106 lines
2.6 KiB
Markdown
106 lines
2.6 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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- `ADD`, an opcode.
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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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- `#1a`, a literal byte/short.
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- `+1a`, a literal signed byte/short.
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- `-1a`, a literal signed byte/short(negative).
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- `.ab`, a raw byte/short in memory.
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- `,literal`, push label address to stack, prefixed with `LIT LEN`.
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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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- `|0010`, move to position in the program.
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- `( comment )`, toggle parsing on/off.
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- `[ 0123 abcd ]`, write shorts to memory.
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- `[ Hello World ]`, write text to memory.
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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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( hello world )
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&Console { pad 8 char 1 byte 1 short 2 }
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|0100 @RESET
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,text1 ,print-label JSR
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,text2 ,print-label JSR
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#ab =dev/console.byte
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#cdef =dev/console.short
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BRK
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@print-label ( text )
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@print-label-loop
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DUP2 LDR =dev/console.char ( write pointer value to console )
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#0001 ADD2 ( increment string pointer )
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DUP2 LDR #00 NEQ ,print-label-loop ROT JMP? POP2 ( while *ptr!=0 goto loop )
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POP2
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RTS
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@text1 [ Hello World 0a00 ] ( store text with a linebreak and null byte )
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@text2 [ Welcome to UxnVM 0a00 ]
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|c000 @FRAME
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|d000 @ERROR
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|FF00 ;dev/console Console
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|FFF0 .RESET .FRAME .ERROR ( vectors )
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|FFF8 [ 13fd 1ef3 1bf2 ] ( palette )
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```
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## TODOs
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### OS Boot Disk
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- Load external disk in disk2
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- Build hex editor
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### Assembler
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- Includes
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- Defines
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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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