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

Assign

• @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.

Write

• ADD, an opcode.
• #1a, a literal byte.
• #12ef, a literal short.
• +1a, a literal signed byte.
• +12ef, a literal signed short.
• -1a, a literal signed byte(negative).
• -12ef, a literal signed short(negative).
• .ab, a raw byte in memory.
• .abcd, a raw short in memory.
• ,literal, push label address to stack, prefixed with LIT LEN.

Special

• ( comment ), toggle parsing on/off.
• |0010, move to position in the program.
• "hello, push literal bytes for word "hello".
• =label, helper to STR, equivalent to ,label STR, or label STR2.
• ~label, helper to LDR, equivalent to ,label LDR2, or ,label LDR2.

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.

( comment )

:dev/w fff9 ( const write port )

|0100 @RESET 

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

BRK

@string " Hello World "                      ( add string to memory )

|c000 @FRAME BRK
|d000 @ERROR BRK 

|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

• LDR/STR helpers
• Line routine
• On-screen debugger.
• Getting rid of IOR/IOW would be nice..
• Sending from the wst to the rst, balance counter?

Misc TODOs

• Includes
• Defines
• Lint, 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/