Ancestors

Toot

Written by Ellie on 2025-01-10 at 02:34

We have an instruction decoder. Hopefully correctly. #mos6502 #nes_emulator

https://www.masswerk.at/6502/6502_instruction_set.html

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Descendants

Written by Ellie on 2025-01-11 at 04:07

All the addressing modes and operators implemented, a (unsynchronized) clock, a byte array 0x0000-0xffff bolted on as temporary ram, and a tiny bit of machine code jammed into the first dozen bytes by main.

This silly little computer can loop and increment the number at 0x0f forever!

[#]mos6502 #nes_emulator

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Written by Ellie on 2025-01-11 at 04:11

Next steps: need to implement a cartridge rom loader and mapper.

And use them to write tests that load blargg roms, then hunt down opcode implementation bugs.

[#]nes

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Written by Scott VE3QBZ on 2025-01-11 at 04:10

@ellie I wrote a Motorola 6800 emulator a long time ago, I hope you are having as much fun as I did!

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Written by Ellie on 2025-01-11 at 04:15

@ve3qbz transcribing the 256-entry instruction table from photocopied spec sheet into a giant lookup table of function pointers was tedious.

But heck the pay-off of watching that memory dump tick up is so rewarding.

[#]nes_emulator

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Written by Scott VE3QBZ on 2025-01-11 at 04:16

@ellie YES! The array of function pointers to launch opcodes was the most satisfying little bit of code I think I ever wrote, because it's so elegant.

:) You are having fun!

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