Timer Subsystem

Time management and periodic interrupts

Overview

The timer subsystem manages clock events, time tracking, and task scheduling interrupts.

Timer Sources

PIT (Programmable Interval Timer)

Legacy timer using I/O ports 0x40-0x43
Provides periodic interrupts (IRQ 0)
Simple but slower frequency

APIC Timer

Modern local APIC timer
Per-CPU timer for better synchronization
Supports higher frequencies

Timer Functions

✓ System time tracking (uptime)
✓ Clock tick generation
✓ Context switch triggering
✓ Sleep/delay implementation
✓ Real-time deadline support

Key Takeaways

✓ Regular interrupts enable task switching
✓ Tracks system uptime and ticks
✓ Both PIT and APIC supported
✓ Enables sleep and delay functions
✓ Critical for real-time scheduling