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A hardware watchdog for a Raspberry Pi using an AVR
C Assembly Makefile Python
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README.md

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.

I implemented this to use with PCextreme's Raspberry Colocation.

The system boots an initramfs as a bootloader with SSH - Dropbear of course. I then boot the real kernel with kexec - that allows low-risk upgrades over the network.

schematic

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