This repository centers around the rust binary project fand, whose main purpose is to run a control loop for a cooling fan on a Raspberry Pi 4. As such, the binary is oriented to this problem in particular, however future development should be oriented on making this a general lightweight control loop daemon.

On the other hand, this repository also contains library code which could in the future be spun up as its own crate to implement control loops in general. This will require some design work to better understand what a good API for potential users of the library might be. As it stands now, the API is very inflexible, unfriendly and quirky.

How to use

Compile it with cargo

cargo build --release

RaspberryPi 4 specific

To be able to use the PWM output (which is the default), one needs to follow the instructions here.

Running the binary

./fand --help

The binary can take a config file (see example) or use the default pipeline. To see all available operations and their parameters refer to either the documentation (which you can compile with cargo doc) or to parameter.rs.

Running with systemd

The intention of this software is to be run as a daemon; this is easy with systemd, simply create a fand.service file in /etc/systemd/system/ (or the corresponding directory in your distro) with the following contents:

[Unit]
Description=Fan speed controller daemon
ConditionPathExists=/path/to/fand
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=1
User=fand
ExecStart=/path/to/fand -s /tmp/fand.socket

[Install]
WantedBy=multi-user.target

Be sure to replace the path to fand, and if you don't need to use the unix socket (see below) you can remove the -s /path/to/socket part of the command.

Retrieving current state

This repo also contains two helper/debugging binaries, fan-cli and fan-get-out, which can be used to get the internal state of the control loop by connecting to a socket created by fand. The first of these two will print out all the internal updates of the different operations, while the second one will, when using the default configuration, print the current control loop output. You are welcome to check the code of these two binaries to possibly design your own to retrieve any piece of information you would want.