Does BIOS in Atom-32bit-intel board make IDT and GDT?

Question

I have Atom-32bit-intel board n450 with only BIOS in it, my goal is to use APIC timer and linke it with an ISR (0x21). After a while, I discoverd that IDT and GDT already exist(probably built by the BIOS) and no need to build them (the software is in C language and AT&T assembly):

        /*Read the IDTR*/
        sidt (idt_ptr)

        /*Read the GDTR*/
        sgdt (gdt_ptr)

So I tried just to use IDT's address to link my ISR to the IDT :

fill_interrupt(ISR_Nbr,(unsigned int) isr33, 0x08, 0x8E);

static void fill_interrupt(unsigned char num, unsigned int base, unsigned short sel, unsigned char flags)
{
    unsigned short *Interrupt_Address;

    /*address = idt_ptr.base + num * 8 byte*/
    Interrupt_Address = (unsigned short *)(idt_ptr.base + num*8);

    *(Interrupt_Address) = base&0xFFFF;
    *(Interrupt_Address+1) = sel;
    *(Interrupt_Address+2) = (flags>>8)&0xFF00;
    *(Interrupt_Address+3) = (base>>16)&0xFFFF;

}

When I try to call the ISR33 : int $0x21, the software crashes : SingleStep CPU[1] Error : Processor Running.

So where is it wrong ???

Remark: I use eclipse Heros(AT&T assembly), the code is in protected mode (CR0.PE = 1 I checked it, probably set by the BIOS).

Answer 1

Resolved :), as there is a BIOS, it already built the GDT/IDT, so I found there address using sidt and sgdt instructions, and i added my ISR to idt