# Uxn
A [stack-based VM](https://wiki.xxiivv.com/site/uxn.html), 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
### 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.
- Auto-advance ldr?
- Getting rid of IOR/IOW would be nice..
- Sending from the wst to the rst, balance mode/flag?
- Device that works like an extra memory bank
- Line routine
- LineRect routine
- Draw a chr sprite.
## 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/