; blinkpc.asm -- resident blink that draws AFTER the stock display handler.
;
; Hook: the firmware's DI RAM trampoline at bit 00000DB0h
; (RLONG(0xFFFFFEA0) = 00000DB0h, stub `JA 3F7146D0h`).
;
;   entry    saves the interrupt's saved PC, replaces it with ret_hook, then
;            tail-jumps to the stock handler 3F7146D0h;
;   ret_hook runs when the stock handler `reti`s, draws the box, and returns
;            to the original PC with `rets 2` (the 2 skips the temporary a0
;            slot and keeps the interrupted stack balanced).
;
; Drawing after the handler matters: a draw before it is wiped by the handler's
; own screen work (measured: blink.asm counter runs, no box in any frame).
;
; Box: framebuffer (256,400), 64x64, white Terminal Manager body.
; State toggles every 0014h invocations (~20 frames at ~1 DI/frame idle).
;
; Linked at bit 01840000h by dwt/visual/build.sh.

	.text
_start:					; install, called by rdebug `jump`
	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	; counter
	move	a0, @01840810h, 0	; state (0 = black)
	popst
	rets

; ---- entry: point the interrupt's return at ret_hook, run stock handler ---
entry:
	move	a0, @01840860h, 1	; save interrupted a0
	setf	32, 0, 1
	move	*sp(020h), a0, 1	; saved PC (SP -> ST, +20h -> PC)
	move	a0, @01840820h, 1	; orig_pc
	movi	ret_hook, a0, L
	move	a0, *sp(020h), 1
	move	@01840860h, a0, 1
	jauc	3F7146D0h		; stock OS display handler

; ---- ret_hook: after the stock handler, draw, then resume -----------------
ret_hook:
	mmtm	sp, a0,a1,a2,a3,a4,a5	; field-independent A-reg save
	getst	a0
	setf	32, 0, 1
	move	a0, @01840840h, 1	; interrupted ST
	dint

	setf	16, 0, 0
	setf	32, 0, 1
	move	@01840800h, a0, 0
	inc	a0
	move	a0, @01840800h, 0
	cmpi	0014h, a0
	jrne	draw
	sub	a0, a0
	move	a0, @01840800h, 0
	move	@01840810h, a1, 0
	cmpi	0, a1
	jrne	was_white
	movk	1, a1
	jruc	set_state
was_white:
	sub	a1, a1
set_state:
	move	a1, @01840810h, 0

draw:
	move	@01840810h, a1, 0
	cmpi	0, a1
	jrne	pat_white
	sub	a2, a2
	jruc	pat_ready
pat_white:
	movi	0FFFFh, a2, L
pat_ready:
	movi	04064100h, a3, L
	movi	64, a4, L
	movi	4, a5, L
drow:
	move	a5, a1
dword:
	move	a2, *a3+, 0
	dsjs	a1, dword
	addi	03C0h, a3
	dsjs	a4, drow

	; restore the A registers (field 1 is still 32)
	mmfm	sp, a0,a1,a2,a3,a4,a5
	; leave with [ST][orig_pc] and the temporary a0 slot skipped by rets 2
	setf	32, 0, 1
	mmtm	sp, a0			; a0 slot at S-20h
	move	@01840820h, a0, 1	; orig_pc
	move	a0, -*sp, 1		; orig_pc at S-40h
	move	*sp(020h), a0, 1	; restore a0 from S-20h
	move	@01840840h, a0, 1	; interrupted ST (temporarily in a0)
	move	a0, -*sp, 1		; ST at S-60h
	move	*sp(040h), a0, 1	; restore a0 from S-20h
	popst				; restore interrupted ST/IE
	rets	2			; pop orig_pc, skip the a0 slot
	.end