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 all behave as they should.

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 %.
• Quartus Prime Lite 17.0 compiles the design without errors; timing met (+1.4 ns at 96 MHz), 27 % of the ALMs.

Install

1. Put releases/ohmygod_YYYYMMDD.rbf in /media/fat/_Arcade/cores/ and the two .mra files of mra/ in /media/fat/_Arcade/. Keep the RBF's ohmygod_ name and date: MiSTer finds the core by the MRA's <rbf> name plus the date.
2. Put your MAME 0.289 ohmygod.zip and naname.zip in /media/fat/games/mame/.
3. Start a game from the Arcade menu. The ROM takes a few seconds to load. 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.

Controls

One joystick, one button per player; the keyboard has MAME's defaults (1 / 2 start, 5 / 6 coin, 9 service). The OSD's Button, Start, Coin, Service follow the MRA's <buttons>.

OSD

• Aspect ratio, Scandoubler Fx: the framework's.
• 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.
• DIP switches: the MRA's, per game (coinage, difficulty, VS matches per credit, demo sounds, "Balls Have Eyes" / flip screen, test mode / freeze).
• 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/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).