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Nadir 8259 PIC driver

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Pierre-Emmanuel Gob. 2026-09-18 20:26:10 +02:00
parent 6ee1900c1a
commit b1b78bb5b9
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kernel/arch/x86_64/pic.c Normal file
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/* Nadir 8259 PIC driver: cascaded master/slave remap + EOI + masking.
*
* Runs in 64-bit long mode at Ring 0 (CPL 0) with the stage-2 GDT.
* Privileged instructions: `outb`/`inb` via io.h (trap #GP if CPL >
* IOPL); no `cli`/`sti`/`lidt`.
* Fault behavior: no CPU fault possible a wrong ICW order only
* misroutes IRQs.
*/
#include <stdint.h>
#include "io.h"
#include "pic.h"
/* Init control words: ICW1 starts init, ICW2 sets the vector base,
* ICW3 wires the cascade (master IRQ2 <-> slave identity 2), ICW4
* selects 8086 mode. io_wait() after each byte gives the slow 8259
* time to latch it. */
#define PIC_ICW1_INIT 0x11U
#define PIC_ICW3_MASTER_SLAVE_LINE 0x04U
#define PIC_ICW3_SLAVE_ID 0x02U
#define PIC_ICW4_8086 0x01U
void pic_remap(void)
{
/* WHY this exact order: the 8259 latches ICW2-4 only while in init
* mode, and the cascade identities must match or slave IRQs never
* reach the CPU. Mask-all at the end keeps devices quiet until
* their driver calls pic_unmask(). */
outb(PIC1_CMD, PIC_ICW1_INIT);
io_wait();
outb(PIC2_CMD, PIC_ICW1_INIT);
io_wait();
outb(PIC1_DATA, PIC_IRQ0_VECTOR);
io_wait();
outb(PIC2_DATA, PIC_IRQ8_VECTOR);
io_wait();
outb(PIC1_DATA, PIC_ICW3_MASTER_SLAVE_LINE);
io_wait();
outb(PIC2_DATA, PIC_ICW3_SLAVE_ID);
io_wait();
outb(PIC1_DATA, PIC_ICW4_8086);
io_wait();
outb(PIC2_DATA, PIC_ICW4_8086);
io_wait();
outb(PIC1_DATA, 0xFFU);
io_wait();
outb(PIC2_DATA, 0xFFU);
io_wait();
}
void pic_eoi(uint8_t irq)
{
if (irq >= PIC_IRQ_COUNT) {
return;
}
if (irq >= 8U) {
outb(PIC2_CMD, PIC_EOI);
}
outb(PIC1_CMD, PIC_EOI);
}
void pic_mask(uint8_t irq)
{
uint16_t port;
uint8_t mask;
if (irq >= PIC_IRQ_COUNT) {
return;
}
port = (irq < 8U) ? PIC1_DATA : PIC2_DATA;
mask = inb(port) | (uint8_t)(1U << (irq & 7U));
outb(port, mask);
}
void pic_unmask(uint8_t irq)
{
uint16_t port;
uint8_t mask;
if (irq >= PIC_IRQ_COUNT) {
return;
}
port = (irq < 8U) ? PIC1_DATA : PIC2_DATA;
mask = inb(port) & (uint8_t) ~(1U << (irq & 7U));
outb(port, mask);
}