pic.c

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#include "pic.h"
#include "io.h"
 
#define PIC1 0x20
#define PIC2 0xA0
 
void init_pic(void) {
    outb(PIC1,     0x11);  // starts the initialization sequence (in cascade mode)
    outb(PIC2,     0x11);
    outb(PIC1 + 1, 0x20);  // ICW2: Master PIC vector offset
    outb(PIC2 + 1, 0x28);  // ICW2: Slave PIC vector offset
    outb(PIC1 + 1, 4);     // ICW3: tell Master PIC that there is a slave PIC at IRQ2 (0000 0100)
    outb(PIC2 + 1, 2);     // ICW3: tell Slave PIC its cascade identity (0000 0010)
 
    outb(PIC1 + 1, 1);
    outb(PIC2 + 1, 1);
 
    // unmask IRQ0 / PIT, found in the wild as masked...
    uint8_t mask = inb(PIC1 + 1) & 0xFE;
    outb(PIC1 + 1, mask);
}
 
void pic_set_handled(int interrupt) {
    interrupt -= 0x20;
 
    outb(PIC1, 0x20);
    if(interrupt > 7) {
        outb(PIC2, 0x20);
    }
}