Fan Service

ASUS laptops generally have a feature that lets the user toggle the fan speed. Fn-F5 on some models, Fn-F on others. The direct effect is to limit the fan speed, from whisper mode to megablast, and indirectly control performance. But it doesn’t work in OpenBSD, so I needed to write an ASUS ACPI WMI driver. acpi ACPI is a hardware abstraction layer that lets the computer tell the operating system how to do things. It provides functions in byte code which the OS interprets to perform certain tasks. So instead of having to write a driver for every CPU, you call the ACPI method _PSS and that tells you what to do. Of course, vendors want to include functionality that isn’t defined in the standard, so they add some extra methods, and then you end up writing some custom drivers anyway, for the little buttons that turn the microphone on and off, etc. OpenBSD (and other OSs) have lots of little drivers for ThinkPads and whatnot. ACPI method names are only four letters long, so what do we do ... Read full article.