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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

Define

@label, assign the current address to a label.
$label, assign the current address to a local 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.

Program

ADD, push an opcode.
.address, push label address to memory.
,literal, push label address to stack, prefixed with LIT LEN.
#1a, push a literal byte/short.
+1a, push a literal signed byte/short.
-1a, push a literal signed byte/short(negative).
|0010, move to position in the program.

Helpers

=label, helper to STR, equivalent to ,label STR, or label STR2.
~label, helper to LDR, equivalent to ,label LDR2, or ,label LDR2.

Blocks

( 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 )

&Console { pad 8 char 1 byte 1 short 2 }

|0100 @RESET 
	
	,text1 ,print-label JSR2
	,text2 ,print-label JSR2
	#ab =CNSL.byte
	#cdef =CNSL.short

BRK

@print-label ( text )
	
	$loop NOP
		( send ) DUP2 LDR =CNSL.char
		( incr ) #0001 ADD2
		( loop ) DUP2 LDR #00 NEQ ^$loop MUL JMPS 
	POP2

RTS    

@text1 [ Welcome 20 to 20 UxnVM 0a00 ]
@text2 [ Hello 20 World 0a00 ] 

|c000 @FRAME
|d000 @ERROR 

|FF00 ;CNSL Console

|FFF0 .RESET .FRAME .ERROR ( vectors )
|FFF8 [ 13fd 1ef3 1bf2 ] ( palette )

TODOs

OS Boot Disk

Load external disk in disk2
Build hex editor

Assembler

Includes
Defines
Local loops
Jump helpers

Notes

Conditional Jumping

I've considered automatically popping an amount of items from the stack equal to the offset between the opcode's push/pop to make the stack length more predictable, and making the pattern JMP? POP2 unecessary, but that idea would make DUP? unusable. That change was reverted.

Palettes

[ 6a03 4a0d aa0c ], purple/cyan
[ a1f3 a14d a16c ], grey-pink/teal

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/

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Uxn