isr - Interrupt and IRQ dispatch

Header: kernel/include/kernel/isr.h
Source: kernel/arch/i386/isr.c
ASM stubs: kernel/arch/i386/isr_asm.S

Provides a thin, handler-table-based dispatch layer on top of the IDT. C code registers and unregisters callbacks for any interrupt vector; the ASM stubs push a unified register frame onto the stack and call the C dispatcher.

IRQ vector constants

Hardware IRQs are remapped by init_descriptor_tables() so that IRQ 0–15 occupy IDT vectors 32–47, well above the CPU exception range (0–31).

Data structures

registers_t

typedef struct registers {
    uint32_t ds;
    uint32_t edi, esi, ebp, esp, ebx, edx, ecx, eax;
    uint32_t int_no, err_code;
    uint32_t eip, cs, eflags, useresp, ss;
} registers_t;

Snapshot of CPU state at the moment an interrupt or exception fires. The ASM stubs push the processor-saved fields (eip, cs, eflags, useresp, ss) plus pusha output, ds, and the vector number / error code, then pass a pointer to this structure to the C handler.

Type aliases

typedef void (*isr_t)(registers_t);

Function-pointer type for interrupt callbacks. The handler receives a copy (not a pointer) of the register state at interrupt time.

Functions

init_isr_handlers

void init_isr_handlers(void);

Zero-initialise the 256-entry handler table. Called from init_descriptor_tables().

register_interrupt_handler

void register_interrupt_handler(uint8_t n, isr_t handler);

Install handler as the callback for vector n. Prints a confirmation message to the terminal and serial port. For IRQ vectors (n >= IRQ0) the message identifies the IRQ number; for exception vectors it identifies the interrupt number.

unregister_interrupt_handler

void unregister_interrupt_handler(uint8_t n);

Remove the callback for vector n by setting its slot to NULL.

is_registered

int is_registered(uint8_t n);

Return non-zero if a callback is currently registered for vector n.

Dispatch flow

Exceptions (vectors 0–31): If a handler is registered, it is called. Otherwise isr_handler calls PANIC("Unhandled Interrupt").

IRQs (vectors 32–47): If a handler is registered, it is called. Regardless of whether a handler ran, irq_handler sends an End-Of-Interrupt (EOI) signal to the master 8259 PIC (and also to the slave if the IRQ originated from the slave, i.e. vector ≥ 40).