nt-lite/code/kernel/ke_irq.c

// ke_irq.c - IRQ dispatch, kernel-side
#include <ke_irq.h>
#include <ke_sched.h>
#include <ke_irql.h>
#include <ke_dpc.h>
#include <hal_api.h>
#include <ke_debug.h>

#define MAX_IRQS 24
#define MAX_IRQ_HANDLERS 8

typedef struct IRQ_HANDLER_LIST {
    void (*Handlers[MAX_IRQ_HANDLERS])(void);
    uint8_t Count;
} IRQ_HANDLER_LIST;

static IRQ_HANDLER_LIST gIrqHandlers[MAX_IRQS];
static const HAL_API *gHal;
static volatile uint32_t gInterruptDepth = 0;

static KIRQL KiIrqToIrql(uint8_t irq) {
    KIRQL irql = (KIRQL)(DIRQL_BASE + irq);
    if (irql >= HIGH_LEVEL)
        irql = (KIRQL)(HIGH_LEVEL - 1);
    return irql;
}

void KeIrqInitialize(const HAL_API *hal) {
    gHal = hal;
}

__declspec(dllexport) void KeIrqRegister(uint8_t irq, void (*handler)(void)) {
    if (irq >= MAX_IRQS || !handler) return;

    IRQ_HANDLER_LIST* list = &gIrqHandlers[irq];
    for (uint8_t i = 0; i < list->Count; i++) {
        if (list->Handlers[i] == handler)
            return;
    }

    if (list->Count >= MAX_IRQ_HANDLERS) {
        DbgPrint("KeIrqRegister: IRQ %u handler table full\n", irq);
        return;
    }

    list->Handlers[list->Count++] = handler;
    gHal->Intc.RouteIrq(irq);
}

void KeIrqDispatch(uint8_t irq) {
    KIRQL targetIrql = KiIrqToIrql(irq);
    KIRQL currentIrql = KeGetCurrentIrql();

    // Do not ever lower IRQL on interrupt entry.  Nested IRQs are not expected
    // while IF is clear, but this keeps the software state sane if that changes
    // later.
    if (targetIrql < currentIrql)
        targetIrql = currentIrql;

    KIRQL oldIrql = KeRaiseIrql(targetIrql);

    if (irq < MAX_IRQS) {
        IRQ_HANDLER_LIST* list = &gIrqHandlers[irq];
        for (uint8_t i = 0; i < list->Count; i++) {
            if (list->Handlers[i])
                list->Handlers[i]();
        }
    }

    // Handlers are no longer allowed to context-switch directly.  Timer IRQs
    // only request rescheduling; KiExitInterrupt performs the switch after this
    // function returns, so the EOI is guaranteed to be sent first.  Keep the
    // software level at DIRQL until after the controller has been acknowledged.
    gHal->Intc.SendEoi();

    KeLowerIrql(oldIrql);
}

void KiEnterInterrupt(void) {
    gInterruptDepth++;
}

void KiExitInterrupt(void) {
    if (gInterruptDepth)
        gInterruptDepth--;

    // A reschedule is only legal after the interrupt unwound back to the
    // interrupted thread's original PASSIVE context.  If a future path ever
    // permits nested interrupting of DISPATCH/DIRQL code, leave the request
    // pending instead of switching while a spinlock/high-IRQL region is active.
    if (gInterruptDepth == 0 && KeGetCurrentIrql() == PASSIVE_LEVEL) {
        KiDrainDpcQueue();
        if (KeGetCurrentIrql() == PASSIVE_LEVEL)
            KiScheduleFromInterrupt();
    }
}