  The last function call​                starts the kernel and thread switcher.  It does not return unless an error occurs.