Oh My God! / Naname de Magic! (Atlus) for MiSTer

Atlus' Oh My God! (1993) and Naname de Magic! (1994), the two games of MAME's atlus/ohmygod.cpp driver (68000 at 12 MHz, one OKI M6295, one 64 x 64 tile layer and 1024 sprites), for the MiSTer FPGA platform.

Written for MiSTer from MAME 0.289's driver. The 68000 is fx68k (Jorge Cwik), the OKI M6295 is jt6295 (Jose Tejada), the CRT Adjust page is rmonic79's MiSTer-CRT-Adjust. The platform layer (SDRAM controller, loader, program cache) is the owner's, from the MCatAdv and Metro cores; the SDRAM controller descends from the Gaiapolis core that plasticbugs wrote for the Analogue Pocket (rtl/UPSTREAM.md, modules/VENDOR.md). No ROMs or other copyrighted data are in this repository; you supply your own MAME romsets.

Status

Tested on a real MiSTer by the repository owner: the picture, the sound, the controls and the OSD options (20261010), and the new features of 20261023 (fast loading, Scale, named buttons) and, in 20261023b, the Flip Screen of Naname de Magic!, which did not flip in 20261023 and now does. 20261023b also removes Service and Test from the button mapping.

What was checked besides, in simulation and in the Quartus tool flow, against MAME 0.289 (details and numbers in docs/status.md):

• The ROM path: both sets' images are byte-identical to the regions MAME loaded (tools/omg_rom.py check), and the MRAs assemble to the same images (tools/mra_build.py).
• The video, against a reference renderer (tools/omg_ref.py) that is MAME's screen_update written out literally: pixel-exact on 120 MAME frames of scripted play (both games), including the busiest frames (179 sprites on screen); the RTL's frozen-state bench (sim/bench/corpus_rtl.sh) against the same MAME pixels: 60 of 60 states per game identical.
• The whole machine from reset (68000, cache, SDRAM controller, cold-start watchdog reset) with MAME's inputs replayed: frames 230 and 280 of both games pixel-identical.
• The sound path against MAME's own OKI samples: same samples, MAME's level (x16), residual 0.01 %.
• The real MiSTer top (sim/emu/, with hps_io and the PLL stubbed): the image loaded the fast way in 0.135 s (every word in the SDRAM), the machine then run through the real 3 s cold start and compared with MAME (frames 230 and 280 of both games pixel-identical); the joysticks and the keyboard reach exactly their bits of the board's ports; the size asked of the HDMI scaler by all 60 Scale / Aspect ratio / scaler size combinations tried; the scandoubler's raster; CRT Adjust on at zero = off, to the clock.
• The Flip Screen DIP of Naname de Magic!: the game's own data (MAME does not emulate the hardware's flip) give MAME's normal picture exactly once the flip's fixed offsets are taken out; the core's flipped picture equals that picture turned 180 degrees on 16 of 16 game states, in the reference renderer and in the RTL.
• Quartus Prime Lite 17.0 compiles the design without errors, timing met.

Install

1. Put releases/ohmygod_YYYYMMDD.rbf in /media/fat/_Arcade/cores/ and the two .mra files of mra/ in /media/fat/_Arcade/ (or unzip the release zip over the root of the SD card). Keep the RBF's ohmygod_ name and date: MiSTer finds the core by the MRA's <rbf> name plus the date. Use the MRAs of the same release as the RBF, and delete older ohmygod_*.rbf files.
2. Put your MAME 0.289 ohmygod.zip and naname.zip in /media/fat/games/mame/.
3. Start a game from the Arcade menu. With a recent Main_MiSTer the 3.6 MB ROM image loads in a fraction of a second (fast loading: the MRAs carry address="0x32000000", which makes Main_MiSTer copy the whole image into the DDR3 at once, and the core plays it from there into the SDRAM); an older Main_MiSTer ignores the attribute and streams the image as before, which takes a few seconds. A cold start shows a grid-patterned / black screen for 3 seconds before the ATLUS logo: the game fills its RAM, writes a signature and waits for the watchdog to reset it (MAME does the same, with the same 3 s). The OSD's Reset keeps the RAM, so the signature survives it and the game restarts without the wait.
4. Buttons: if you mapped the controller with an earlier build, redo "Define joystick buttons" (the list now names the game's action; the Service and Test entries of 20261023 are gone again), or delete this core's *_input_*.map files in /media/fat/config/inputs/.

Controls

One joystick and one button per player, Start and Coin each. MiSTer's button mapping names them by what they do (the names come from the MRA):

Button	Oh My God!	Naname de Magic!	Default on a gamepad
first	Drop: the falling chain falls faster (it does what Down does, and nothing while the chain is swung sideways)	Rotate: turns the falling piece	A
Start, Coin	Start, Coin	the same	Start, Select

The joystick moves the piece (in Oh My God! left / right swing the chain to that side). The keyboard has MAME's defaults: 1 / 2 start, 5 / 6 coin, 9 service (a service credit, MAME's Service 1) and F2 test (the game's test menu, MAME's Service Mode: monitor, switch and sound tests and the DIP switch list; in it the 1P Start button selects and F2 returns to the menu). The two are separate switches on the board and the program treats them differently; they are keys only, not in the button mapping.

OSD

• Aspect ratio, Scandoubler Fx: the framework's.
• Scale: Normal, V-Integer, HV-Integer, Narrower HV-Integer, HV-Integer+: integer scaling on the HDMI scaler (the framework's video_freak). With Aspect ratio Full Screen an integer Scale is given the screen's own proportions, so the picture is a whole-number size in the screen's aspect.
• CRT Adjust (H-Size, H-Position, V-Shift): for the 15 kHz output, through rmonic79's line buffer; the horizontal sync stays native so the CRT keeps its lock. It does nothing while the scandoubler is in use (Scandoubler Fx, or forced_scandoubler in MiSTer.ini).
• DIP switches: the MRA's, per game (coinage, difficulty, VS matches per credit, demo sounds, "Balls Have Eyes" / flip screen, test mode / freeze). Naname de Magic!'s Flip Screen turns the whole picture, tiles and sprites, through 180 degrees: the game then sets bit 14 of the sprite bank register (which MAME ignores, so MAME's picture of it is broken) and writes its scroll words and sprite positions moved by fixed amounts; taking those out gives MAME's normal picture exactly, and the core turns that picture (docs/hardware.md).
• Volume: Normal is MAME's level (the OKI's output is exactly 16 times jt6295's 14-bit sum of voices, clipped to 16 bits; fitted against MAME's own samples, residual 0.01 %), then 6 / 12 / 18 dB lower.
• Sprite bank flip: from the IRQ at the start of vertical blank the game builds the next sprite list into the hidden half of the sprite RAM and flips the bank flag about 46 line times later, i.e. at line ~30 of the picture (Naname: 31, or 45 / 46 in some scenes) while the picture is being drawn. Live (default) lets the flag act at once, as a chip that reads it live would: the previous list above the flip line, the new one below it (so the sprites are in step with the scroll registers the game writes at the same IRQ). At vblank samples the flag at the start of vertical blanking: the whole next frame shows the previous frame's list. MAME, drawing a frame at its end, shows the new list throughout. The two differ by one frame (16.7 ms) of sprite timing and are hard to tell apart by eye; the board's real behaviour is not known. On MAME's own states (tools/omg_bank_effect.py) At vblank differs from MAME's picture in 18 of 60 sampled frames of Oh My God! and 35 of Naname de Magic! (typically about 1 % of the pixels, only while sprites move; at most 13 %, on a scene change), Live in 7 and 10 to 18 (at most 1,111 px; only in the lines above the flip).
• SDRAM read capture: a diagnostic for SDRAM modules that answer late.

Timing

96 MHz machine clock; 68000 12 MHz (/8), OKI 2 MHz (/48), dot clock 6 MHz (/16); 384 x 260 total, 320 x 240 visible, 60.096 Hz, 15.625 kHz. MAME's own totals are 512 x 256 at exactly 60 Hz; the board's real timing is not known.

Build

Quartus Prime Lite 17.0 (MiSTer's toolchain): open OhMyGod.qpf or quartus_sh --flow compile OhMyGod. The MRAs are written by python tools/make_mra.py.

Simulation (Verilator 5 in WSL)

sim/run.sh <image> <frames> <out> +state=<MAME state prefix> +first=2          # one frozen state, vs MAME's pixels
sim/run.sh <image> <frames> <out> +inputs=<replay> +every=50 +first=49 +wav    # the whole machine from reset

tools/lua/dump_state.lua makes the states and the replay inputs with MAME 0.289 (see its header); tools/omg_ref.py, tools/omg_diff.py, tools/omg_corpus.py, tools/omg_cmp.py compare.

sim/emu/run_emu.sh <image> is the end-to-end bench of the real MiSTer top (OhMyGod.sv, with hps_io and the PLL stubbed and a behavioural SDRAM and DDR3 on the pins): it loads the image streamed or the fast way (FAST=1), compares the SDRAM with the image, checks how the joysticks and the keyboard reach the board's ports (BTN=1), the raster with the scandoubler on (FX, FSD), CRT Adjust (CRT), the size asked of the HDMI scaler for every Scale / Aspect ratio setting (SCALEMATRIX=1), and writes the pictures of chosen MAME frames (PICS=230,280) for tools/omg_cmp.py. Its header lists the options.

sim/bench/ holds the scripts that run the whole chain: MAME's dumps (mame/run_states.sh, run_replay.sh, run_sr.sh; set MAME_EXE and ROM_PATH), the ROM check (check_rom.sh, mra.sh; ROM_DIR is the romset folder), the reference renderer (ref.sh, corpus.sh), the RTL's frozen-state corpus (corpus_rtl.sh), the whole machine from reset (sysbench.sh, sysbench_sb.sh for the sprite bank option) and the sound (snd.sh, snd3.sh, with tools/omg_oki_fit.py). They expect a scratch folder work/ next to the repository (MAME's dumps and the ROM images; never committed).

Release

python tools/release.py copies a finished build into releases/ with its fitter / timing / RAM-depth reports; python tools/package.py writes dist/OhMyGod_MiSTer_<date>.zip (the SD card structure: _Arcade/*.mra, _Arcade/cores/*.rbf; no ROMs).

Credits

fx68k (Jorge Cwik), jt6295 (Jose Tejada), MiSTer-CRT-Adjust (rmonic79), the Pocket Gaiapolis core's SDRAM controller (plasticbugs), the MiSTer framework (Sorgelig and contributors), MAME (Nicola Salmoria wrote the Atlus driver).

Licence

GPL-3.0-or-later (fx68k and jt6295 are GPL-3.0).