103 lines
2.3 KiB
Markdown
103 lines
2.3 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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### Read
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- `,literal`, push label value to stack, prefixed with `LIT LEN`.
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- `.pointer`, push label value to stack.
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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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### 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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### 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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```
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:dev/w fff9 ( const write port )
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;i 1 ( var iterator )
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|0100 @RESET
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#00 ,dev/w STR ( set dev/write to console )
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@word1 "hello_world ( len: 0x0b )
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@loop
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IOW ( write to device#0 )
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,i LDR #01 ADD ,i STR ( increment itr )
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,i LDR ( a = i )
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,word1 ,strlen JSR ( b = string length )
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NEQ ,loop ROT JSR? POP^ ( a != b ? loop )
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BRK
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@strlen #0001 ADD2 LDR RTS
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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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## TODOs
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- Line routine
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- On-screen debugger.
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- Auto-advance ldr?
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- Getting rid of IOR/IOW would be nice..
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- Sending from the wst to the rst, balance mode/flag?
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- Device that works like an extra memory bank
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- Draw a chr sprite.
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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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