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Program the PIT for Precise Timing

hard3/8

Program the 8259 PIC for Interrupt Management Write a PS/2 Keyboard Interrupt Service Routine

Language

Compiler

2.0s Limit 256MB

Submit and pass all tests to enable saving to GitHub.

Implementation

Implement PIT timer programming in C.

Requirements:

Calculate divisors for different frequencies
Implement pit_set_frequency() with command byte and divisor
Implement timer ISR that increments ticks
Show elapsed time calculation
Implement simple task time slice decrement
Show timer command byte breakdown
Demonstrate frequency calculation
Show EOI being sent after timer interrupt
Calculate actual frequency from divisor

Test:

Show PIT programmed for 100 Hz
Show timer ticks incrementing
Show time slice decrement
Show elapsed time calculated
Show frequency math

Why This Matters

The command byte 0x36 and divisor math you compute here (1193182 / frequency) is exactly what Linux's early boot code and hobby kernels like those documented on the OSDev wiki use to get a reliable scheduler tick before the APIC timer or HPET is available. Off-by-one divisor errors here are why some early bootloaders drift out of sync with wall-clock time over long uptimes.

Hints

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Validation Suite

main.c

Workspace 1.0

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