# pihelp

**Repository Path**: mirrors_mkj/pihelp

## Basic Information

- **Project Name**: pihelp
- **Description**: A hardware watchdog for a Raspberry Pi using an AVR
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2020-09-25
- **Last Updated**: 2026-01-04

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

A hardware watchdog for a Raspberry Pi. It uses an atmega328 attached to the Raspberry Pi's
serial port, with a simple command line interface.

It will reset the Raspberry Pi if either a long or short watchdog timer isn't reset within 
a time period. It will also toggle a pin to alternate between booting to kernel\_emergency.img
and the normal kernel - see http://elinux.org/RPI_safe_mode . This makes it less risky to upgrading 
the boot image remotely. There are a few other features such as a bodgy random number generator
and hmac. The 'oneshot' watchdog lets you set a failsafe so that if you try something that doesn't work, it'l reboot after a set period of time.

A rough list of functionality is in the [read handler](main.c#L1134).

I implemented this to use with [PCextreme's](https://www.pcextreme.nl/) 
[Raspberry Colocation](http://raspberrycolocation.com/).

The system boots an initramfs as a bootloader with SSH - [Dropbear](https://github.com/mkj/dropbear) of course. I then boot the real kernel with [kexec](http://manpages.ubuntu.com/manpages/precise/man8/kexec.8.html) - that allows low-risk upgrades over the network.

![schematic](pihelp.png)