ClassicOS/pic.c

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

/* Small delay for older hardware bus timing */
static inline void io_wait(void) {
    outb(0x80, 0); 
}

void pic_init(void) {
    uint8_t a1, a2;

    // Save current masks
    a1 = inb(PIC1_DATA);
    a2 = inb(PIC2_DATA);

    // ICW1: Start initialization in cascade mode
    outb(PIC1_COMMAND, 0x11);
    io_wait();
    outb(PIC2_COMMAND, 0x11);
    io_wait();

    // ICW2: Master PIC vector offset
    outb(PIC1_DATA, PIC1_OFFSET);
    io_wait();
    // ICW2: Slave PIC vector offset
    outb(PIC2_DATA, PIC2_OFFSET);
    io_wait();

    // ICW3: Tell Master there is a slave at IRQ2 (0000 0100)
    outb(PIC1_DATA, 4);
    io_wait();
    // ICW3: Tell Slave its cascade identity (0000 0010)
    outb(PIC2_DATA, 2);
    io_wait();

    // ICW4: Set 8086/88 mode
    outb(PIC1_DATA, 0x01);
    io_wait();
    outb(PIC2_DATA, 0x01);
    io_wait();

    // Restore masks (or disable all to start clean)
    outb(PIC1_DATA, 0xFB); // Keep IRQ2 (cascade) open
    outb(PIC2_DATA, 0xFF);
}

void pic_send_eoi(uint8_t irq) {
    if (irq >= 8) {
        outb(PIC2_COMMAND, PIC_EOI);
    }
    outb(PIC1_COMMAND, PIC_EOI);
}

void pic_unmask(uint8_t irq) {
    uint16_t port;
    if (irq < 8) {
        port = PIC1_DATA;
    } else {
        port = PIC2_DATA;
        irq -= 8;
    }
    uint8_t value = inb(port) & ~(1 << irq);
    outb(port, value);
}

void pic_mask(uint8_t irq) {
    uint16_t port;
    if (irq < 8) {
        port = PIC1_DATA;
    } else {
        port = PIC2_DATA;
        irq -= 8;
    }
    uint8_t value = inb(port) | (1 << irq);
    outb(port, value);
}