Article 1670 of comp.sys.handhelds:
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From: gson@niksula.hut.fi (Andreas Gustafsson)
Newsgroups: comp.sys.handhelds
Subject: Source code to CHIP-48 version 2.25
Message-ID: <1990Oct6.183603.29151@santra.uucp>
Date: 6 Oct 90 18:36:03 GMT
Sender: news@santra.uucp (Cnews - USENET news system)
Reply-To: gson@niksula.hut.fi (Andreas Gustafsson)
Organization: Helsinki University of Technology, Finland
Lines: 1567

Due to popular demand, I'm posting the complete source code for the
CHIP-48 video game interpreter to comp.sys.handhelds.  I hope this
will inspire others to write more free machine code software for the
HP48SX.

The intention of this posting is not that people should actually
assemble the code; it's much easier to get the binary which was
posted recently and is also available by FTP from vega.hut.fi as
/pub/misc/hp48sx/asap/chip48-2.25-bin.Z.  Rather, it should 
serve as a source of programming tips for those writing their own
machine code programs.

This source is written for the ASAP assembler, version 1.01.  ASAP is
also FTP:able from vega.hut.fi.  To run the assembler, you need a
32-bit Unix machine and Perl 3.0 which is available from most major
Unix archive sites.

Here it is.  Enjoy!
================================ Cut here ================================
; @(#) chip.asap 2.25 9/15/90
;
; chip.asap -- a CHIP-8 interpreter for the HP48SX
;
; (C) Copyright 1990 Andreas Gustafsson
;
;     Noncommercial distribution allowed, provided that this
;     copyright message is preserved, and any modified versions
;     are clearly marked as such.  
;
;     The program makes use of undocumented low-level features of
;     the HP48SX calculator, and may or may not cause loss of data,
;     excessive battery drainage, and/or damage to the calculator
;     hardware.  The Author takes no responsibility whatsoever for 
;     any damage caused by the use of this program.
;
;     THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
;     IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
;     WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
;

;
; Register usage:
;
; d0 = general pointing
; d1 = points to chip-8 instruction (physical)
;
; r0 = CHIP-8 I register
; r1 = last time value
; r2 = physical address of virtual zero
; r3 = CHIP-8 PC
;

; standard preamble for Kermit download
	data.b	'H'
	data.b	'P'
	data.b	'H'
	data.b	'P'
	data.b	'4'
	data.b	'8'
	data.b	'-'
	data.b	'A'
	data.a	#2dcc		; machine code object
begin:	data.a	end-begin	; length of object
; end of preamble


; HP48SX ROM locations
; These are for the Revision A ROM, they may need to be changed for
; other revisions.

	flush_kbd=#00d57	; flush keyboard buffer
	do_in_c=#01160		; perform "in.4 c" instruction
	alloc_str=#05b7d	; allocate string
	push_r0_shortint=#06537	; push r0 as short integer, restore regs
	save_rpl_regs=#0679b	; save d0, d1, b, d
	restore_rpl_regs=#067d2	; restore d0, d1, b, d
	check_1_arg=#18abf	; make sure stack isn't empty

; HP48SX RAM locations

	crcval=#00104		; hardware CRC register
	hwtimer=#00138		; hardware timer
	stackdisp_ptr=#7055B	; contains address of stack display
	menudisp_ptr=#70551	; contains address of menu display
	flags_37=#706ce		; flags -37 to -40

; data area layout (with a smarter assembler these offsets could be
; calculated automatically).
; Don't rearrange; in particular, the variables must be first and
; the order of the  "V10".."V15" pseudovariables is important.

	ofs_vars=0		; CHIP-8 variables, 16 vars * 2 nibbles = 32
	ofs_timer=32		; delay timer "V10", size = 2
	ofs_sound=34		; sound timer "V11", size = 2
	ofs_sndon=36		; sound on/off flag "V12.0", size = 1
	ofs_sdata=37		; speaker data "V12.1", "V13", size = 3
	ofs_ckeys=40		; control key status "V14-15", size=4
	ofs_csp=44		; CHIP-8 stack pointer, size 5
	ofs_cstack=49		; CHIP-8 stack, size "stacknibbles" = 64
	ofs_linetab=113		; display row table, size 64 * 5 = 320
	ofs_regsave=433		; r0..r3 temporary save location, size = 20
	ofs_end=453		; end of data area

; don't change these without updating the offsets above also
	
	stacklevels=16		; size of CHIP-8 stack
	stacknibbles=64		; 4*stacklevels

; execution begins here

	call.a	check_1_arg	; check that stack is not empty

	call.a	save_rpl_regs	; call ROM routine to save d0, d1, b, d

	; if flag -40 (clock display) is set, clear it and exit.
	; This is because the clock display interrupt (or whatever)
	; causes problems, and doesn't get turned off just by clearing
	; the flag.  However, it does get turned off when the screen is 
	; redrawn after we exit, so the next time this program is started
	; it will run normally.
	move.p5	flags_37,c
	move.a	c,d0		; point to flags -37..-40
	move.p	@d0,a		; get old flags
	brbc	3,a,noclock	; jump if flag -40 clear
	clrb	3,a		; clear flag -40
	move.p	a,@d0		; store updated flags
	jump.3	exit		; don't continue just yet
noclock:

	; allocate a string for temporary data storage

	clrb	#a,st		; no garbage collection done
	move.p5	ofs_end,c	; size of uninitialized data area
	call.a	alloc_str	; call ROM routine to allocate a string
	swap.a	c,d0
	move.a	c,r4		; now R4 points to the string

	; clear the CHIP-8 variables and initialize some pseudovariables

	move.a	c,d0		; point to variables (uses c value set above)
	clr.w	c
	move.w	c,@d0		; clear V0..V7
	add.a	16,d0
	move.w	c,@d0		; clear V8..VF
	add.a	16,d0
	move.p8	#40010000,c	; set timers to #00, sndon to #1,
				; and sdata to #400
	move.8	c,@d0

	; fill "linetab" with pointers to the display rows

	move.a	r4,a		; get start of data area
	move.p5	ofs_linetab,c
	add.a	a,c
	move.a	c,d0		; d0 points to linetab

	move.p5	stackdisp_ptr,c	; pointer to address of stack display
	move.p2	56,a		; 56 rows
	call.3	ltfill
	move.p5	menudisp_ptr,c	; pointer to address of menu display
	move.p2	8,a		; 8 rows
	call.3	ltfill

	; allocate a 4 kB string for the CHIP-8 virtual memory

	clrb	#a,st		; no garbage collection done
	move.p5	#2000,c		; 4 kB in nibbles
	call.a	alloc_str	; call ROM routine to allocate a string

	; now r0 points to the header of the newly allocated string 
	; object, and d0 points to the data part

	swap.a	d0,c
	move.a	c,r2		; virtual zero in r2

	; hate nondeterministic bugs...
	clr.w	a
	clr.w	b
	clr.w	c
	clr.w	d

chipmain:
	; copy the chip-8 program from the argument string to the virtual
	; chip-8 memory

	move.a	r2,a		; get virtual zero
	move.p5	#0400,c		; virtual #0200 bytes
	add.a	a,c
	move.a	c,d0		; now d0 points to virtual 0200

	move.a	@d1,c		; point to the argument object
	move.a	c,d1		; (presumably a string)
	move.a	@d1,a		; get the object type
	move.p5	#02a2c,c	; string type prefix
	brne.a	c,a,doerror	; exit if it isn't a string
	add.a	5,d1		; skip the type
	move.a	@d1,a		; get the object length
	sub.a	5,a		; subtract length of length
	move.p5	#01c00,c	; this is #1000 - #0200 bytes in nibbles
	brgt.a	c,a,nottoolong
doerror:
	jump.3	errexit		; string will not fit in 4 k
nottoolong:
	add.a	5,d1		; point to the object itself
	call.3	copynibbles

	; pop the argument string off the stack
	call.a	restore_rpl_regs
	add.a	5,d1
	inc.a	d
	call.a	save_rpl_regs

	; copy the hexadecimal character font to the virtual chip-8 memory,
	; unpacking it on-the-fly

	move.a	r2,c			; get virtual zero
	move.a	c,d0			; now d0 points to 0000 virtual
	move.a	pc,a
ref17:	move.p5	hexfont-ref17,c
	add.a	a,c
	move.a	c,d1			; now d1 points to the hex patterns
	move.p2	hexfontend-hexfont,a	; length (8 bits are enough)
fontcopylo:
	move.1	@d1,c			; read a nibble
	sln.a	c			; shift to high nibble in byte
	add.a	1,d1
	move.2	c,@d0			; store byte
	add.a	2,d0			
	dec.a	a
	brnz.b	a,fontcopylo

	intoff

; jump here when the "restart" key is pressed
restart:

	; initialize PC and I
	clr.a	c
	move.a	c,r0		; I=0000 in r0
	move.p3	#200,c		; relies on c being cleared
	move.a	c,r3		; PC=0200 in r3

	; initialize stack pointer

	move.a	r4,a		; get start of data area
	move.p5	ofs_csp,c
	add.a	a,c
	move.a	c,d0		; d0 now points to csp

	clr.a	c
	move.a	c,@d0		; csp cleared

	call.3	i00e0		; erase display

	; initialize the time value

	clr.a	c		; must clear all of c for comparison below
	move.p3	hwtimer,c
	move.a	c,d0		; point to hardware timer
	move.a	@d0,c
retry1:	move.a	c,a
	move.a	@d0,c
	brne.a	c,a,retry1	; loop until we get same value twice

	move.p5	#00F80,a	; mask away 7 low bits of time value
	and.a	a,c
	move.a	a,r1

nextinstr:
	call.3	realtime	; do real-time chores
	brcc	nocarry
rtcarry:
	brbs	4,a,restart	; ENTER was pressed
	; otherwise, the abort key was pressed; make a clean exit

exit:
	call.a	restore_rpl_regs

	move.a	@d0,a		; dispatch next RPL instruction
	add.a	5,d0
	jump.a	@a

nocarry:
	; There appears to be some kind of interrupt that 
	; checks the keyboard status, and that doesn't get
	; turned off by "intoff".  Not knowing how to turn it off, we
	; try to live with it by flushing the keyboard buffer ever so
	; often, and trying to keep the "out" register zeroed most of
	; the time (so that the keyboard will appear inactive when
	; the interrupt checks it, even if keys really are being pressed).

	intoff			; just in case someone turned them on again

	call.a	flush_kbd	; flush keyboard buffer (trashes d1 and c)

dispatch:
	; dispatch a CHIP-8 instruction
	move.a	r3,c	; get cpc
	move.a	c,a	; keep unincremented value
	add.a	2,a	; increment cpc by 2 bytes
	move.a	a,r3	; store incremented cpc
	call.3	virtophy ; unincremented value is in c
	move.a	c,d1	; store virtual pc in d1

	clr.a 	c
	add.a	1,d1	; point to MSN
	move.p	@d1,c	; get MSN of first byte of CHIP-8 instruction
	sub.a	1,d1	; back to beginning of instruction
	add.a	c,c
	add.a	c,c	; now c = nibble * 4

	move.a	pc,a
ref6:	add.a	c,a
	move.p5	jumptab-ref6,c
	add.a	a,c	; now c = jumptab + nibble * 4
	move.a	c,d0
	clr.a	c	; clear the 5th nibble
	move.4	@d0,c	; now c = jumptab entry

	move.a	pc,a
jtref:	add.a	c,a	; now a = jump address

	move.a 	pc,c
retref:	add.a	retloc-retref,c
	push.a	c	; push return address on stack
	jump.a	a	; jump to instruction routine

retloc:
	brcs	errexit	; if carry is set, an error has occurred
	jump.3	nextinstr

errexit:	
	move.w	r3,c		; get the current CHIP-8 PC value
	move.w	c,r0		; move to R0
	call.a	push_r0_shortint ; ROM routine: push short integer from R0
				; (this also restores saved d0, d1, b, d)
	call.a	save_rpl_regs	; save the registers again (redundant?)
	jump.3	exit


; ltfill -- fill a part of "linetab"
ltfill:
	move.a	c,d1
	move.a	@d1,c	; get display address
	add.a	16,c	; increment past the GROB header (20 nibbles)
	add.a	4,c
ltfill_loop:
	move.a	c,@d0
	add.a	16,c	; increment to next row (34 nibbles)
	add.a	16,c	
	add.a	2,c
	add.a	5,d0
	dec.b	a
	brnz.b	a,ltfill_loop
	ret


; copynibbles -- copy a memory block
;
; d1 points to source, d0 to destination, and 
; a contains the number of nibbles to copy
copynibbles:
copylo:
	brz.a	a,copyend
	move.1	@d1,c
	move.1	c,@d0
	add.a	1,d0
	add.a	1,d1
	dec.a	a
	jump.3	copylo
copyend:
	ret

; realtime -- do various timer-driven real-time processing
;
; In: nothing
; Out: carry set iff real-time keypress detected; key code is in a
; Uses: all 16 nibbles of a and c; d0
;       but neither b nor d
;
realtime:

	; flip the speaker if the sound is on
	call.3	soundpd0	; point to sound timer
	move.b	@d0,c
	brz.b	c,silent
	add.a	2,d0		; point to sound on/off flag
	move.p	@d0,c
	brz.p	c,silent
	add.a	1,d0		; point to speaker data
	move.3	@d0,c
	out.x	c
	not.x	c	; turn #400 into #800 and vice versa
	move.p3	#c00,a
	and.x	a,c
	move.3	c,@d0
silent:

	; check the hardware timer register to see if it is time for
	; a 64 Hz realtime clock tick

	clr.a	c		; must clear all of c for comparison below
	move.p3	hwtimer,c
	move.a	c,d0
	move.a	@d0,c
retry2:	move.a	c,a
	move.a	@d0,c
	brne.a	c,a,retry2	; loop until we get same value twice

	move.p5	#00F80,a	; mask away 7 low bits of time value
	and.a	a,c

	move.a	r1,a		; now a is old value, c is new value
	brne.a	c,a,dotick
	jump.3	notick		; code at notick depends on c.0 being zero

dotick:	; handle a 64 Hz tick

	clr.a	c		; decrement r1 by #80
	move.p2	#80,c
	sub.a	c,a
	move.p5	#00F80,c	; mask 
	and.a	c,a
	move.a	a,r1

	call.3	timerpd0	; point to delay timer
	move.b	@d0,c
	brz.b	c,timerzero
	dec.b	c
	move.b	c,@d0
timerzero:

	add.a	2,d0		; point to sound timer
	move.b	@d0,c
	brz.b	c,soundzero
	dec.b	c
	move.b	c,@d0
soundzero:

	; check for various control keys

	call.3	ckeyspd0	; point d0 to key status

	move.p3	#010,c		; row ENTER..backstep
	out.x	c
	call.a	do_in_c
	move.a	c,a		; save "in" data in a
	clr.a	c
	out.x	c		; zero "out" port as fast as possible

	move.4	@d0,c		; get previous key status
	move.4	a,@d0		; save current key status
	not.a	a		; get keys that are not pressed
	and.a	c,a		; ..but were..
	retbs	4,a		; return with carry set if ENTER pressed
	retbs	0,a		; same for the backstep key
	brbs	3,a,togglesound	; +/-
noabort:
	move.p1	#1,c	; set flag to indicate that a tick took place
notick:	
	retclrc		; return tick flag in c.0


; toggle the sound flag (this is jumped to when the +/- key is pressed)
togglesound:
	call.3	sndonpd0
	move.p	@d0,c
	not.a	c
	move.p1	#1,a
	and.a	a,c
	move.p	c,@d0
	jump.3	noabort
	

; nnnc - get NNN field of current instruction to c register
;
; In:	d1 pointing to chip-8 instruction
; Out:	NNN field of instruction in c (5 valid nibbles)
; Uses: none
nnnc:
	clr.a 	c	; clear nibbles 3..4
	move.1	2,p
	move.p	@d1,c	; set nibble 2
	move.1	0,p
	add.a	2,d1	; point to second byte of instruction
	move.b	@d1,c	; set nibbles 0 and 1
	sub.a	2,d1	; restore d1
	ret


; virtophy -- convert virtual address to physical address
;
; In:   virtual address in c
; Out:  physical address in c
; Uses: a
virtophy:
	add.a	c,c	; convert bytes to nibbles
	move.a	r2,a	; convert virtual to physical
	add.a	a,c
	ret


; varpd0 - get pointer to variable to d0
; 
; In:	d1 points to nibble containing variable number
; Out:	d0 points to variable
; Uses: a,c
varpd0:
	clr.a 	c
	move.p	@d1,c	; get nibble with variable number
cvarpd0:
	add.a	c,c	; convert bytes to nibbles
	move.a	r4,a
	add.a	a,c
	move.a	c,d0
	ret


; var0pd0 -- load d0 with pointer to V0
;
; In:	none
; Out:	d0 points to variable 0
; Uses: a,c
var0pd0:
	clr.a 	c
	move.p1	#0,c
	jump.3	cvarpd0


; varfpd0 -- load d0 with pointer to VF
;
; In:	none
; Out:	d0 points to variable F
; Uses: a,c
varfpd0:
	clr.a 	c
	move.p1	#f,c
	jump.3	cvarpd0

timerpd0:
	clr.a	c
	move.p2	#10,c
	jump.3	cvarpd0	; point d0 to timer

soundpd0:
	clr.a	c
	move.p2	#11,c
	jump.3	cvarpd0	; point d0 to sound timer

sndonpd0:
	clr.a	c
	move.p2	#12,c
	jump.3	cvarpd0	; point d0 to sound on/off flag

ckeyspd0:
	clr.a	c
	move.p2	#14,c
	jump.3	cvarpd0	; point d0 to control key status


; varxcvarya -- get values of X and Y variables
; In:	d1 points to instruction
; Out:	c contains VX, zero padded to .a field
;	a contains VY, zero padded to .a field
; Uses:	d0
varxcvarya:
	call.3	varpd0	; get pointer to X
	clr.a	c
	move.b	@d0,c	; get X value
	push.a	c
	add.a	3,d1	; point to Y nibble in instruction
	call.3	varpd0	; get pointer to Y
	clr.a	a
	move.b	@d0,a	; get Y value
	pop.a	c
	sub.a	3,d1	; back to beginning of instruction
	ret


; In:	d1 points to beginning instruction
; Out:	c contains VX (5 nibbles valid)
;	a contains VY (5 nibbles valid)
;	d0 points to VX
; Uses: none
alusetup:
	add.a	3,d1	; point to Y nibble in instruction
	call.3	varpd0
	sub.a	3,d1
	clr.a	c
	move.2	@d0,c	; VY in c
	push.a	c
	call.3	varpd0	; d0 is pointer to VX
	clr.a	a
	move.2	@d0,a	; VX in a
	pop.a	c	; VY in c
	swap.a	a,c	; now VX in c and VY in a
	ret

savecarry:
	srn.a	c	; extract the carry byte
	srn.a	c
lsbcarry:
	move.p2	#01,a	; use low bit only
	and.b	a,c		
	push.a	c
	call.3	varfpd0	; get a pointer to VF
	pop.a	c
	move.b	c,@d0	; store the carry byte
	retclrc


; testkey -- check whether a given hex key is pressed
;
; In: key number in c (5 low nibbles must be valid)
; Out: low nibble of c is nonzero iff key is pressed
; Uses: a,d0
testkey:
	add.a	c,c	; index into keytab
	move.a	pc,a
ref16:	add.a	c,a
	move.p5	keytab-ref16,c
	add.a	a,c
	move.a	c,d0	; now d0 points to keytab
	clr.a	c
	move.1	@d0,c	; get "out" data
	out.x	c
	call.a	do_in_c
	move.a	c,a	; store the input value in a
	clr.a	c
	out.x	c	; zero "out" port as fast as possible
	add.a	1,d0
	move.1	@d0,c	; get "in" mask
	and.a	a,c
	ret

; setup subroutine for fx55 or fx65 instruction
;
; In: d0 points to VX
; Out: d0 points to to V0, a points to VX, and d1 points to MI
varcopysetup:
	swap.a	c,d0		; copy d0 to c
	move.a	c,d0
	push.a	c		; save pointer to the last variable
	call.3	var0pd0		; point d0 to first variable (v0)
	move.a	r0,c		; get I
	call.3	virtophy
	move.a	c,d1		; point d1 to data at I
	pop.a	c
	move.a	c,a		; now a contains pointer to last var.
	ret


i0:	; mcode call 
	call.3	nnnc
	move.a	c,a	; routine address is now in a
	clr.a	c
	move.p2	#e0,c
	breq.a	c,a,i00e0
	move.p2	#ee,c
	breq.a	c,a,i00ee
	retsetc		; illegal mcode call

i00e0:	; erase screen
	move.a	r4,a		; get start of data area
	move.p5	ofs_linetab,c
	add.a	c,a

	; a contains linetab pointer
	; b counts down from 64
	move.p2	64,c
	move.a	c,b
eraselo:
	move.a	a,d0
	move.a	@d0,c
	move.a	c,d0	; d0 now points to display memory
	clr.w	c
	move.w	c,@d0	; erase 16 nibbles
	add.a	16,d0
	move.w	c,@d0	; and 16 more
	add.a	16,d0
	move.b	c,@d0	; and 2 more, total 34
	add.a	5,a
	dec.b	b
	brnz.b	b,eraselo
	retclrc

		
i00ee:	; subroutine return
	move.a	r4,a		; get start of data area
	move.p5	ofs_csp,c
	add.a	a,c
	move.a	c,d0	; c and d0 both point to csp
	move.a	@d0,a	; now a contains the chip-8 stack pointer (0..4n-4)
	retz.a	a	; return with carry set if stack underflow
	sub.a	4,a	; drop one level
	move.a	a,@d0	; save new csp
	add.a	5,c	; point c at stack[0]
	add.a	a,c	; point c at popped level
	move.a	c,d0	; point d0 at popped level
	clr.a	c
	move.4	@d0,c
	move.a	c,r3	; set pc
	retclrc

i1:	; 1NNN, jump
dojmp:	call.3	nnnc
	move.a	c,r3	; assign to pc
	retclrc

i2:	; 2NNN, subroutine call
	move.a	r4,a	; get start of data area
	move.p5	ofs_csp,c
	add.a	a,c

	move.a	c,d0	; d0 and c both point to csp
	move.a	@d0,a	; now a contains the chip-8 stack pointer (0..4n-4)
			; c still points at csp
	add.a	5,c	; point c at stack[0]
	add.a	a,c	; point c at first free stack level
	swap.a	c,d0	; now d0 points to free stack and c points to csp
	move.a	r3,a	; get pc
	move.4	a,@d0	; store pc in stack
	swap.a	c,d0	; now d0 points to cpc again
	move.a	@d0,a	; now a contains the chip-8 stack pointer (0..4n-4)
	add.a	4,a
	move.p5	stacknibbles,c
	retlt.a	c,a	; return with carry set if stack overflow
	move.a	a,@d0	; store incremented sp
	jump.3	dojmp	; the reset is like 1nnn


i3:	; 3XKK, skip if X==KK
	call.3	varpd0	; get pointer to X
	add.a	2,d1	; point to second byte of instruction
	move.b	@d1,a	; now a = KK
	move.b	@d0,c	; now c = VX
skipeq:
	brne.b	c,a,noskip
doskip:	swap.a	c,r3	; increment cpc by 2
	add.a	2,c
	swap.a	c,r3
noskip:
	retclrc

i4:	; 4XKK, skip if X<>KK
	call.3	varpd0	; get pointer to X
	add.a	2,d1	; point to second byte of instruction
	move.b	@d1,a	; now a = KK
	move.b	@d0,c	; now c = VX
skipne:
	breq.b	c,a,noskip
	jump.3	doskip

i5:	; 5XY0, skip if X==Y
	call.3	varxcvarya	; get VX to c, VY to a
	jump.3	skipeq

i9:	; 9XY0, skip if X!=Y
	call.3	varxcvarya	; get VX to c, VY to a
	jump.3	skipne

i6:	; 6XKK, load variable by constant
	call.3	varpd0	; get pointer to X
	add.a	2,d1	; point to second byte of instruction
	move.b	@d1,a	; now a = KK
	move.b	a,@d0	; store in variable
	retclrc

i7:	; 7XKK, add constant to variable
	call.3	varpd0	; get pointer to X
	add.a	2,d1	; point to second byte of instruction
	move.b	@d1,a	; now a = KK
	move.b	@d0,c	; get old value
	add.b	a,c	; add KK
	move.b	c,@d0	; store new value
	retclrc


i8:	; arithmetic and logic operations
	add.a	2,d1	; point to last nibble of instruction
	move.1	@d1,a
	sub.a	2,d1

	move.p1	#0,c
	brne.p	c,a,noti8xy0
i8xy0:	; VX := VY
	call.3	alusetup
	move.b	a,@d0	; store result
	retclrc
noti8xy0:

	move.p1	#1,c
	brne.p	c,a,noti8xy1
i8xy1:	; VX := VX or VY
	call.3	alusetup
	or.b	a,c
	move.2	c,@d0	; store result
	retclrc
noti8xy1:

	move.p1	#2,c
	brne.p	c,a,noti8xy2
i8xy2:	; VX := VX and VY
	call.3	alusetup
	and.b	a,c
	move.2	c,@d0	; store result
	retclrc
noti8xy2:

	move.p1	#3,c
	brne.p	c,a,noti8xy3
i8xy3:	; VX := VX xor VY
	call.3	alusetup
	move.b	a,b
	or.b	c,b	; (x or y) in b
	and.b	a,c	; (x and y) in c
	not.b	c	
	and.b	b,c	; (x xor y) in c
	move.b	c,@d0	; store result
	retclrc
noti8xy3:

	move.p1	#4,c
	brne.p	c,a,noti8xy4
i8xy4:	; VX := VX + VY; carry in VF
	call.3	alusetup
	add.a	a,c
	move.2	c,@d0
	jump.3	savecarry
noti8xy4:

	move.p1	#5,c
	brne.p	c,a,noti8xy5
i8xy5:	; VX := VX - VY; carry in VF
	call.3	alusetup
subcommon:
	not.b	a	; do monkey business to get inverted carry
	add.a	a,c
	inc.a	c
	move.2	c,@d0
	jump.3	savecarry
noti8xy5:

	move.p1	#6,c
	brne.p	c,a,noti8xy6
i8xy6:	; VX := VX >> 1; carry in VF
	call.3	alusetup
	move.b	c,a	
	srb.b	c
	move.2	c,@d0	; store result
	move.b	a,c	; use low bit of original byte for carry
	jump.3	lsbcarry
noti8xy6:
	move.p1	#7,c
	brne.p	c,a,noti8xy7
i8xy7:	; VX := VY - VX; carry in VF
	call.3	alusetup
	swap.a	a,c
	jump.3	subcommon

noti8xy7:
	move.p1	#e,c
	brne.p	c,a,noti8xye
i8xye:	; VX := VX << 1; carry in VF
	call.3	alusetup
	add.a	c,c
	move.2	c,@d0
	jump.3	savecarry
noti8xye:
	retsetc


ia:	; ANNN, set I
	call.3	nnnc
	move.a	c,r0	; assign to I
	retclrc

ib:	; parametric jump to NNN+V0
	call.3	varpd0
	call.3	nnnc
	clr.a	a
	move.b	@d0,a
	add.a	a,c
	move.a	c,r3	; assign to pc
	retclrc


ic:	; pseudo-random number

	call.3	varpd0		; now d0 points to VX
	move.p5	crcval,c
	swap.a	c,d0		; point d0 to hardware crc
	move.2	@d0,a		; read the low byte of the crc
	swap.a	c,d0		; now d0 points to VX again
	add.a	2,d1		; point to second byte of instruction
	move.b	@d1,c		; get mask
	sub.a	2,d1		; restore d1
	and.b	a,c		; mask
	move.b	c,@d0		; store result
	retclrc


id_abort:
	jump.3	fx0a_abort


id:	; DXYN, show N-byte sprite at MI at screen coordinates (X,Y)
	;       I doesn't change

	; synchronize with 64 Hz tick
tickwait:
	call.3	realtime
	brcs	id_abort	; a realtime key was pressed
	brz.p	c,tickwait	; wait until a tick occus

	call.3	save_rregs	; save r0..r3

	move.a	r0,c		; get I
	call.3	virtophy
	move.a	c,r0		; now r0 points to sprite

	call.3	varxcvarya
	move.a	c,d		; save X in d
	move.p2	#1f,c
	and.b	c,a		; mask Y to range 0..31, leave in a
	move.p2	#3f,c
	and.b	c,d		; mask X to range 0..63, save in d

	; get the number of bytes in the sprite (preserving a and d)
	add.a	2,d1		; point to N field

	clr.b	c
	move.1	@d1,c
	add.b	a,c		; now c contains Y + sprite length
	move.b	c,b
	move.p2	#20,c
	sub.b	c,b		; now b contains no. of overshoot lines
	brcc	oshoot
	clr.b	b		; no overshoot
oshoot:
	clr.b	c		; get sprite length again
	move.1	@d1,c
	sub.b	b,c		; subtract overshoot
	move.1	c,0,p		; now p contains adjusted length
	move.1	p,c,15		; byte counter in nibble 15 of c
	move.1	14,p
	clr.p	c		; collision flag in nibble 14 of c
	move.1	0,p
	sub.a	2,d1		; back to beginning of instruction

	call.3	sprite		; do it

	call.3	restore_rregs

	call.4	varfpd0		; d0 points to VF
	clr.b	c
	move.1	14,p
	brz.p	c,nocolls
	inc.b	c
nocolls:
	move.b	c,@d0		; store collision flag
	move.1	0,p

	retclrc	; id


ie:	; skip on key pressed / not pressed
	call.3	varpd0
	clr.a	c
	move.b	@d0,c	; Telmac key number
	call.3	testkey
	clr.b	d
	move.p	c,d	; now d.b is nonzero iff key was pressed
	
	add.a	2,d1	; point to second byte of instruction
	move.b	@d1,a
	sub.a	2,d1
	move.p2	#9e,c
	breq.b	c,a,doex9e
	move.p2	#a1,c
	breq.b	c,a,doexa1
	retsetc

doex9e:	move.b	d,c
	clr.b	a
	jump.3	skipne	; skip iff d!=0 (key was pressed)

doexa1:	move.b	d,c
	clr.b	a
	jump.3	skipeq	; skip iff d==0 (key was not pressed)


; kwait -- wait for key, return it in low byte of c
; In: none
; Out: key code in low byte of c
; Uses: most everything except d0
;
; The beep-and-wait-until-released behaviour may seem a bit crummy,
; but we're just trying to emulate the original Telmac PROM monitor
; keyboard input routine as closely as possible.
kwait:
	swap.a	c,d0
	push.a	c		; save d0 value

	clr.a	d		; low nibble of d used for key code
kwalo:	move.a	d,c
	call.3	testkey
	brnz.p	c,pressed
	call.3	realtime	; preserves d
	brcs	kwabort
	inc.p	d		; loop through keys 0..15
	jump.3	kwalo

pressed:
	call.3	soundpd0
	move.p2	#04,c
	move.2	c,@d0		; set sound timer to #04
	call.3	realtime	; make some noise
	brcs	kwabort
	move.a	d,c
	call.3	testkey
	brnz.p	c,pressed	; wait until key is released

	pop.a	c		; restore d0 value
	move.a	c,d0
	move.b	d,c
	retclrc

kwabort:
	pop.a	c		; adjust stack
	retsetc

if:	; misc. functions using VX
	; d0 is set up to point to VX

	call.3	varpd0
	add.a	2,d1	; point to second byte of instruction
	move.b	@d1,a
	sub.a	2,d1

	move.p2	#07,c
	brne.b	c,a,notifx07
ifx07:	; read timer
	swap.a	c,d0
	push.a	c
	call.3	timerpd0
	move.b	@d0,a
	pop.a	c
	swap.a	c,d0
	move.b	a,@d0
	retclrc
notifx07:

	move.p2	#0a,c
	brne.b	c,a,notifx0a
ifx0a:	call.3	kwait
	brcs	fx0a_abort
	move.b	c,@d0
	retclrc
fx0a_abort:
	pop.a	c	; adjust stack for forced return
	jump.3	rtcarry

notifx0a:

 	move.p2	#15,c
	brne.b	c,a,notifx15
ifx15:	; set timer
	move.b	@d0,c
	push.a	c
	call.3	timerpd0
	pop.a	c
	move.b	c,@d0
	retclrc
notifx15:

 	move.p2	#18,c
	brne.b	c,a,notifx18
ifx18:	; set sound
	move.b	@d0,c
	push.a	c
	call.3	soundpd0
	pop.a	c
	move.b	c,@d0
	retclrc
notifx18:

 	move.p2	#1e,c
	brne.b	c,a,notifx1e
ifx1e:	; increment I by VX
	clr.a	c
	move.b	@d0,c
	move.a	r0,a	; get old I
	add.x	c,a	; increment, modifying only 3 low nibbles
	retcs		; it wrapped around #1000
	move.a	a,r0	; save new I
	retclrc
notifx1e:

 	move.p2	#29,c
	brne.b	c,a,notifx29
ifx29:	; point to hex display pattern
	; assumes that the hex patterns are at virtual 0000
	clr.a	c
	move.1	@d0,c	; use low nibble of variable
	move.a	c,a	
	add.a	c,c	; * 2
	add.a	c,c	; * 4
	add.a	a,c	; * 5
	move.a	c,r0	; this is the new I
	retclrc
notifx29:

 	move.p2	#33,c
	breq.b	c,a,ifx33
	jump.3	notifx33
ifx33:	; 8-bit binary to decimal conversion
	move.b	@d0,c
	move.b	c,d		; d contains the byte to convert

	move.a	pc,a
ref12:	move.p5	dectab-ref12,c
	add.a	a,c
	move.a	c,d0		; d0 points to the conversion table

	clr.a	a		; a accumulates decimal result	
cnvbit:	brz.b	d,cnvend
	move.b	d,c
	brbc	0,c,skpbit	; jump if low-order bit is zero
	move.3	@d0,c
	setdec
	add.a	c,a		; only 3 low nibbles contain real data
	sethex
skpbit:	add.a	3,d0
	srb.b	d
	jump.3	cnvbit

cnvabort:
	retsetc

cnvend:
	move.a	a,b		; save the decimal value
	move.a	r0,c		; get I
	move.p5	#00ffd,a	; is I > 0FFD hex?
	retgt.a	c,a		; protect memory above 0FFF
	call.3	virtophy
	move.a	c,d0		; virtual I in d0
	move.a	b,a		; restore the decimal value

	clr.a	c
	move.1	2,p
	move.p	a,@d0		; most significant digit first
	add.a	1,d0
	move.p	c,@d0		; zero
	add.a	1,d0
	move.1	1,p
	move.p	a,@d0		; middle digit
	add.a	1,d0
	move.p	c,@d0		; zero
	add.a	1,d0
	move.1	0,p
	move.p	a,@d0		; least significant digit
	add.a	1,d0
	move.p	c,@d0		; zero
	; I doesn't change
	retclrc
notifx33:

 	move.p2	#55,c
	brne.b	c,a,notifx55
ifx55:	; save vars in memory
	call.3	varcopysetup
savelo:
	move.b	@d0,c		; read a byte from variable
	move.b	c,@d1		; store in MI
	swap.a	c,d0		; get d0 to c
	move.a	c,d0
	brge.a	c,a,doret1	; are we ready yet?
	add.a	2,d1
	add.a	2,d0
	move.a	r0,c		; get I value
	inc.x	c		; increment 3 low nibbles
	retcs			; if carry, we might overwrite #1000
	move.a	c,r0		; I changes permanently
	jump.3	savelo
doret1:
	retclrc

notifx55:

 	move.p2	#65,c
	brne.b	c,a,notifx65
ifx65:	; restore vars from memory
	call.3	varcopysetup
restolo:
	move.b	@d1,c		; read a byte at MI
	move.b	c,@d0		; store in variable
	swap.a	c,d0		; get d0 to c
	move.a	c,d0
	brge.a	c,a,doret1	; are we ready yet?
	add.a	2,d1
	add.a	2,d0
	move.a	r0,c		; get I value
	inc.x	c		; increment 3 low nibbles
	retcs			; if carry, we wrapped around #1000
	move.a	c,r0		; I changes permanently
	jump.3	restolo
notifx65:
	; unknown FxNN instruction
	retsetc


; save registers r0..r3
save_rregs:
	move.a	r4,a		; get start of data area
	move.p5	ofs_regsave,c
	add.a	a,c
	move.a	c,d0

	move.a	r0,c
	move.a	c,@d0
	add.a	5,d0
	move.a	r1,c
	move.a	c,@d0
	add.a	5,d0
	move.a	r2,c
	move.a	c,@d0
	add.a	5,d0
	move.a	r3,c
	move.a	c,@d0
	add.a	5,d0
	ret


; restore registers r0..r3
restore_rregs:
	move.a	r4,a		; get start of data area
	move.p5	ofs_regsave,c
	add.a	a,c
	move.a	c,d0

	move.a	@d0,c
	move.a	c,r0
	add.a	5,d0
	move.a	@d0,c
	move.a	c,r1
	add.a	5,d0
	move.a	@d0,c
	move.a	c,r2
	add.a	5,d0
	move.a	@d0,c
	move.a	c,r3
	add.a	5,d0
	ret


; sprite: draw a CHIP-8 "sprite", 8 pixels wide by 1..15 pixels high
;
; in: r0.a  points to sprite data
;     a.a   contains x coordinate
;     d.a   contains y coordinate
;     c.14  zero initial value for collision flag
;     c.15  number of lines in sprite
; out: c.14 collision flag
;
; register usage:
; a,c used for scratch
;  c.15 contains sprite byte (line) count
;  c.14 contains collision flag
;  c.13 is used as temporary save location for p
;  c.12 is nonzero in "short mode" (2x1 pixels)
; b contains the byte to display
; d contains the 32-bit pixel string
; r0 points to sprite data
; r1 points to linetab
; r2 contains the X offset in nibbles from the beginning of the lcd line
; r3 contains entry point to pixel alignment shifts

sprite:
	move.1	12,p
	move.p1	0,c		; set "short flag"
	move.1	0,p

	move.1	12,p
	brnz.p	c,short1	; "short mode"?
	add.a	a,a		; 2Y (the chip-8 pixels are 2 lines high)
short1:	move.1	0,p		; (but not in "short mode"

	move.a	a,c		; multiply by 5 to get index into linetab
	add.a	a,a
	add.a	a,a
	add.a	a,c		; now c contains index to linetab

	move.a	r4,a		; get start of data area
	add.a	c,a
	move.p5	ofs_linetab,c
	add.a	a,c

	move.a	c,r1		; r1 is the linetab pointer

	; calculate X offset in nibbles from the beginning of the lcd line
	move.a	d,c		; c = X
	srb.a	c		; convert pixels to pixel octets
	srb.a	c
	srb.a	c
	add.a	c,c		; convert pixel octets to nibbles
	add.a	c,c
	move.a	c,r2		; r2 contains offset from beginning of line

	; calculate entry point to alignment shifts
	move.p2	#07,c		; d should still contain X
	and.b	c,d		; mask out 3 low bits
	add.a	d,d		; the shift instructions are 2 nibbles each
	move.a	pc,a		
ref11:	move.p5	shifts-ref11,c
	add.a	a,c
	add.a	d,c
	move.a	c,r3		; r3 now contains entry point to shifts

linelo:
	move.a	r0,c		; get sprite pointer
	move.a	c,d0
	move.2	@d0,c		; byte to display
	clr.a	b
	move.b	c,b		; ..to low byte of b; next byte is clear
	swap.a	c,d0
	add.a	2,c		; advance to next sprite byte
	move.a	c,r0		; save sprite pointer

	; the low byte of b now contains the sprite byte

	move.a	r3,c		; get shift entry point
	jump.a	c		; jump to the appropriate shift instruction


shifts:	add.a	b,b		; two-nibble instructions
	add.a	b,b
	add.a	b,b
	add.a	b,b
	add.a	b,b
	add.a	b,b
	add.a	b,b
	add.a	b,b

	move.a	pc,a
ref2:	move.p5	pixtab-ref2,c
	add.a	c,a		; beginning of pixtab is in a

	; keep &pixtab[0] in a at all times
	clr.a	c
	move.p	b,c		; extract a nibble from b
	add.a	c,c		; times two
	add.a	a,c		; add beginning of pixtab
	move.a	c,d0		; point d0 to pixtab byte
	move.b	@d0,c
	move.b	c,d		; now 8 more pixels in d

	sln.w	d
	sln.w	d
	srn.a	b

	clr.a	c
	move.p	b,c		; extract a nibble from b
	add.a	c,c		; times two
	add.a	a,c
	move.a	c,d0		; point d0 to pixtab byte
	move.b	@d0,c
	move.b	c,d		; now 8 more pixels in d

	sln.w	d
	sln.w	d
	srn.a	b

	clr.a	c
	move.p	b,c		; extract a nibble from b
	add.a	c,c		; times two
	add.a	a,c
	move.a	c,d0		; point d0 to pixtab byte
	move.b	@d0,c
	move.b	c,d		; now 8 more pixels in d

	sln.w	d
	sln.w	d
	srn.a	b

	clr.a	c
	move.p	b,c		; extract a nibble from b
	add.a	c,c		; times two
	add.a	a,c
	move.a	c,d0		; point d0 to pixtab byte
	move.b	@d0,c
	move.b	c,d		; now 8 more pixels in d

	; now d contains 32 pixels

	move.a	r1,a		; get linetab pointer
	move.a	a,d0		; ..to d0
	move.a	@d0,c		; address of current line to c

	move.1	12,p
	brnz.p	c,short2
	add.a	5,a		; point 1 line ahead if "short mode",
short2:	add.a	5,a		; point 2 lines ahead otherwise
	move.1	0,p

	move.a	a,r1		; this is the new linetab pointer

	move.a	r2,a		; X offset in nibbles
	add.a	a,c		; add beginning of lcd line
	move.a	c,d0		; now d0 points to display buffer

	; now we operate on the display buffer with a word length
	; that is normally 32 bits, but near the right end we
	; must decrease it to avoid wrapping around and messing up
	; the left part of the display.  Therefore the word length
	; should be min(8, 32-xoff) nibbles.

	move.p2	32,c
	sub.b	a,c		; now c = 32-xoff
	move.p2	8,a
	brlt.b	c,a,clip	; if (32-xoff) is < 8, use that, else 8
	move.b	a,c
clip:	dec.b	c		; .wp field is (p+1) nibbles; compensate
	move.1	c,0,p		; set field size

	move.wp	@d0,c		; get old display buffer contents
	move.wp	c,a		; make a copy in a
	and.wp	d,c		; now c = (old and new), a = old, d = new
	brz.wp	c,nocoll

	; there has been a collision; set nibble 14 in c
	swap.1	p,c,13		; save p in nibble 13 of c
	move.1	14,p
	move.p1	1,c		; set collision flag in nibble 13 of c
	swap.1	p,c,13		; restore p
nocoll:
	swap.wp	d,c		; now d = (old and new), a = old, c = new
	or.wp	a,c		; now c = (old or new)
	not.wp	d
	and.wp	d,c		; now c = (old or new) and not(old and new)

	swap.1	p,c,13
	move.1	12,p
	brnz.p	c,short3
	swap.1	p,c,13

	move.wp	c,@d0		; store once
	add.a	16,d0		; advance by 34 to next scan line
	add.a	16,d0
	add.a	2,d0
	move.wp	c,@d0		; store again
	jump.3	noshort3
short3:
	swap.1	p,c,13
	move.wp	c,@d0		; store just once
noshort3:
	move.1	0,p
	
	dec.s	c
	brz.s	c,lineexit
	jump.3	linelo
lineexit:

	ret  ; sprite


; this lookup table serves a dual purpose: it swaps the bits in a nibble
; to convert from big-endian to little-endian format, and doubles each bit
; to lower the resolution to 64 pixels horizontally.
pixtab:
	data.b	!00000000
	data.b	!11000000
	data.b	!00110000
	data.b	!11110000
	data.b	!00001100
	data.b	!11001100
	data.b	!00111100
	data.b	!11111100
	data.b	!00000011
	data.b	!11000011
	data.b	!00110011
	data.b	!11110011
	data.b	!00001111
	data.b	!11001111
	data.b	!00111111
	data.b	!11111111


; 4x5 pixel hexadecimal character font patterns
hexfont:
	data.5 #F999F
	data.5 #72262
	data.5 #F8F1F
	data.5 #F1F1F
	data.5 #11F99
	data.5 #F1F8F
	data.5 #F9F8F
	data.5 #4421F
	data.5 #F9F9F
	data.5 #F1F9F
	data.5 #99F9F
	data.5 #E9E9E
	data.5 #F888F
	data.5 #E999E
	data.5 #F8F8F
	data.5 #88F8F
hexfontend:

; powers of two in BCD, for binary-to-decimal conversion
dectab:	data.3 #001
	data.3 #002
	data.3 #004
	data.3 #008
	data.3 #016
	data.3 #032
	data.3 #064
	data.3 #128

; table mapping Telmac hex key locations to HP48SX key codes
; lsn is bit mask to output, lsn is bit mask to mask input with
keytab:
	data.2	#41
	data.2	#88
	data.2	#48
	data.2	#28
	data.2	#84
	data.2	#44
	data.2	#24
	data.2	#82
	data.2	#42
	data.2	#22
	data.2	#81
	data.2	#21
	data.2	#18
	data.2	#14
	data.2	#12
	data.2	#11

; jump table for CHIP-8 instruction dispatching based on the first nibble

jumptab:
	data.4	i0-jtref
	data.4	i1-jtref
	data.4	i2-jtref
	data.4	i3-jtref
	data.4	i4-jtref
	data.4	i5-jtref
	data.4	i6-jtref
	data.4	i7-jtref
	data.4	i8-jtref
	data.4	i9-jtref
	data.4	ia-jtref
	data.4	ib-jtref
	data.4	ic-jtref
	data.4	id-jtref
	data.4	ie-jtref
	data.4	if-jtref

regsave:
	even	; pad to even number of nibbles

end:	; don't add stuff after this line.
================================ Cut here ================================
-- 
Andreas Gustafsson
Internet: gson@niksula.hut.fi
Voice: +358 0 563 5592


