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LoopyDOOM

★ 40 Open GitHub ↗

An unofficial DOOM port for the Casio Loopy based on GBADoom

// repository documentation

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# LoopyDOOM

A sloppy unfinished port of **DOOM** to the **Casio Loopy** — a 1995 Japanese console built around a Hitachi
SH-1 at 16 MHz, big-endian, with about 512 KB of RAM and a built-in thermal sticker printer.
Requires the [Floopy Drive](https://github.com/partlyhuman/loopycart) flashcart if you want to run this on actual hardware.

This is the real engine, not a reimplementation: id's DOOM by way of PrBoom and GBADoom, with
a new hardware backend for the Loopy's VDP, timers, gamepad, and sound chip.

Disclaimer: This is very unpolished. Really more of a tech demo than a finished product

Featured in https://www.youtube.com/watch?v=nDe06uY5C40

## Status

| | |
|---|---|
| Maps | E1M1 – E1M6 (as much as I could fit in 4MB of ROM)  |
| Video | 8bpp VDP bitmap layer, double-buffered |
| Music | uPD937 synth over SCI1 MIDI, all six maps |
| Sound effects | PCM, played by the cartridge's RP2040 — needs the companion firmware and a DAC |
| Screenshot printing | Options menu → prints the current frame on the console's thermal printer (if it doesn't jam, of course!!) |
| Performance | roughly 8-15 fps on hardware; runs way faster in [LoopyMSE](https://github.com/PSI-Rockin/LoopyMSE) |

## Lineage

id Software's **DOOM** → **PrBoom** → **[GBADoom](https://github.com/doomhack/GBADoom)**
(doomhack) → **LoopyDOOM**.

The portable engine and much of the tree come from GBADoom. The Loopy hardware backend lives
under `platform/`, the boot and link glue under `boot/` and `casloopy.ld`, and the build-time
WAD, music, and SFX bakers under `tools/`. HUD and menu graphics use Kippykip's
GBADoom-custom lumps.

## Requirements

- An **SH-1 big-endian `sh-elf` GCC toolchain** (`--target=sh-elf --with-cpu=m1 --with-endian=big`).
  A Dreamcast SH-4 toolchain will *not* work: it is little-endian and rejects `-m1`. The SH-1 has
  no divide instruction, so GCC emits `__sdivsi3` / `__mulsi3` calls that must resolve from an
  `-m1 -mb` libgcc.
- **`doom1.wad`** — the DOOM shareware IWAD.
- **`gbadoom.wad`** — Kippykip's GBADoom lumps, for `STGANUM0`–`9` (narrow HUD digits; the wide
  `STTNUM` font overruns the small status bar) and for `M_ARUN` / `M_GAMMA` (options-menu items
  GBADoom added). Without the latter two, the OPTIONS menu crashes in `W_GetNumForName`.
- **Python 3**, for the bakers.

Neither WAD is distributed here. See [NOTICE](NOTICE).

## Build

```sh
LOOPY_TOOLCHAIN=/path/to/sh-elf/bin make
```

or put `sh-elf-gcc` on your `PATH` and just `make`. There is no default toolchain path — it is
machine-specific.

Point the build at your WADs if they are not at the default relative locations:

```sh
make WAD=/path/to/doom1.wad MERGE_WAD=/path/to/gbadoom.wad
```

This produces **`rom.bin`** (native big-endian — this is the one you want) and `rom.swap.bin`
(byte-swapped, for tools that expect it). `make dump` prints the size and the first 16 bytes,
which should begin `0E 00 00 80`.

The first build is slow: it bakes the WAD into a multi-megabyte C array and compiles it.
Objects are cached per file, so incremental builds skip that.

### Build options

| Variable | Effect |
|---|---|
| `SERIAL_LOG=1` | Frame timings and `lprintf` output over SCI0 at 38400 baud |
| `DEV_WARP=N` | Boot straight into `E1M<N>`, skipping title and menu. Also binds **D** to warp to the next map |
| `NO_MUSIC=1` | Compile out the uPD937 sequencer entirely |
| `NO_SFX=1` | Compile out the SCI0 sound-effect command frames |
| `PRINT_DEBUG_PREVIEW=1` | The printer isn't emulated; blit what the BIOS *would* print to VRAM and halt |
| `ROMSIZE`, `SRAMSIZE` | Default `4M` / `8K`, matching the Floopy Drive. The linker errors on overflow |
| `WADFLAGS` | Passed to `tools/bake_wad.py` — which maps to keep, what to cull |

One caveat on `SERIAL_LOG`: it samples the SH-1's 16-bit ITU counter thousands of times per
frame, which masks any bug involving that counter wrapping (it wraps every 32.768 ms). If you
are chasing a timing problem, test a plain build.

## Running

**Emulator.** [LoopyMSE](https://github.com/PSI-Rockin/LoopyMSE) runs `rom.bin` directly. It
needs a console BIOS dump, which you must produce from your own hardware. Note that its
renderer does not model the VDP's per-scanline sprite limits, so a clean frame in the emulator
does not prove the absence of a hardware rendering glitch.

**Hardware.** Flash `rom.bin` — not `rom.swap.bin` — to a Floopy Drive with its own flashing
tool. The cartridge must be **ejected from the console** while you flash: a seated console
loads the shared cart data bus and every flash read returns zero, even with the console
powered off.

## Controls

| Button | In game | In menus and the automap |
|---|---|---|
| D-pad | Move and turn | Navigate; pan the automap |
| **A** | Use / open, and run while held | Confirm; toggle automap follow |
| **B** | Fire | — |
| **L** / **R** | Strafe left / right | Zoom the automap out / in |
| **A** + **R** | Next weapon | — |
| **A** + **L** | Previous weapon | — |
| **C** | Toggle the automap | — |
| **D** | Warp to next level (DEV_WARP only)
| **START** | Menu | Back out |.

## Sound

**Music** is real MIDI. DOOM's music lumps are MUS-format, so `tools/bake_music.py` decodes
them and emits note tables for the Loopy's **uPD937** synth. An ITU timer interrupt clocks
those out over SCI1 at 31250 baud — the synth's MIDI input. Sequencing runs on that interrupt
rather than in the render loop, since a frame takes far longer than a MIDI tick.

The uPD937's presets are Casio's own set, *not* General MIDI, so MUS program *N* has nothing
to do with GM instrument *N*; the mapping was chosen by ear, per song. The synth also ignores
note-on velocity — a note is simply on or off — so the ROM already drives it as loud as it
goes, and the Loopy's quiet output is a trait of its analog stage rather than something
software can fix.

**Sound effects** cannot come from the uPD937, which has no PCM path. Instead the SH-1 sends
short command frames over SCI0 to the cartridge's RP2040, which mixes eight voices of DOOM's
PCM lumps and plays them through an I2S DAC. This needs the firmware under `firmware/` and a
PCM5102A wired to the RP2040 — see [`firmware/NOTICE`](firmware/NOTICE) and
`firmware/pico/audio.h` for the wiring. Without that hardware the game is silent apart from
music; build with `NO_SFX=1` to drop the transmit cost.

## Layout

```
boot/         crt0, ROM header, interrupt vectors
casloopy.ld   linker script (ROM at 0x0E000000, entry 0x0E000480)
platform/     Loopy backend: VDP video, ITU timing, input, music, SFX, printer, serial
source/       DOOM engine, from GBADoom
include/      DOOM headers, from GBADoom
tools/        build-time bakers: WAD, music, SFX
firmware/     RP2040 companion firmware for PCM sound effects
```

## License

GPL v2 or later, inherited from DOOM / PrBoom / GBADoom, with per-file copyright headers
retained. See [LICENSE](LICENSE) for the full text, and [NOTICE](NOTICE) for provenance —
including which id Software assets this repository does and does not distribute.

LoopyDOOM

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