mirror of https://git.sr.ht/~rabbits/uxn
94 lines
1.8 KiB
Markdown
94 lines
1.8 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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## Assembly Syntax
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### Write
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- `;variable`, automatically assign an address to a label.
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- `:const FFCF`, manually assign an address to a label.
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- `@label`, assign the current address to a label.
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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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### 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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- `#04`, a zero-page address, equivalent to `,0004`.
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### Operator modes
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- `,1234 ,0001 ADD^`, 16-bits operators have the short flag `^`.
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- `,12 ,11 GTH JMP?`, conditional operators have the cond flag `?`.
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```
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( hello world )
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;iterator
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:dev1r FFF0
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:dev1w FFF1
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|0100 @RESET
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@word1 "hello_word ( len: 0x0b )
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@loop
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,dev1w STR ( write to stdout )
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,incr JSR ( increment itr )
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,word1 ,strlen JSR ( get strlen )
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NEQ ,loop ROT JSR? ( loop != strlen )
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BRK
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@strlen
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,0001 ADD^ LDR
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RTS
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@incr
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,iterator LDR
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,01 ADD
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,iterator STR
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,iterator LDR
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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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### Assembler
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- Implement shorthand operators
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- Signed operations
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### CPU
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- Signed operations
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- Catch overflow/underflow
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- A Three-Way Decision Routine(http://www.6502.org/tutorials/compare_instructions.html)
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- Draw pixel to screen
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- Redo overflow/underflow mappping
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- Detect mouse click
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- SDL Layer Emulator
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- Build PPU
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### Devices
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- Devices each have an input byte, an output byte and two request bytes.
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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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