Python script to allow you to control a usb watchdog
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__pycache__ Added threading, to run program in background Jul 31, 2018
LICENSE Initial commit Feb 1, 2018
README.md
requirements.txt Initial commit of the watchdog script Feb 1, 2018
usb watchdog.jpg Add files via upload Feb 2, 2018
watchdog.py Added threading, to run program in background Jul 31, 2018
watchdog.pyc Bug fix on reset, and change to python3 Jul 30, 2018

README.md

usb-watchdog

Original blogpost

What is it?

Python script to allow you to control a usb watchdog

How does it work?

These usb watchdogs that are available on ebay/aliexpress create a virtual serial port ( just like arduinos ) and they expect a heartbeat generated by some software. If that heartbeat is not received within a certain timeframe it will trigger its relays to shutdown and reset the computer. I've sniffed the serial port to reverse engineer the protocol which seems quite simple:

  • The USB watchdog expects you to send a number based on the corresponding ascii code. This number is the heartbeat threshold.
  • Thresholds are defined by numbers multiplied by 10. E.g. if you want to define a 10 second threshold for the heartbeat you should should send the ascii char that is equal to 1. For a 30 second threshold you should send the ascii char that is equal to 3.
  • Encode a character using its integer value as reference.
  • Sending char(255) forces a reset.
  • Sending char(128) returns information regarding status and firmware version (I'm too lazy to reverse this)

Everytime you send a heartbeat the usb watchdog saves its value and starts using it as reference. This means that if you want to change the threshold to 180 seconds, all you have to do is send a heartbeat the the ascii value that is equal to decimal 18.

Caveats

  • Avoid using very small thresholds. The last value that you sent to the usb watchdog will be used onwards. This means that if you set a threshold of 10 seconds and for some reason your computer gets reset you will then have 10 seconds to complete the boot process and start running this script again otherwise you might end up stuck in a loop.

Buy me a beer

If you find this script useful, buying me a beer would be much appreciated :)

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