rpi-battery-monitor | Monitor battery voltage from a Raspberry Pi

The ATtiny13 code is very simple and can be found in the avr/ directory. To get the tools in Debian:. Then run ./build-and-upload.sh. The script is configured to use an AVRISP mkII programmer over USB. If you have a different programmer, change the -c argument to avrdude. If you're using a different AVR microcontroller, e.g. an Arduino Uno, you will need to edit the script as well as make changes to the code in avr/monitor.c. For the RPi side of things, you can install the Rust toolchain on your RPi in the usual way. I've tested this with Raspbian jessie. You'll also need gcc, which is installed by default. The RPi is fairly slow; a clean build from scratch takes almost 40 seconds. I haven't tried cross-compiling from a more powerful system. Once you have built dependencies, a build takes only about 6 seconds. After you've installed the tools, you can build the code by running. in the root directory of this repository. You will get a binary at ./target/release/rpi-battery-monitor. Run it with no arguments to get a battery voltage reading.
Direct access to GPIO registers through /dev/mem
Realtime scheduler priority while reading data
rpi-battery-monitor can be used as a Munin plugin to get pretty graphs. The plugin must run as root, and the simplest way to accomplish this is by marking it setuid. This is a major security hazard because, although simple, this program has not been carefully audited for setuid safety. Thus I recommend you only do this on a single-user machine.