Uxn

A stack-based VM, written in ANSI C.

Setup

If you wish to build your own emulator, you can create a new instance of Uxn like:

#include "uxn.h"

Uxn u;

if(!bootuxn(&u))
	return error("Boot", "Failed");
if(!loaduxn(&u, argv[1]))
	return error("Load", "Failed");
if(!init())
	return error("Init", "Failed");

evaluxn(u, u->vreset); /* Once on start */
evaluxn(u, u->vframe); /* Each frame

Assembly Syntax

• ADD, an opcode.
• @label, assign the current address to a label.
• ;variable 2, assign an address to a label automatically.
• :const 1a2b, assign an address to a label manually.
• &macro { x 2 y 2 }, define a macro named macro.
• #1a, a literal byte/short.
• +1a, a literal signed byte/short.
• -1a, a literal signed byte/short(negative).
• .ab, a raw byte/short in memory.
• ,literal, push label address to stack, prefixed with LIT LEN.
• =label, helper to STR, equivalent to ,label STR, or label STR2.
• ~label, helper to LDR, equivalent to ,label LDR2, or ,label LDR2.
• |0010, move to position in the program.
• <23, move the program position 23 bytes backward.
• >12, move the program position 12 bytes forward.
• ( comment ), toggle parsing on/off.
• [ 0123 abcd ], write shorts to memory.
• [ Hello World ], write text to memory.

Operator modes

• #1234 #0001 ADD2, 16-bits operators have the short flag 2.
• #12 #11 GTH JMP?, conditional operators have the cond flag ?.
• +21 -03 MULS, signed operators have the cond flag S.
• ADDS2?, modes can be combined.

( hello world )

:dev/w fff9 ( const write port )

|0100 @RESET 
	
	#00 =dev/w ( set dev/write to console ) 
	,text1 ,print-label JSR ( print to console )

BRK

@print-label ( text )

	@cliloop
		DUP2 LDR IOW                             ( write pointer value to console )
		#0001 ADD2                               ( increment string pointer )
		DUP2 LDR #00 NEQ ,cliloop ROT JMP? POP2  ( while *ptr!=0 goto loop )
	POP2
		
RTS                 

@text1 [ Hello World ] <1 .00 ( add text to memory, return 1 byte, add null byte )

|c000 @FRAME
|d000 @ERROR 

|FFF0 [ f3f0 f30b f30a ] ( palette )
|FFFA .RESET .FRAME .ERROR

Emulator

Controller(dev/ctrl)

A device that works like a NES controller, each button is a bit from a single byte. Press h to toggle debugger.

• 0x01 Ctrl
• 0x02 Alt
• 0x04 Escape
• 0x08 Return
• 0x10 Up
• 0x20 Down
• 0x40 Left
• 0x80 Right

TODOs

• Line routine
• Getting rid of IOR/IOW would be nice..
• Example of button pointing to a subroutine

Misc TODOs

• Includes
• Defines
• Print unused labels

Refs

https://code.9front.org/hg/plan9front/file/a7f9946e238f/sys/src/games/nes/cpu.c http://www.w3group.de/stable_glossar.html http://www.emulator101.com/6502-addressing-modes.html http://forth.works/8f0c04f616b6c34496eb2141785b4454 https://justinmeiners.github.io/lc3-vm/