idt.c

#include <stdint.h>
#include <string.h>                                                         // Include headers for int types and memset()

struct idt_entryStruct {                                                    // Struct for an entry into the IDT

    uint16_t    base1;                                                      // L.O. bits of ISR address
    uint16_t    select;                                                     // Code segment offset into the GDT
    uint8_t     always0;
    uint8_t     flags;                                                      // Flags specifying ring etc.
    uint16_t    base2;                                                      // H.O. bits of ISR address
} __attribute__((packed));


struct idtrStruct {                                                         // Struct for what will be loaded into idtr

    uint16_t    limit;                                                      // Size of the IDT
    uint32_t    base;                                                       // Base address of IDT
} __attribute__((packed));


struct idt_entryStruct idt[256];                                            // Let's have 256 entries
struct idtrStruct idtr;

void idt_setgate (uint8_t id, uint32_t base, uint16_t select, uint8_t flags) {  // Function to set ISRs, called by loadisr() in isr.c

    idt[id].base1   = (base & 0xffff);                                      // Get the L.O. bits of base address
    idt[id].select  = select;
    idt[id].always0 = 0;
    idt[id].flags   = flags;
    idt[id].base2   = (base >> 16) & 0xffff;                                // Get the H.O. bits of base address
}

void loadidt (void) {                                                       // Function to load an empty IDT, called by kernel

    idtr.limit  = (sizeof(struct idt_entryStruct) * 256) - 1;               // Size of our IDT - 1
    idtr.base   = (uint32_t) &idt;                                          // Base address. TODO: does this need a cast?

    memset (&idt, 0, sizeof(struct idt_entryStruct) * 256);                 // Clear out the IDT.

    extern void idt_init();                                                 // Call a function defined in asm to lidt our IDT
}