Tobias V. Langhoff tobiasvl

CHIP-8 extensions and compatibility

This document is intended as a well-sourced and exhaustive documentation of all extensions to CHIP-8. They all use the standard CHIP-8 interpreter as a base, mentioning what additions and changes they make to that common base.

This list is mostly for historical purposes; few of the extensions listed here had a considerable number of programs written for them. It could serve as a reference for CHIP-8 emulator/interpreter developers who want to support the various incompatible instructions and behaviors that have cropped up in different interpreters over the decades. Perhaps the instructions listed here can also inspire someone to make their own modern CHIP-8 extension (of which there have been a couple, see the bottom of the list).

A note on modern implementations

The only CHIP-8 extensions in active use today (beyond basic CHIP-8) are Super-CHIP 1.1 and the relative newcomer XO-CHIP.

	# Copied from https://github.com/aseprite/aseprite/blob/master/INSTALL.md#skia-on-linux

	sudo yum install -y gcc-c++ cmake ninja-build libX11-devel libXcursor-devel mesa-libGL-devel fontconfig-devel

	mkdir $HOME/deps
	cd $HOME/deps
	git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
	git clone -b aseprite-m71 https://github.com/aseprite/skia.git
	export PATH="${PWD}/depot_tools:${PATH}"
	cd skia

	poke(24364,3)w={10,11,8,2,12}o="★●♥◆✽"b={[0]=0,0,0,0,0,0}z=56h=6::_::add(b,ceil(rnd(5)))cls()j=6*(8-flr(z/8))-6
	?"██",8(h%6),z+8flr(h/6),5
	?t(),49,58
	for q=0,j+6 do
	u=abs(b[q])for i in all{1,6}do
	if(q<j and(i>1or q%6>1)and u==abs(b[q-i])and u==abs(b[q-i2])and u!=0)b[q-i]=-u b[q-i2]=-u b[q]=-u
	end
	?sub(o,u,u),(q%6)8,z+flr(q/6)8,q<j and w[u]or 1
	end
	for q=0,j do

	[
	{
	"backcolor": "#C2C3C7",
	"name": "PICO-8 devkit keyboard",
	"author": "tobiasvl",
	"switchMount": "cherry",
	"switchBrand": "cherry",
	"switchType": "MX1A-G1xx"
	},
	[

	-- four directions, 16 tokens
	for i=0,1,0.25 do
	local x,y=cos(i),sin(i)
	end

	-- eight directions, 24 tokens
	for i=0.125,1,0.125 do
	local x,y=flr(cos(i)+.5),flr(sin(i)+.5)
	end

	z="lights out"poke(24364,3)::x::flip()cls()k=btnp()w={[0]="","▒","█"}f=flr
	?z,12,18,stat(95)%4
	?"z: classic\nx: 2000",12,32,7
	if(k<9)goto x
	if(k>16)w[3]="█"
	b={}p=2m=0
	for i=1,35 do
	b[i]=i%7<2 and 0or 2
	end::_::flip()cls()
	?m,30,54

	u=64
	x,y=u,u
	es={}c=circfill
	f=abs
	p=cos
	o=sin::_::
	if(btn(0))x-=1
	if(btn(1))x+=1
	if(btn(2))y-=1
	if(btn(3))y+=1

	poke(24364,3)x="웃"v="▥"h="▤"b={}for i=1,36 do b[i]=i%9<2 and""or"█"end for i in all{"⬆️","➡️",h,"⬅️","⬇️",v,x}do repeat f=1+flr(rnd(36))until b[f]!=""b[f]=i
	if(i==x)p=f
	end::_::t=btnp cls()for i=0,35 do
	k=b[i+1]
	?k,i%98,6flr(i/9)+20,k==x and 11 or 7
	end b[p]=""q=p
	if(t(0))q-=1
	if(t(1))q+=1
	if(t(2))q-=9
	if(t(3))q+=9

	get_map_position:
	; from a sprite's pixel position, get the BG map address.
	; d: Y pixel position
	; e: X pixel position
	; hl: returned map address
	ld h, HIGH(_SCRN0) >> 2

	; Y
	ld a, [rSCY] ; account for scroll
	sub a, 16 ; account for base sprite offset

	: keys
	0
	1
	2
	3
	4
	5
	6
	7
	8