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117 lines
4.8 KiB
Markdown
117 lines
4.8 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 Computie (68000) and the TRS-80 Model I (Z80), and I'm
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working on supporting the Macintosh 512k and Sega Genesis.
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For more detail, 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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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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Sega Genesis/MegaDrive
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----------------------
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It can be run with:
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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 a work in progress. It can play a few games but some
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games won't run because the bank switching for the Z80 coprocessor is not
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working yet, and some games will hang waiting for the Z80 to respond. For the
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video processor, the window layer is not drawn and the layer priority is not
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handled. The horizontal scroll also doesn't work on a line-by-line basis so it
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tends to be quite jerky as you move, with the sprites and cells misaligned
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until you've moved one complete cell over (8x8 pixels).
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On the Sonic 2 title screen, the colours for Tails are wonky, probably because
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there's some trickery going on to get more than 16 colours per line, but the
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emulator currently renders the whole frame at once instead of line by line, so
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changes that should be made while the screen is updating don't show up
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The game play is mostly working but the bottom of the clouds should be a
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different colour, probably because highlight/shadow colours are not yet
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supported. The time in the upper left corner also doesn't seem to progress
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I'm not yet sure why the clouds in the background are cut off suddenly. They
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change in a glitchy way when you move around
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There are some graphics glitches in Earthworm Jim, but it's almost playable if it
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wasn't for the 'jump' button, which only makes him jump a few pixels
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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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