; xtext.asm -- open a window on the live DWT X server and draw text in it.
;
; Run as a first-class process created by the COFF loader (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.
;
; This is xhello.asm plus the text path:
;   XLoadFont(d,"fixed")                   3FD4AE80
;   XCreateGC(d,win,mask,&values)          3F997000
;   XSetForeground(d,gc,1)                 3FD99A60
;   XMapWindow(d,win)                      3FD645B0
;   XSync(d,0) / XDrawString(...) loop     3FD9F6B0 / 3FDA0000
;
; The GC is created with a zero value-mask, so the server fills it from the
; screen's default GC (which carries the server's default font, "fixed").  The
; draw is repeated with an XSync between iterations so that it lands after the
; WM has framed/reparented/mapped the window; a single early draw can be lost
; when the window is reparented.
;
; 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
;
; The callee's `rets 2` pops the return address and the reserved slot, so SP is
; restored by the call itself; A14 is restored from that slot.  Do NOT keep the
; entry SP/A14 in RAM and restore them after each call: the app's own stack and
; Xlib data structures use the same free heap, and a clobbered saved-SP cell
; turns the next call into a wild push.  That exact pattern crashed the first
; version of this payload at XCreateGC.
;
; 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 the window/GC ids
; are kept in callee-saved registers (a11/a10/a12).
;
; Markers live in 224 bytes of zero padding at the end of .text (01842000h),
; NOT in the free heap: the first version's cells at 01895000h were overwritten
; by the OS heap (the string "Exiting\n" landed on them).
;
;   01842000  stage (1 start, 2 display, 3 window, 4 font, 5 GC, 6 setfg,
;                    7 map, 8 synced/drawn, 9 flushed, 0FFh failed)
;   01842020  display pointer
;   01842040  font id returned by XLoadFont
;   01842060  window id
;   01842080  GC id returned by XCreateGC
;   018420A0  XSetForeground return
;   018420C0  XMapWindow return
;   018420E0  last XSync return
;   01842100  first XDrawString return
;   01842120  second XDrawString return
;   01842140  final XSync return
;   01841760  strlen("0::0") -- must be 4
;
; Scratch: 01894000  argument area

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

	movi	1, a0, L
	move	a0, @01842000h, 1	; stage = 1

	; ---- convention check: strlen("0::0") == 4 --------------------
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	3FACE948h, a0, L	; ROM "0::0"
	move	a0, *a14+, 1		; arg0
	calla	3FB458D0h		; strlen
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, @01842160h, 1	; MARK strlen
	movi	4, a0, L
	cmp	a0, a8
	jrne	failed

	movi	2, a0, L
	move	a0, @01842000h, 1	; stage = 2

	; ---- display = XOpenDisplay("0::0") ---------------------------
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	3FACE948h, a0, L
	move	a0, *a14+, 1		; arg0 = name
	calla	3F9C2570h		; XOpenDisplay
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, a11			; Display * (callee-saved)
	move	a11, @01842020h, 1	; MARK display
	move	a11, a11
	jreq	failed

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

	movi	3, a0, L
	move	a0, @01842000h, 1	; stage = 3

	; ---- window = XCreateSimpleWindow(d,root,100,100,400,200,2,1,0) --
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	0, a0, L
	move	a0, *a14+, 1		; background = 0 (black)
	movi	1, a0, L
	move	a0, *a14+, 1		; border     = 1 (white)
	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
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, a10			; window id
	move	a10, @01842060h, 1	; MARK window
	move	a10, a10
	jreq	failed

	movi	4, a0, L
	move	a0, @01842000h, 1	; stage = 4

	; ---- font = XLoadFont(display, "fixed") -----------------------
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	FONTNAME, a0, L
	move	a0, *a14+, 1		; arg1 = name
	move	a11, *a14+, 1		; arg0 = display
	calla	3FD4AE80h		; XLoadFont
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, a9			; Font (callee-saved)
	move	a9, @01842040h, 1	; MARK font
	move	a9, a9
	jreq	failed

	movi	5, a0, L
	move	a0, @01842000h, 1	; stage = 5

	; ---- gc = XCreateGC(d, window, 0, NULL) ----------------------
	; mask 0 -> server default GC values (no value-list to misparse).
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	0, a0, L
	move	a0, *a14+, 1		; arg3 = values
	move	a0, *a14+, 1		; arg2 = mask 0
	move	a10, *a14+, 1		; arg1 = drawable
	move	a11, *a14+, 1		; arg0 = display
	calla	3F997000h		; XCreateGC
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, a12			; GC (callee-saved)
	move	a12, @01842080h, 1	; MARK gc
	move	a12, a12
	jreq	failed

	; ---- XSetForeground(display, gc, 1) --------------------------
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	1, a0, L
	move	a0, *a14+, 1		; arg2 = pixel 1 (white)
	move	a12, *a14+, 1		; arg1 = gc
	move	a11, *a14+, 1		; arg0 = display
	calla	3FD99A60h		; XSetForeground
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, @018420A0h, 1	; MARK setfg
	movi	6, a0, L
	move	a0, @01842000h, 1	; stage = 6

	; ---- XMapWindow(display, window) -----------------------------
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	move	a10, *a14+, 1		; window
	move	a11, *a14+, 1		; display
	calla	3FD645B0h		; XMapWindow
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, @018420C0h, 1	; MARK map
	movi	7, a0, L
	move	a0, @01842000h, 1	; stage = 7

	; ---- sync + draw, repeated: the WM needs time to frame/map -----
	movi	4, a9, L
draw_loop:
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	0, a0, L
	move	a0, *a14+, 1		; discard = 0
	move	a11, *a14+, 1		; display
	calla	3FD9F6B0h		; XSync (flush + round trip)
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, @018420E0h, 1	; MARK last sync

	; ---- XDrawString(display, window, gc, 20, 80, msg1, 12) ------
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	12, a0, L
	move	a0, *a14+, 1		; arg6 = length
	movi	MSG1, a0, L
	move	a0, *a14+, 1		; arg5 = string
	movi	80, a0, L
	move	a0, *a14+, 1		; arg4 = y
	movi	20, a0, L
	move	a0, *a14+, 1		; arg3 = x
	move	a12, *a14+, 1		; arg2 = gc
	move	a10, *a14+, 1		; arg1 = window
	move	a11, *a14+, 1		; arg0 = display
	calla	3FDA0000h		; XDrawString
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, @01842100h, 1	; MARK draw1

	; ---- XDrawString(display, window, gc, 20, 120, msg2, 10) ----
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	10, a0, L
	move	a0, *a14+, 1		; arg6 = length
	movi	MSG2, a0, L
	move	a0, *a14+, 1		; arg5 = string
	movi	120, a0, L
	move	a0, *a14+, 1		; arg4 = y
	movi	20, a0, L
	move	a0, *a14+, 1		; arg3 = x
	move	a12, *a14+, 1		; arg2 = gc
	move	a10, *a14+, 1		; arg1 = window
	move	a11, *a14+, 1		; arg0 = display
	calla	3FDA0000h		; XDrawString
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, @01842120h, 1	; MARK draw2

	; DSJS has a short range; trampoline to the long backward jump.
	dsjs	a9, draw_next
	jruc	draw_done
draw_next:
	jruc	draw_loop
draw_done:

	movi	8, a0, L
	move	a0, @01842000h, 1	; stage = 8

	; ---- final XSync flushes the last PolyText8 -----------------
	move	a14, -*sp, 1
	movi	01894000h, a14, L
	movi	0, a0, L
	move	a0, *a14+, 1		; discard = 0
	move	a11, *a14+, 1		; display
	calla	3FD9F6B0h		; XSync
	setf	16, 0, 0
	setf	32, 0, 1
	move	a8, @01842140h, 1	; MARK final sync

	movi	9, a0, L
	move	a0, @01842000h, 1	; stage = 9 (text drawn and flushed)
	jruc	done

failed:
	movi	0FFh, a0, L
	move	a0, @01842000h, 1

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

MSG1:	.byte	"HELLO VT1200", 0
MSG2:	.byte	"text works", 0
FONTNAME: .byte	"-DEC-Terminal-Medium-R-Normal--14-140-75-75-C-8-ISO8859-1", 0

	; 224 bytes of padding: marker cells 01842000h..0184217Fh live here.
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
	.end