STM32 FreeRTOS Demonstrate access contention problems when using shared resources in a multitasking system

This exercise demonstrates the use of FreeRTOS on an STM32F401 microcontroller to implement priority-based preemptive multitasking. Two tasks control the blinking of a green and red LED, while a blue LED is used to indicate task interference during shared data access.

Features

• RTOS: FreeRTOS with priority-based preemptive scheduling.
• LED Control:
  • Green LED: Controlled by a task with normal priority.
  • Red LED: Controlled by a task with above-normal priority.
  • Blue LED: Indicates collisions in shared data access.
• Task Management: Demonstrates task scheduling, preemption, and shared resource handling.
• Collision Detection: Blue LED toggles when task interference occurs.

Hardware Requirements

• Microcontroller: STM32F401.
• LEDs:
  • Green LED: Connected to PA5.
  • Red LED: Connected to PB0.
  • Blue LED: Connected to PB7.
• Development Environment: STM32CubeIDE or compatible ARM GCC toolchain.

Software Requirements

• HAL Library: STM32 HAL library for GPIO and system initialization.
• FreeRTOS: Real-Time Operating System for multitasking.

Circuit Description

• Green LED: Connected to PA5 for visualizing the normal-priority task.
• Red LED: Connected to PB0 for visualizing the above-normal-priority task.
• Blue LED: Connected to PB7 for collision detection indication.
• Pull-down resistors are used for stabilization, with negative LED pins connected to ground.

How It Works

1. Green LED Task (Normal Priority)

• Toggles the green LED every 500 ms.
• Represents a lower-priority task, preempted by the Red LED Task when required.

2. Red LED Task (Above-Normal Priority)

• Toggles the red LED every 100 ms.
• Represents a higher-priority task that preempts the Green LED Task.

3. Collision Detection

• Both tasks access a shared variable start_flag.
• If a collision occurs, the Blue LED toggles to indicate interference.

4. Scheduler

• FreeRTOS kernel handles task scheduling.
• The Red LED Task preempts the Green LED Task due to its higher priority.
• The Blue LED highlights any collision during shared data access.

Steps to Run the Program

1. Setup STM32CubeMX

• Select the STM32F401 microcontroller.
• Enable GPIO pins for PA5, PB0, and PB7.
• Enable FreeRTOS middleware.

2. Configure Tasks

• Add two tasks:
  • FlashGreenLEDTask: Normal priority.
  • FlashRedLEDTask: Above-normal priority.

3. Generate Code

• Generate project code for STM32CubeIDE or your preferred IDE.

4. Build and Flash

• Build the project and flash it to the STM32F401 using an ST-Link or compatible programmer.

5. Observe Behavior

• The green LED toggles every 500 ms.
• The red LED toggles every 100 ms, preempting the Green LED Task.
• The blue LED toggles when a collision is detected during shared data access.

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Circuit Form

Demo Video

WhatsApp.Video.2024-12-03.at.20.02.10.mp4