pic.c

#include "io.h"
#include "pic.h"

/** pic_acknowledge:
 *  Acknowledges an interrupt from either PIC 1 or PIC 2.
 *
 *  @param num The number of the interrupt
 */
void pic_acknowledge(unsigned int interrupt){
    if (interrupt < PIC_1_OFFSET || interrupt > PIC_2_END) {
        return;
    }

    if (interrupt < PIC_2_OFFSET) {
        outb(PIC_1_COMMAND_PORT, PIC_ACKNOWLEDGE);
    } else {
        outb(PIC_2_COMMAND_PORT, PIC_ACKNOWLEDGE);
    }
}

void pic_remap(int offset1, int offset2){
    outb(PIC_1_COMMAND, PIC_ICW1_INIT + PIC_ICW1_ICW4);     // starts the initialization sequence (in cascade mode)
    outb(PIC_2_COMMAND, PIC_ICW1_INIT + PIC_ICW1_ICW4);
    outb(PIC_1_DATA, offset1);                              // ICW2: Master PIC vector offset
    outb(PIC_2_DATA, offset2);                              // ICW2: Slave PIC vector offset
    outb(PIC_1_DATA, 4);                                    // ICW3: tell Master PIC that there is a slave PIC at IRQ2 (0000 0100)
    outb(PIC_2_DATA, 2);                                    // ICW3: tell Slave PIC its cascade identity (0000 0010)

    outb(PIC_1_DATA, PIC_ICW4_8086);
    outb(PIC_2_DATA, PIC_ICW4_8086);

    // Setup Interrupt Mask Register (IMR)
    outb(PIC_1_DATA, 0xFD);                                 // 1111 1101 - Enable IRQ 1 only (keyboard).
    outb(PIC_2_DATA, 0xFF);

    asm("sti");                                             // Enable interrupts.
}