Watchdog Timer Use Cases

Table of Contents

• Description
• Code Components
• Simulation Components
• Observations and Discussion
• Reproducing the Results
• Dependency Installation
• Program Flow: Simplified Version
• Toolstack
• References
• Help
• Contribution
• License

Description

This project aims to implement the watchdog timer driver for the ATmega328p AVR and STM32f401xE microcontrollers and test its functionality using a blinking LED. The watchdog timer is a crucial safety feature available in many microcontrollers, designed to protect the system in case of a malfunction.

The watchdog timer operates like a countdown counter, starting from a specified value and decrementing towards zero. During normal operation, the system should reset the watchdog timer to its initial value at the end of each cycle. If the system fails to refresh the watchdog timer and it reaches zero, the watchdog timer will reset the system. This behavior indicates a potential malfunction that prevented the system from refreshing the watchdog timer.

The tests include a positive scenario where everything functions correctly and the system successfully refreshes the watchdog timer. Additionally, there are three negative scenarios discussed in the Observations and Discussion section, where the system fails to refresh the watchdog timer, triggering a reset to demonstrate the watchdog timer's protective mechanism.

Code Components

Pin Controller GPIO

This component includes two functions:

• GPIO_Init: This function only configures the pin that the LED is connected to as output.

• GPIO_Write: This function takes the preferred state of the LED, either ON (1) or OFF (0), and depending on it, it sets the LED pin to high or low.

LED State Manager LEDMgr

This component includes two functions:

• LEDM_Init: This function initializes the LED pin and sets its initial state.

  • It calls GPIO_Init to configure the LED pin as an output.
  • It sets the initial state of the LED to "High" by calling GPIO_Write, which writes a 1 to the LED pin bit position in the port data register.

• LEDM_Manage: This function is intended to be called repeatedly inside the super loop of the main function in main.c. It has two main responsibilities:

  • Toggling the LED state every 500ms.
  • Calling WDGM_AlivenessIndication each time it is executed to indicate the function's aliveness.

Watchdog Manager WDGM

This component includes four functions:

• WDGM_Init: This function initializes the internal variables of the Watchdog Manager, setting them to their initial values.

• WDGM_MainFunction: This function is called in the super loop of the main function in main.c. Every 100ms, it checks the call rate of the LEDM_Manage function to ensure it falls within a valid range. Ideally, LEDM_Manage should be called 10 times per 100ms. Due to possible delays in hardware components, it accepts a range of 8 to 12 calls per 100ms. If the call rate is within this range, it sets the global variable wdgmStatus to OK, indicating normal operation. Otherwise, it sets wdgmStatus to NOK, signaling a potential issue.

• WDGM_ProvideSupervisionStatus: This function returns the current status of the Watchdog Manager (wdgmStatus). It is used by the WDGDrv file to determine if the system is functioning normally or if there is a malfunction requiring a system reset.

• WDGM_AlivenessIndication: This function is called by LEDM_Manage each time it is executed. It increments a global counter that tracks the number of times LEDM_Manage has been called within the 100ms period.

Watchdog Driver WDGDrv

This component includes two main functions and one helper function that are needed for the Watchdog Driver:

• WDGDrv_Init: This function initializes the watchdog timer.

  • For ATmega328p AVR:

    • Sets the maximum timeout value to 64ms.
    • Activates the watchdog.
    • Optionally initializes another timer, depending on your implementation. This can be included here or in a separate function or source file.

  • For STM32F401xE:

    • Sets the maximum timeout value to 50ms.
    • Disables the window mode.
    • Enables the early interrupt feature.
    • Activates the watchdog.

• ISR(TIMER1_COMPA_vect): This is the Interrupt Service Routine (ISR) executed when Timer1 reaches the compare value (50ms). It calls the WDGDrv_IsrNotification function to handle the watchdog functionality.

• WDGDrv_IsrNotification: This function retrieves the status of the Watchdog Manager using WDGM_PovideSuppervisionStatus() and checks if the system is stuck in the WDGM_MainFunction. Based on this check:

  • If the status is OK and the system is not stuck (stuck_flag != 1), it refreshes the watchdog timer.
  • If the system is stuck, no action is taken, which allows the watchdog timer to expire and potentially reset the system.

Simulation Components

Observations and Discussion

Scenario A: Positive Scenario

In this scenario, the system works perfectly normally and refreshes the watchdog at the correct time.

Scenario B: Negative Scenario

In this scenario, we should comment the call of the WDGM_MainFunction function in the main function. We expect the watchdog timer to reset the system each 64ms.

Scenario C: Negative Scenario

In this scenario, we should comment the call of the WDGM_AlivenessIndication function in the LEDM_Manage function. we expect the watchdog timer to reset the system after 114ms.

Scenario D: Negative Scenario

In this scenario, we should decrease the periodicity of the call of the LEDM_Manage to be every 5ms. we expect the watchdog timer to reset the system after 114ms.

Reproducing the Results

1. Install ATmega328p: Follow the ATmega328p installation guide in the Dependency Installation section.
2. Import Project: Import the project from BlinkingLed_with_Watchdog into Eclipse IDE.
3. Rebuild Project: Rebuild the project in Eclipse.
4. Open Simulation: Open the simulation file in Proteus (preferably version 8.9).
5. Load Program File: In Proteus, ensure the .elf or .hex file is loaded in the Program File field by double-clicking the microcontroller.
6. Run Simulation: Start the simulation. By default, the code is set to the positive scenario.

To Reproduce Negative Scenarios:

• Option 1: Follow the above steps but open the specific scenario project in Eclipse. These projects are available here.
• Option 2: Edit the original project files to comment out the lines specified for each scenario. Rebuild the project in Eclipse and then run the simulation.

Dependency Installation

STM32F401xE Microcontroller

ATmega328p AVR Microcontroller

1. Install the AVR toolchain from here. Note that you should select AVR 8-Bit Toolchain depending on the operating system you are using.
2. Extract the downloaded zip folder to any preferable location.
3. Install the AVR plugin to Eclipse by following these steps:
   • From the Help menu, open Eclipse Marketplace.
   • Search for and install AVR Eclipse Plugin.
4. Before creating a project, remember to add the AVR paths to the system by following these steps.
   • From the Window menu, open Preferences.
   • From the right sidebar, open AVR then Paths.
   • Add the AVR GCC path by clicking the "Edit" button, changing the source to "Custom," and setting the "current value" to the bin folder of the toolchain you downloaded.
   • Add the AVR Header Files by making the same steps, but the "current value" will be set to the include folder nested in the avr folder of the toolchain.
   • Regarding the GNU make, you should first download the xpack build tools and then add the path to its bin folder in the "current value" field.

Program Flow: Simplified Version

• The program starts by initializing the LED pin and setting it to ON.
• Each 10ms, the LEDM_Manage is called. Inside this function,
  • The LED state only changes if 500ms has passed.
  • We call the WDGM_AlivenessIndication to keep a count of how many times the LEDM_Manage was called.
• Returning to the main function, each 20ms, the WDGM_MainFunction to make sure the system works fine and the LEDM_Manage is called at a normal rate (8-12 times per 100ms, ideally it should be 10 times per 100ms).
• In parallel, if 50ms are passed, the WDGDrv_IsrNotification is called. This function checks if the LEDM_Manage is called at a correct rate and the program didn't get stuck at any phase (specifically in the WDGM_MainFunction function). Depending on that check, either the system gets reset or the watchdog timer gets refreshed.

Toolstack

References

1. Atmel-7810-Automotive-Microcontrollers-ATmega328P_Datasheet
2. RM0368 Reference manual - STM32F401xB/C and STM32F401xD/E - advanced Arm®-based 32-bit MCUs

Help

As mentioned, the shown results are generated for the ATmega328p microcontroller. Understanding pin configuration and reading chapters 10, 14, and 15 of the datasheet shall set you going with exploring the project files. However, if you encounter any issues or have questions, feel free to reach out.

Contribution

Gratitude goes out to all team members for their valuable contributions to this project.

Kareem Noureddine	Nada Omran	Nouran Khattab	Mohamed Sami

License

All rights reserved © 2024 to Team 14 of the Embedded Systems Course - Systems & Biomedical Engineering, Cairo University (Class 2025).