; xhello.asm -- open a *new* X connection and create/map a window on the live
; DWT X server.
;
; Run as a first-class process created by xlaunch.asm (create_process), NOT in
; the rdebug dispatcher's context: a connect made from the rdebug process is
; accepted at the service layer but the server never reads the X11 setup, so
; XOpenDisplay returns an unusable Display.  A fresh process works.
;
; Calling convention (the one the firmware itself uses; see the WM at
; 07F57044 and the TM at 07E5D2B4):
;
;     MOVE  A14,-*SP,1        ; reserve the slot the callee restores A14 from
;     MOVI  argN,A0 / MOVE A0,*A14+,1   ; last argument first, upward via A14
;     ...
;     MOVI  arg0,A0 / MOVE A0,*A14+,1   ; first argument last
;     CALLA target
;
; Xlib clobbers the CPU's SETF field state, so the ABI's 32-bit field 1 is
; re-established after every call.  The Display pointer and root/window ids are
; kept in a11/a10 (both callee-saved by every Xlib entry point): a RAM cell can
; be overwritten by the new process's stack, a register cannot.
;
; Xlib entry points (Ghidra address -> bit address):
;   7F384AE XOpenDisplay(name)             -> 3F9C2570
;   7FA8372 XCreateSimpleWindow(...)       -> 3FD41B90
;   7FAC8B6 XMapWindow(display,window)     -> 3FD645B0
;   7FB3ED6 XSync(display,discard)         -> 3FD9F6B0
;   7F68B1A strlen(s)                      -> 3FB458D0   (convention check)
;
; Markers (32-bit cells, bit addresses; diagnostic only):
;   01890100  display pointer
;   01890110  root window
;   01890120  window id
;   01890130  XSync return
;   01890140  stage counter
;   01890160  strlen("0::0") -- must be 4; if not, we stop before touching Xlib

	.text
_start:
	setf	16, 0, 0
	setf	32, 0, 1
	mmtm	sp, a0,a1,a2,a3,a4,a5,a6,a7

	move	sp, @01890420h, 1	; entry SP
	move	a14, @01890400h, 1	; entry A14

	movi	1, a0, L
	move	a0, @01890140h, 1	; stage = 1

	; ---- convention check: strlen("0::0") == 4 --------------------
	move	a14, -*sp, 1
	movi	01892000h, a14, L
	movi	3FACE948h, a0, L	; ROM "0::0"
	move	a0, *a14+, 1		; arg0
	calla	3FB458D0h		; strlen
	move	@01890420h, sp, 1
	move	@01890400h, a14, 1
	setf	16, 0, 0		; Xlib leaves the field sizes changed;
	setf	32, 0, 1		; re-establish the ABI's 32-bit field 1
	move	a8, @01890160h, 1	; MARK strlen
	movi	4, a0, L
	cmp	a0, a8
	jrne	done

	movi	2, a0, L
	move	a0, @01890140h, 1

	; ---- display = XOpenDisplay("0::0") ---------------------------
	move	a14, -*sp, 1
	movi	01892000h, a14, L
	movi	3FACE948h, a0, L
	move	a0, *a14+, 1		; arg0 = name
	calla	3F9C2570h		; XOpenDisplay
	move	@01890420h, sp, 1
	move	@01890400h, a14, 1
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, a11			; keep the Display in a callee-saved reg
	move	a11, @01890100h, 1	; MARK display
	move	a11, a11
	jreq	done

	movi	3, a0, L
	move	a0, @01890140h, 1

	; ---- root = *(*(display+0x480)+0x40) --------------------------
	move	*a11(0480h), a10, 1
	move	*a10(040h), a10, 1
	move	a10, @01890110h, 1	; MARK root

	; ---- XCreateSimpleWindow(display,root,100,100,400,200,2,0,0) --
	move	a14, -*sp, 1
	movi	01892000h, a14, L
	movi	0, a0, L
	move	a0, *a14+, 1		; background = 0 (black)
	move	a0, *a14+, 1		; border     = 0
	movi	2, a0, L
	move	a0, *a14+, 1		; border width
	movi	200, a0, L
	move	a0, *a14+, 1		; height
	movi	400, a0, L
	move	a0, *a14+, 1		; width
	movi	100, a0, L
	move	a0, *a14+, 1		; y
	move	a0, *a14+, 1		; x
	move	a10, *a14+, 1		; parent = root
	move	a11, *a14+, 1		; display
	calla	3FD41B90h		; XCreateSimpleWindow
	move	@01890420h, sp, 1
	move	@01890400h, a14, 1
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, a10			; window id (root no longer needed)
	move	a10, @01890120h, 1	; MARK window

	movi	4, a0, L
	move	a0, @01890140h, 1

	; ---- XMapWindow(display, window) ------------------------------
	move	a14, -*sp, 1
	movi	01892000h, a14, L
	move	a10, *a14+, 1		; window
	move	a11, *a14+, 1		; display
	calla	3FD645B0h		; XMapWindow
	move	@01890420h, sp, 1
	move	@01890400h, a14, 1
	setf	16, 0, 0
	setf	32, 0, 1

	movi	5, a0, L
	move	a0, @01890140h, 1

	; ---- XSync(display, 0) ----------------------------------------
	move	a14, -*sp, 1
	movi	01892000h, a14, L
	movi	0, a0, L
	move	a0, *a14+, 1		; discard = 0
	move	a11, *a14+, 1		; display
	calla	3FD9F6B0h		; XSync
	move	@01890420h, sp, 1
	move	@01890400h, a14, 1
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, @01890130h, 1	; MARK sync

	movi	6, a0, L
	move	a0, @01890140h, 1

done:
	mmfm	sp, a0,a1,a2,a3,a4,a5,a6,a7
	movi	0, a8, L
	rets
	.end