Start working on rom-based kernel

kernel/intr.asm

@@ -0,0 +1,70 @@
+	; Get pointer to interrupt vector
+	; IN	al	number
+	; OUT	0:bx	ptr to vector
+intr_ptr:
+	xor bh, bh
+	mov bl, al
+	add bx, bx
+	add bx, bx
+	ret
+
+	; Set interrupt vector
+	; IN	al	number
+	;	ds:dx	ptr
+intr_set:
+	push bx
+	call intr_ptr
+	ss mov [bx], dx
+	ss mov [bx+2], ds
+	pop bx
+	ret
+
+	; Get interrupt vector
+	; IN	al	number
+	; OUT	es:bx	ptr
+intr_get:
+	call intr_ptr
+	ss mov es, [bx+2]
+	ss mov bx, [bx]
+	ret
+
+	; Save BIOS vectors
+	; Trashes ax, cx, bx, ds
+intr_backup:
+	mov cx, 0x20
+	xor bx, bx
+	mov ds, bx
+.loop:	; load segment
+	mov ax, [bx+2]
+	; skip transfer if not pointing to BIOS
+	cmp ax, 0xA000
+	jc .skip
+	; store segment
+	mov [bx+ivt2+2], ax
+	; copy offset
+	mov ax, [bx]
+	mov [bx+ivt2], ax
+	; iterate to next vector
+.skip:	add bx, 4
+	loop .loop
+	ret
+
+	; Restore BIOS vectors
+intr_restore:
+	mov cx, 0x20
+	xor bx, bx
+	mov ds, bx
+.loop:	; load segment
+	mov ax, [bx+ivt2+2]
+	; skip if not a vector to BIOS
+	cmp ax, 0xA000
+	jc .skip
+	; store segment
+	mov [bx+2], ax
+	; copy offset
+	mov ax, [bx+ivt2]
+	mov [bx], ax
+	; iterate to next vector
+.skip:	add bx, 4
+	loop .loop
+	ret