# Uxn A [stack-based VM](https://wiki.xxiivv.com/site/uxn.html), 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 :dev1r FFF0 :dev1w FFF1 |0100 @RESET @word1 "hello_word ( len: 0x0b ) @loop ,dev1w STR ( write to stdout ) ,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 ### Assembler - Implement shorthand operators - Signed operations ### CPU - Signed operations - Catch overflow/underflow - A Three-Way Decision Routine(http://www.6502.org/tutorials/compare_instructions.html) - Draw pixel to screen - Redo overflow/underflow mappping - Detect mouse click - SDL Layer Emulator - Build PPU ### Devices - Devices each have an input byte, an output byte and two request bytes. ## 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/