; retprobe.asm -- MINIMAL test of the DI return-PC trampoline, no drawing.
;
; Installs `entry` on the DI RAM stub (00000DB0h).  `entry` replaces the
; interrupt frame's saved PC with `ret_hook` and runs the stock handler.
; `ret_hook` bumps a marker and returns to the saved PC.  It deliberately does
; NOT preserve registers, so TCP liveness tells us whether the frame/PC dance
; itself is sound.  Scratch is in the payload's own page (01840800h).
;
; Linked at bit 01840000h by dwt/visual/build.sh.

	.text
_start:
	pushst
	dint
	setf	32, 0, 0
	movi	entry, a0, L
	move	a0, @00000DC0h, 0
	setf	16, 0, 0
	movi	0C080h, a0, L
	move	a0, @00000DB0h, 0
	sub	a0, a0
	move	a0, @01840800h, 0	; marker
	popst
	rets

entry:
	move	a0, @01840810h, 1
	setf	32, 0, 1
	move	*sp(020h), a0, 1
	move	a0, @01840804h, 1	; orig_pc
	movi	ret_hook, a0, L
	move	a0, *sp(020h), 1
	move	@01840810h, a0, 1
	jauc	3F7146D0h

ret_hook:
	move	@01840800h, a0, 0
	inc	a0
	move	a0, @01840800h, 0
	setf	32, 0, 1
	move	@01840804h, a0, 1	; orig_pc
	move	a0, -*sp, 1
	getst	a0			; (clobbers a0 on purpose)
	move	a0, -*sp, 1
	popst
	rets
	.end