ladybird/Kernel/PIC.cpp

#include "types.h"
#include "i386.h"
#include "IO.h"
#include "PIC.h"
#include "Assertions.h"

// The slave 8259 is connected to the master's IRQ2 line.
// This is really only to enhance clarity.
#define SLAVE_INDEX     2

#define PIC0_CTL        0x20
#define PIC0_CMD        0x21
#define PIC1_CTL        0xA0
#define PIC1_CMD        0xA1

#ifdef DEBUG_PIC
static bool initialized;
#endif

namespace PIC {

void disable(byte irq)
{
    byte imr;
    if (irq & 8) {
        imr = IO::in8(PIC1_CMD);
        imr |= 1 << (irq - 8);
        IO::out8(PIC1_CMD, imr);
    } else {
        imr = IO::in8(PIC0_CMD);
        imr |= 1 << irq;
        IO::out8(PIC0_CMD, imr);
    }
}

void enable(byte irq)
{
    byte imr;
    if (irq & 8) {
        imr = IO::in8(PIC1_CMD);
        imr &= ~(1 << (irq - 8));
        IO::out8(PIC1_CMD, imr);
    } else {
        imr = IO::in8(PIC0_CMD);
        imr &= ~(1 << irq);
        IO::out8(PIC0_CMD, imr);
    }
}

void eoi(byte irq)
{
    if (irq & 8)
        IO::out8(PIC1_CTL, 0x20);
    IO::out8(PIC0_CTL, 0x20);
}

void initialize()
{
#ifdef DEBUG_PIC
    ASSERT(!initialized);
#endif

    /* ICW1 (edge triggered mode, cascading controllers, expect ICW4) */
    IO::out8(PIC0_CTL, 0x11);
    IO::out8(PIC1_CTL, 0x11);

    /* ICW2 (upper 5 bits specify ISR indices, lower 3 idunno) */
    IO::out8(PIC0_CMD, IRQ_VECTOR_BASE);
    IO::out8(PIC1_CMD, IRQ_VECTOR_BASE + 0x08);

    /* ICW3 (configure master/slave relationship) */
    IO::out8(PIC0_CMD, 1 << SLAVE_INDEX);
    IO::out8(PIC1_CMD, SLAVE_INDEX);

    /* ICW4 (set x86 mode) */
    IO::out8(PIC0_CMD, 0x01);
    IO::out8(PIC1_CMD, 0x01 );

    // Mask -- start out with all IRQs disabled.
    IO::out8(PIC0_CMD, 0xff);
    IO::out8(PIC1_CMD, 0xff);

    // ...except IRQ2, since that's needed for the master to let through slave interrupts.
    enable(2);

    kprintf("PIC(i8259): cascading mode, vectors 0x%b-0x%b\n", IRQ_VECTOR_BASE, IRQ_VECTOR_BASE + 0x08);

#ifdef DEBUG_PIC
    initialized = true;
#endif
}

word get_isr()
{
    IO::out8(PIC0_CTL, 0x0b);
    IO::out8(PIC1_CTL, 0x0b);
    byte isr0 = IO::in8(PIC0_CTL);
    byte isr1 = IO::in8(PIC1_CTL);
    return (isr1 << 8) | isr0;
}

word get_irr()
{
    IO::out8(PIC0_CTL, 0x0a);
    IO::out8(PIC1_CTL, 0x0a);
    byte irr0 = IO::in8(PIC0_CTL);
    byte irr1 = IO::in8(PIC1_CTL);
    return (irr1 << 8) | irr0;
}

}