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;~~~~~~~~~~~~~other asm, dos stuff cut out so we dont' loose focus on the problem

jumpOffset:
    dd go_pm
    dw 0x08

; Offset address to our simple test interrupt
int_start :
   dd int_test
   dw 0x08

entry:
 
; Thanks from Brendan, as we have to make sure our GDTR points to the actual
; memory address, add code location and dos 0x100 onto our loaded offset 

    mov eax,0
    mov ax,cs
    shl eax,4
    add [gdtr+2],eax
    add [idtr+2],eax         ; set idtr and gdtr so it points to the 'real' address in memory
    add [jumpOffset],eax     ; do the same for our 32 pm addr

    add [int_start], eax     ; Set the value of int_start (our simple interrupt function) so
                             ; it has the "physical" address
    
    mov eax, [int_start]     ; Lets put this "physical" address value into our idt first address
    mov word [idt_start], ax ; word...so our idt interrupt 0 has the correct real address in 
                             ; physical memory
    

  cli          ; Clear or disable interrupts
  
  mov     al, 0x70
  mov     dx, 0x80
  out     dx, al      ; outb(0x80, 0x70) - disable NMI
          

  lgdt[gdtr]       ; Load GDT
  
  lidt[idtr]       ; Load IDT
     
  mov eax,cr0       ; The lsb of cr0 is the protected mode bit
  or al,0x01       ; Set protected mode bit
  mov cr0,eax       ; Mov modified word to the control register

jmp far dword [jumpOffset]  ;can't just use "jmp go_pm" as where in dos!

;                                 32 BIT
;---------------------------------------------------------------------------
[BITS 32]
go_pm :

mov ax, 0x10        ; use our datasel selector ( alternatively mov ax, datasel )
mov ds, ax,
mov es, ax
mov fs, ax
mov gs, ax

mov esp, 0fffffh    ; we need a simple stack if where calling functions!

mov word [es: 0xb8000],0x740 ; put a char to the screen!...yeahh!
                             ; Where all okay here :)

~ACCKKKK... REBOOTS !!!!!!!!!!!!!!!!!!!!!!!!!!
; Force a call to interrupt 0!
  Int 0x0           ; We call our interrupt 0 subroutine

; Do a divide by 0 error, so we force a call to our interrupt 0
;  mov eax, 0
;  mov ebx, 0
;  div ebx            ; eax divided by ebx, and stored back in eax


lp: jmp lp  ; loops here forever and ever...

;~~~~~~~other asm etc gdt values


align 4

; Our IDTR register value
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

idtr :
   dw idt_end - idt_start - 1  ; Length of the idt
   dd idt_start        ; physical address of idt


; This is the start of our idt - its actual value
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
align 4
idt_start:
   dw int_test         ; Address of our interrupt function
   dw 0x0008          ; selector
   db 0x00             ; control parameters
   db 0x86             ; access details
   dw 0x0              ; higher 16bits of our int address
idt_end:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

; Nothing special, just a very basic interrupt function so we know something
; has happened
;-------------------------------------------------------------------------
int_test:
pushad
push es

nop  ; just ignore.. :)  no operations
nop

mov ax,0x10
mov es,ax
mov byte [es: 0xb8004], "R" ; poke a character into the graphics output screen

pop es
popad
iret

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; interupt gate 00
   dw isr        ; (lower 16-bit offset) offset 0...15
   dw 0008h       ; code segment selector
   db 00000000b   ; reserved
   db 10001110b   ; P=1,dpl=00,0,d=1=32bit,xxx
   dw 0           ; offset 31...16

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    mov eax, [int_start]    ; Lets put this "physical" address value into our idt first address
    mov word [idt_start], ax ; word...so our idt interrupt 0 has the correct real address in 
                            ; physical memory

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    mov eax, [int_start]
    mov word [idt_start], ax
    shr eax,16
    mov word [idt_start+6], ax