What is a Watchdog? How to Use It on the BeagleBone?

Introduction

The Watchdog is a monitoring mechanism found in many computer systems, including the BeagleBone Black. Its main purpose is to monitor the system’s operation and take action in case of a malfunction or freeze.

The BeagleBone Black is a microcomputer based on an ARM processor. It is used in many embedded projects and can operate autonomously, for example in control or automation systems.

The BeagleBone Black’s Watchdog is an integrated hardware component that can be configured and activated through software. It is designed to continuously monitor the execution of the main program. If the Watchdog does not receive regular signals from the program, it interprets this as a malfunction or system freeze and takes action to address the issue.

The usefulness of the Watchdog lies in its ability to detect situations where the main program is no longer functioning correctly or has become unresponsive. This could include infinite loops, software crashes, hardware freezes, or other scenarios where the program stops responding.

When such a situation is detected, the Watchdog can take various actions depending on its configuration. For example, it may reboot the system, execute a recovery script, or generate an alert to report the incident.

Setting Up the Watchdog

We will now present two solutions for setting up the Watchdog on the BeagleBone Black. The Watchdog works with a specific file located in "" (path to be specified), which you must open and write a character to within 60 seconds. This allows the system to verify that the board is still functioning properly. Once the first character is written, the Watchdog is activated.

If no new character is written within 60 seconds, the board will automatically reboot.

This can be very useful, for example, if you have written a program and want the BeagleBone to reboot in case it crashes: simply open the Watchdog file from within your program. If your program crashes and stops writing to the file, the Watchdog will no longer receive signals, and the board will naturally reboot.

To set up the Watchdog, we will create a Bash script to activate it. To do this, open the terminal on the BeagleBone:

In the terminal, create a Bash file:

nano script_watchdog.script_watchdog

Here is the program to add to your Bash file:

#!/bin/bash
for (( ; ;))
do 
   cat > /dev/watchdog
done

You can then run this script with the following command:

./script_watchdog.sh

How to run the script at startup of the board?

To run the script at startup of the board, you need to add it to the “rc.local” file. Here is the command to run in the terminal:

sudo nano /etc/rc.local

Here’s what you need to add to the “rc.local” file to automate the program:

cd /home/debian/Desktop
./script_watchdog.sh

Include the Watchdog in Your Programs!

It can be very useful to include the Watchdog in your program to reboot your board if your program crashes.

To do this, simply open the Watchdog file inside your program. If your program crashes, the Watchdog file will no longer be open, and the board will naturally reboot.

Here’s an example of a function you can include in your Python program:

def watchdogs() : 
    fichier=open("/dev/watchdog","w")
    fichier.write("e")
    fichier.close()
watchdog()

Conclusion

In summary, the BeagleBone Black’s Watchdog is an essential monitoring mechanism that helps ensure the system’s reliability and availability. It is used to detect anomalies and freezes, and take appropriate actions to restore proper system functionality.