Start IVT handling, create debug IR as example user

debug.asm

@@ -1,5 +1,8 @@
+cpu 8086
+
 ; this kprints registers
-_int_2F:
+; expect to be called as interrupt routine
+debug_reg_ir:
   push ss
   push es
   push ds
@@ -30,4 +33,4 @@ _int_2F:
   pop ss
   iret
 .fmt:
-  db "AX=%X BX=%X CX=%X DX=%X SP=%X BP=%X SI=%X DI=%X", 0x0A, 0x0D, "DS=%X ES=%X SS=%X IP=%X CS=%X FL=%B", 0
+  db "AX=%X BX=%X CX=%X DX=%X SP=%X BP=%X SI=%X DI=%X", 0x0A, 0x0D, "DS=%X ES=%X SS=%X IP=%X CS=%X FL=%X", 0

intr.asm

@@ -0,0 +1,21 @@
+cpu 8086
+
+; set item in interrupt vector table
+; in:	bx	interrupt number
+;	ds:dx	new handler address
+ivt_set:
+  push es
+  push ax
+
+  xor ax,ax
+  mov es,ax
+
+  sal bx,1
+  sal bx,1
+
+  mov [es:bx], dx
+  mov [es:bx+2], ds
+
+  pop ax
+  pop es
+  ret

main.asm

@@ -40,24 +40,20 @@ _exit:
   db "Halted: Waiting for poweroff...", 0
 
 main:
-  mov ax,cs
-  mov ds,ax
+  mov ax, cs
+  mov ds, ax
 
-  sub sp, 0x30
+  mov bx, 0x002E
+  mov dx, debug_reg_ir
 
-  xor ax,ax
-  mov es,ax
-  mov ax,_int_2F
-  xchg ax,[es:0x2F*4]
-  mov ax,cs
-  xchg ax,[es:0x2F*4+2]
-  int 0x2F
-  test ax, 0xFF
-  int 0x2F
+  call ivt_set
 
-  add sp, 0x30
+  int 0x2E
+  cmp ax,0x55AA
+  int 0x2E
 
   ret
 
-%include "dumpreg.asm"
+%include "intr.asm"
+%include "debug.asm"
 %include "kprintf.asm"