FreeRTOS demo board

This project aims to design demo board for teaching principles of FreeRTOS. The demo board can be used i.e. during lectures for quick demonstration of basic features of FreeRTOS. The students can change parameters in order to see impact on system (i.e. change priority of task of semaphore given by timer). Insight to system is provided by UART and diodies indicating execution of tasks.

The part of project is creating tutorial explaining following aspects of FreeRTOS:

• Tasks
• Semaphores
• Queues
• Timers
• Project generation using CubeMX

First part of the tutorial will be observation of FreeRTOS feature on the demo board. The second part will be coding given functionality (using provided base- project).

Assumptions

Project based on Nucleo board with STM32F303RE microcontroller. Controlled and powered by host device via USB connection. FreeRTOS support provided via project generator CubeMX.

Functionalities

• task scheduling demonstration by switching diodes and sending commands by UART,
• configuration by UART interface,
• API for configuration on host device.

FreeRTOS features demonstrated

• Tasks
• Semaphores
• Queues
• Timers

Configuration Capabilities

• set duration time of each Task,
• set priority of each Task,
• give Semaphore,
• put value to Queue,
• start, stop and change period of software Timer,
• change Semphore given by timer.

There will be few semaphores, triggering both single and few tasks. Timer will be giving choosen semaphore.

FreeRTOS Architecture

Tasks

There are 3 Tasks defined for purpose of experimenting: myTask02, myTask03, myTask04. On start, each tasks turns on LED assigned to it. On exit, it turns off the diode. There is Task defined for purpose of communication: uartRX. It have the highest priority.

Semaphores

3 Semaphores are defined. Each Semaphore triggers each Task.

Semaphore	Taks triggered
myBinarySem01	myTask02
myBinarySem02	myTask03
myBinarySem03	myTask04

Sempahore code is passed do gs command to give specific group of semaphores. Please refer to table below.

Semaphore Code	Semaphores given
1	1
1	2
3	3
4	1, 2
5	2, 3
6	3, 1
7	1, 2, 3

Task uartRX is triggered via semaphore uartRX.

uartRX sempahore is set in UART Rx interrupt when there '\n' char detected.

Queue

One Queue is defined. It stores data sent by UART interface. Each Task tries to acquire data from Queue. If succeded, task sends processed data to UART via UartTX task.

Task	Data processing - f(x)
Task1	x*2
Task2	x*3
Task3	x*4

Software timers

Software timer gives chosen semaphore with set period to trigger specific tasks.

Parameters

Parameter	Function
taskX_duration	duration time in miliseconds for task X
taskX_proprity	priority of task X
timer_period	period of software timer in miliseconds
timer_given_semaphore	number of semaphore given by timer

API

Board can be programmed by sending UART commands defined in table below. General structure of command:

<command> <arg>

• arg - integer
• command - string

0 return value indicates status OK. -1 return value indicates that command was not found

Command	Parameter	Return value	Impact on system
cpt1	int	0, 1 - bad priority	change priority of Task1
cpt2	int	0, 1 - bad priority	change priority of Task2
cpt3	int	0, 1 - bad priority	change priority of Task3
cdt1	int	0, 3 - duration too small	change duration of Task1
cdt2	int	0, 3 - duration too small	change duration of Task2
cdt3	int	0, 3 - duration too small	change duration of Task3
sta_t	0	0	start Software Timer
sto_t	0	0	stop Software Timer
tp	int	0, 2- bad period	change period of Software Timer
ts	int [1-7]	0, 4 - bad semaphore number	change samephore given by timer
pq	int	0	put value to Queue
gs	int [1-7]	0, 4 - bad semaphore number	give choosen Semaphore

LED connection

Diode's cathodes should be connected to ground, while anodes to respective pins. Remember about current limiting resistor!

Task No	STM32 pin number
1	User diode / PA6
2	PB6
3	PA9

Literature

• Mastering The FreeRTOS
• CMSIS-RTOS API v2