mirror of https://git.sr.ht/~rabbits/uxn
120 lines
2.8 KiB
Markdown
120 lines
2.8 KiB
Markdown
# Uxn
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A [stack-based VM](https://wiki.xxiivv.com/site/uxn.html), written in ANSI C.
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## Setup
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If you wish to build your own emulator, you can create a new instance of Uxn like:
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```
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#include "uxn.h"
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Uxn u;
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if(!bootuxn(&u))
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return error("Boot", "Failed");
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if(!loaduxn(&u, argv[1]))
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return error("Load", "Failed");
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if(!init())
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return error("Init", "Failed");
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evaluxn(u, u->vreset); /* Once on start */
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evaluxn(u, u->vframe); /* Each frame
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```
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## Assembly Syntax
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### Assign
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- `@label`, assign the current address to a label.
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- `;variable 2`, assign an address to a label automatically.
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- `:const 1a2b`, assign an address to a label manually.
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- `¯o { x 2 y 2 }`, define a macro named `macro`.
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### Write
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- `ADD`, an opcode.
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- `#1a`, a literal byte.
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- `#12ef`, a literal short.
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- `+1a`, a literal signed byte.
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- `+12ef`, a literal signed short.
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- `-1a`, a literal signed byte(negative).
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- `-12ef`, a literal signed short(negative).
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- `.ab`, a raw byte in memory.
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- `.abcd`, a raw short in memory.
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- `,literal`, push label address to stack, prefixed with `LIT LEN`.
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### Special
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- `( comment )`, toggle parsing on/off.
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- `|0010`, move to position in the program.
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- `"hello`, push literal bytes for word "hello".
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- `=label`, helper to STR, equivalent to `,label STR`, or `label STR2`.
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- `~label`, helper to LDR, equivalent to `,label LDR2`, or `,label LDR2`.
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### Operator modes
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- `#1234 #0001 ADD2`, 16-bits operators have the short flag `2`.
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- `#12 #11 GTH JMP?`, conditional operators have the cond flag `?`.
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- `+21 -03 MULS`, signed operators have the cond flag `S`.
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- `ADDS2?`, modes can be combined.
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```
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( comment )
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:dev/w fff9 ( const write port )
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|0100 @RESET
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,string ( add string pointer to stack )
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@loop
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DUP2 LDR IOW ( write pointer value to console )
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#0001 ADD2 ( increment string pointer )
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DUP2 LDR #00 NEQ ,loop ROT JMP? POP2 ( while *ptr!=0 goto loop )
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BRK
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@string " Hello World " ( add string to memory )
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|c000 @FRAME BRK
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|d000 @ERROR BRK
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|FFFA .RESET .FRAME .ERROR
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```
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## Emulator
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### Controller(dev/ctrl)
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A device that works like a NES controller, each button is a bit from a single byte. Press `h` to toggle debugger.
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- `0x01` Ctrl
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- `0x02` Alt
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- `0x04` Escape
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- `0x08` Return
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- `0x10` Up
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- `0x20` Down
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- `0x40` Left
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- `0x80` Right
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## TODOs
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- Line routine
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- Getting rid of IOR/IOW would be nice..
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- Example of button pointing to a subroutine
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- Labels should not have the trailing space
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### Misc TODOs
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- Includes
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- Defines
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- Print unused labels
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## Refs
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https://code.9front.org/hg/plan9front/file/a7f9946e238f/sys/src/games/nes/cpu.c
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http://www.w3group.de/stable_glossar.html
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http://www.emulator101.com/6502-addressing-modes.html
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http://forth.works/8f0c04f616b6c34496eb2141785b4454
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https://justinmeiners.github.io/lc3-vm/
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