Hardware timers
This page describes supported hardware timers, for each architecture.
x86_64 and x86
| Name | Notes |
|---|---|
| PIT | Used only when the APIC is not present |
| RTC | Currently used for timekeeping. It shall later be replaced by something else and be used only as a fallback |
| APIC | Used to drive the scheduler |
| HPET | Used to calibrate the APIC timer |
The frequency of the APIC timer is not known, thus we need to calibrate it (determine its frequency). This is done at boot using the HPET.