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Program the PIT for Kernel Preemption

hard7/15

Program the 8259 Programmable Interrupt Controller Write a PS/2 Keyboard Driver

Language

Compiler

2.0s Limit 256MB

Submit and pass all tests to enable saving to GitHub.

Implementation

Implement PIT timer programming and scheduling simulation in C.

Requirements:

Define PIT ports (0x40 data, 0x43 command)
Implement pit_set_frequency() that calculates divisor and programs PIT
Show command byte (0x36) being sent
Show divisor split into low and high bytes
Implement timer_handler() that increments a tick counter
Simulate scheduler being called every N ticks
Show tick count and elapsed time
Implement a simple task structure with time_slice
Show preemption when time slice expires
Calculate and display actual frequency from divisor

Test:

Show PIT programmed for 100 Hz
Show timer ticks incrementing
Show scheduler called when time slice expires
Show elapsed milliseconds calculated from ticks

Why This Matters

Programming the 8253/8254 PIT at 100Hz is literally how the Linux kernel's early boot timer worked before the APIC timer and HPET took over, and it remains the simplest way any teaching kernel like xv6 implements preemptive multitasking. Get the frequency divisor calculation wrong and your entire scheduler's sense of elapsed time drifts, silently breaking any timeout logic built on top of it.

Hints

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Validation Suite

main.c

Workspace 1.0

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