Uxn

A stack-based VM, written in ANSI C.

Assembly Syntax

Write

• ;variable, automatically assign an address to a label.
• :const FFCF, manually assign an address to a label.
• @label, assign the current address to a label.

Read

• ,literal, push label value to stack, prefixed with LIT LEN.
• .pointer, push label value to stack.

Special

• ( comment ), toggle parsing on/off.
• |0010, move to position in the program.
• "hello, push literal bytes for word "hello".
• #04, a zero-page address, equivalent to ,0004.

Operator modes

• ,1234 ,0001 ADD^, 16-bits operators have the short flag ^.
• ,12 ,11 GTH JMP?, conditional operators have the cond flag ?.

( hello world )

;iterator

|0100 @RESET

@word1 "hello_world ( len: 0x0b )

@loop
	,00 IOW ( write to device#0 )
	,incr JSR ( increment itr )
	,word1 ,strlen JSR ( get strlen )
	NEQ ,loop ROT JSR? ( loop != strlen )

BRK

@strlen
	,0001 ADD^ LDR
	RTS

@incr
	,iterator LDR
	,01 ADD
	,iterator STR 
	,iterator LDR
	RTS

|c000 @FRAME BRK 
|d000 @ERROR BRK 
|FFFA .RESET .FRAME .ERROR

TODOs

• Implement signed flag to operators.
• On-screen debugger.
• 16b mode for str/ldr
• Auto-advance ldr?
• Getting rid of IOR/IOW would be nice..

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/