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136 lines
5.7 KiB
Markdown
136 lines
5.7 KiB
Markdown
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Moa
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===
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###### *Started September 26, 2021*
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Moa is an emulator/simulator for computers using various 68000 and Z80 CPUs and
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peripherals. The original idea was to emulate the computer I had built as part
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of the [Computie project](https://jabberwocky.ca/projects/computie/).
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Currently it can simulate the Sega Genesis, Computie (68000), and the TRS-80
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Model I (Z80). Support for the Macintosh 512k is partially implemented but the
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ROM still wont boot.
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For more details on how it works, check out this post about how I started the project:
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[Making a 68000 Emulator in Rust](https://jabberwocky.ca/posts/2021-11-making_an_emulator.html)
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For more about the Sega Genesis support, check out this series I wrote about implementing it:
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[Emulating the Sega Genesis](http://jabberwocky.ca/posts/2022-01-emulating_the_sega_genesis_part1.html)
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Sega Genesis/MegaDrive
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----------------------
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From the project root, run the following:
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```
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cargo run -p moa-minifb --release --bin moa-genesis -- <ROM FILE>
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```
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The Genesis emulator is slowly coming along. It can play a decent number of
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game, but some games wont display anything, and a few games run but don't
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respond to the controller input. Games that require extra memory or nvram that
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would normally be inside the cartridge usually crash.
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It only supports NTSC mode at the moment, and only VDP mode 5 (not the backwards
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compatible mode 4). I've rewritten the frame drawing code to operate pixel by
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pixel, so it will now draw all the layers, including the window, sort out the
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priority of the pixels, and almost accurately implement the shadow and highlight
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colour modes. Audio is not implemented yet.
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There are still some problems like the colour of Tails in the Sonic 2 title
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screen being off. I'm not sure why that happens, but it could be trying to
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update the colours during the drawing of the frame, and since the code is
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drawing the entire frame at once when the vertical blanking period is reached,
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the on-the-fly changes don't have an affect.
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The game play is mostly working but the time in the upper left corner doesn't
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seem to progress
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Earthworm Jim was working before I fixed the controller behaviour in Sonic 2,
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which seems to have broken it in Earthworm Jim (and Mortal Kombat 1).
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The following gif was only recorded at 15 frames a second instead of the full
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60, so it appears jerky and some animations seem to freeze in the gif, even
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though that doesn't happen during normal play
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Computie
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--------
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For Computie, it can do everything the 68k-SMT board can do, including run the
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monitor program and load the Computie OS kernel and boot it from the
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CompactFlash card. To run it:
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```
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cargo run -p moa-console --bin moa-computie
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```
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It will open two PTYs: one for the serial terminal, and one for the SLIP
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connection. Once open, it will try to launch both `pyserial-miniterm` as a
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separate process and connect to the Computie PTY. It will also launch
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`slattach` with the associated setup commands to create the SLIP device on the
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host, and set up host routing. The exact commands in
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`src/machines/computie.rs` might need to be adjusted to work on different
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hosts.
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TRS-80
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------
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For the TRS-80, it can run Level I or Level II Basic, but it doesn't yet
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support a cassette tape drive or floppy drive. I haven't tested it that
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thoroughly either, so any help with it would be welcome. I mostly made it to
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test the Z80 cpu implementation in a simpler computer before I used in the
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Genesis emulator. The frontend uses the
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[`minifb`](https://github.com/emoon/rust_minifb) rust crate to open a window
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and render the characters to screen, as well as accept input from the keyboard.
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```
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cargo run -p moa-minifb --release --bin moa-trs-80
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```
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By default it will start Level I Basic. To use the other rom, add the option
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`--rom binaries/trs80/level2.rom`
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The characters are being drawn pixel by pixel (6x8) using characters I drew
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using [this handy website](https://maxpromer.github.io/LCD-Character-Creator/).
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They aren't a perfect match of the characters used by the TRS-80
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General Options
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---------------
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By default, the minifb frontend will scale the window by 2. This can be
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changed with the `--scale [1,2,4]` option.
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The `-t` or `--threaded` options will run the simulated hardware in a separate
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thread from the frontend, which will run as fast as possible, faster than
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real-time. By default, the simulated hardware is run inline with the frontend's
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update cycle, which is limited to 60Hz. The simulation will be run for 16.6ms of
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simulated time for each frame the frontend draws. But the simulated time is not
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accurate and Sega Genesis games will run slower than they should.
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The `-d` or `--debugger` option will make the emulator start the debugger
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before running. There is a simple built-in debugger for stepping through
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the rom instructions being emulated. The state of the CPU registers will
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be displayed after each instruction, breakpoints can be set, memory contents
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can be examined, and memory locations can be modified. This has helped a lot
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with tracking down errors in the emulator itself.
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The `-x` or `--speed` option, when given a decimal number, will multiply that
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number by the milliseconds per frame, increasing or decreasing the gameplay
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clock relative to the frontend's update loop. Setting it to 0.5 slows the game
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down to half speed and setting it to 2 doubles the speed.
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The `-a` or `--disable-audio` option will prevent the audio device from being
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created, so no audio will be played (although it will still be simulated by any
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devices that simulate it).
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