Module pit

Support for legacy 8253-compatible timer.

This module implements support for the 8253 programmable interrupt timer, aka the “PIT”. This device provides a source of periodic interrupts that can be used for timing purposes.

The 8253 is rather old and has lots of quirks which are not found in more modern timer circuits. As a result, some amount of jitter/drift is unavoidable when using the PIT. Sadly this is unavoidable due to hardware limitation. For instance, the PIT’s internal frequency is a rational number but not an integer, so all calculations are imprecise due to integer rounding.

This implementation is based on guidance from the following sources:

• https://wiki.osdev.org/Programmable_Interval_Timer
• https://en.wikipedia.org/wiki/Intel_8253

Structs

Pit

Timer based on 8253 “PIT” hardware

PitFreq

Frequency of the PIT timer

Constants

RELOAD_1KHZ

Reload value corresponding to 1 KHz

Functions

reload_value

Computes a PIT reload value for the given frequency.