Major Havoc (Atari, 1983) for MiSTer FPGA

A MiSTer FPGA core for Major Havoc, Atari's 1983 dual-CPU color-vector maze/action game. There is no Major Havoc core on MiSTer main; this one is built by grafting a new Major Havoc game module onto the proven Star Wars color-vector chassis (Videodr0me/Arcade-StarWars_MiSTer), reusing its DDR3 vector framebuffer, display path, and OSD.

Status (v1): boots and is playable on real DE10-Nano hardware — the maze, the reactor, and the space sequences render; quad-POKEY audio, the roller (analog stick / USB spinner / USB mouse), fire, shield, and coins all work; the game runs at authentic speed (see Authentic speed); and the display is stable (see Vector presentation).

⚠️ ROMs required — not included. This core does nothing without the Major Havoc romset. You must supply mhavoc.zip (MAME mhavoc) in your MiSTer's games/mame/ folder. No ROMs are distributed here (Major Havoc is © 1983 Atari). See Install.

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Why "Star Wars chassis"?

Major Havoc and Star Wars run on closely related Atari Analog Vector Generator (AVG) hardware. Rather than re-implement the hard parts — the DDR3 triple-buffered vector framebuffer, the MISTER_FB scan-out, the clock/CDC plumbing, the OSD — this core hosts a Major Havoc game module inside Videodr0me's Star Wars project and routes its AVG vector output into the same vector_fb_ddram rasterizer that ships in Star Wars.

One consequence: the Quartus project, the top-level entity, and the output bitstream are still named Arcade-StarWars internally. What you flash is renamed to Arcade-MajorHavoc.rbf, and the MRA's <rbf>Arcade-MajorHavoc</rbf> points at it.

What's in this core (vs. the Star Wars chassis it sits on)

New — the Major Havoc game module (rtl/majorhavoc.vhd, rtl/avg/avg_majorhavoc.vhd, rtl/mhavoc_sw.sv), transcribed from MAME's atari/mhavoc.cpp:

• Dual 6502 (T65) — the Alpha CPU (2.5 MHz, main game + AVG) and the Gamma CPU (1.25 MHz, I/O + audio + roller + comms), with the full Major Havoc memory map, the banked program ROM, the banked vector ROM, the alpha/gamma inter-processor comms latches, and the 5 kHz / ~250 Hz IRQ chain.
• Color AVG (avg_majorhavoc.vhd) — a Major Havoc variant of Jeroen Domburg's behavioral Black Widow AVG, centred and color-mapped for MH.
• Quad POKEY audio (4× POKEY summed) on the gamma bus.
• The roller (Major Havoc's 8-bit relative dial) and the coin/service inputs.
• A coordinate map (MH AVG coords → the 980×720 framebuffer, with OSD orientation + scale) and a phosphor-persistence present-gate (rtl/present_gate.sv) — see below.

Reused, unchanged — Videodr0me's Star Wars chassis: vector_fb_ddram.sv (the DDR3 triple-buffer vector framebuffer), the MISTER_FB display path, the sys/ MiSTer framework, clock/CDC plumbing, and the OSD/DIP infrastructure.

Authentic speed

Major Havoc is the odd one out among the Atari AVG games: it used a 10 MHz crystal (Alpha 6502 at 10/4 = 2.5 MHz), whereas Star Wars, Tempest, Black Widow and Gravitar all used the 12.096 MHz crystal the Star Wars chassis runs at. Dropping MH straight onto the chassis therefore ran the whole game (and its audio pitch) ~21% fast.

To fix this without a second clock domain (a separate 10 MHz PLL output corrupts the ROM download across the clock boundary), the game is kept on the 12.096 MHz chassis clock but gated by a clock-enable (game_ce, high 5 of every 6 cycles → effective ~10.08 MHz, +0.8%). The CPUs, AVG, IRQ rate, and POKEY all derive from the gated counters, so everything slows uniformly with the hardware ratios preserved. Sim-verified (the AVG redraw period lands at the authentic rate, geometry identical).

Vector presentation

A real Major Havoc redraws its whole vector display list many times a second, and the CRT phosphor integrates those redraws: any beam a single redraw happens to miss is refilled by the next. A DDR framebuffer has no phosphor, so presenting one redraw per displayed frame exposes every beam the shared-DDR bus drops, and a list cut mid-draw drops its tail.

rtl/present_gate.sv emulates the phosphor: it accumulates N complete AVG lists (each bounded by the CPU's once-per-list vggo strobe) into one draw buffer with no clear between them — a union of N redraws — then presents. Dropped beams get refilled across redraws, and because every accumulated list is complete, no tail is cut. The framebuffer keeps swapping on its own scan-out vblank, so the per-frame clear window is never visible. N is a live OSD knob ("Persistence"). The framebuffer also supports a fast selective-erase path (replay only the drawn pixels as black, ~1 ms vs a ~16 ms full clear) used at the crisp/N=1 setting; verified in simulation (sim/fb/).

Install

1. Copy releases/Arcade-MajorHavoc_<date>.rbf to your MiSTer's _Arcade/cores/ and rename it to MajorHavoc.rbf (keep exactly one MajorHavoc*.rbf there). The MRA's <rbf>MajorHavoc</rbf> matches this name; the firmware ignores any _<date> suffix, so MajorHavoc_20260605.rbf works too. (This matches the MiSTer Distribution layout, where the Arcade- prefix is stripped — see update_all.)
2. Copy releases/Major Havoc.mra to _Arcade/.
3. Required: put the Major Havoc romset mhavoc.zip (MAME mhavoc) in games/mame/. The core will not run without it — the MRA loads the ROMs from this zip. ROMs are not included in this repo or release.

Launch the MRA from the MiSTer arcade menu.

Controls

Input	Action
Roller — left analog stick, or a USB spinner, or a USB mouse (X axis)	Move the ship / steer through the maze
Fire (pad A / mouse left)	Fire
Shield (pad B / mouse right)	Shield
Coin	Insert coin (the game starts on Fire after a credit)

The roller has a velocity-shaped response: gentle for fine aim on slow movement, faster on a quick flick, ported from the tuned Tempest spinner. The analog stick uses a softer curve (more of the throw dedicated to slow/medium speeds). A real spinner or mouse gives the most authentic feel; the analog stick works on any pad.

OSD options

Beyond the standard MiSTer video/scaler options, this core exposes:

• Aspect ratio — Optimized (auto scale to your output) or Pixel Perfect (1:1).
• Rotate / Flip — orientation relative to the built-in baseline.
• Roller Sensitivity — how much the ship moves per unit of roller/mouse/stick motion: Default (the tuned value) / Low (×¾) / Lower (×½) / High (×1½) / Higher (×2). Scales both the velocity step and its per-event clamp; Default matches the previous feel exactly.
• Vector Scale — Fill (1.25×) / Full (1×) / Three-Qtr / Half. Fill is the default; drop it if a scene clips on your display.
• Frame Gate — On (normal) presents via the persistence gate; Off is a native AVG pass-through diagnostic.
• Persistence — how many complete vector redraws are accumulated per displayed frame (12 default, then 14 / 10 / 8 / 6 / 4 / 2 / 1 "Crisp"). Higher = more phosphor-like fill and steadier image; lower = crisper but flickerier (1 = the selective-erase 60 Hz path).

update_all / Distribution

This repo follows the MiSTer external-core layout that theypsilon's Distribution_Unofficial_MiSTer scanner expects, so it can be tracked by update_all:

• The core lives in releases/ as a date-stamped Arcade-MajorHavoc_<YYYYMMDD>.rbf (the scanner skips any un-dated .rbf and always picks the newest date).
• The installer copies it to _Arcade/cores/ stripping the Arcade- prefix → MajorHavoc_<date>.rbf, which is why the MRA uses <rbf>MajorHavoc</rbf>.
• The .mra sits in releases/ and is copied to _Arcade/.

To get it tracked, theypsilon adds one row to that repo's external_mister_repos.csv: https://github.com/derpyder/Arcade-MajorHavoc_MiSTer, _Arcade,,. (Note: that repo's README currently says "No new cores will be added," so acceptance is at theypsilon's discretion — until then, users can add the repo to their own downloader.ini.)

480p @ 120 Hz on a CRT PC monitor

This core can be driven at 480p120 on a multisync CRT PC monitor via MiSTer.ini (no rebuild needed). See docs-480p120-crt.md for the exact settings, the scan-rate math, and the monitor requirement.

Known limitations

• Hi-score persistence is not implemented (the EAROM is stubbed), so scores reset on power cycle.
• Internal project/bitstream identity is Arcade-StarWars (see above).

Building

Quartus Prime 17.0 (Cyclone V / DE10-Nano):

quartus_sh --flow compile Arcade-StarWars
# -> output_files/Arcade-StarWars.rbf  ->  rename to Arcade-MajorHavoc.rbf

Simulation lives in sim/ (ModelSim ASE framebuffer / present-gate tests) and a GHDL render/cadence testbench under ../Arcade-MajorHavoc/sim/. See HANDOFF-mhavoc-sw.md for the sim recipes and design history.

Credits & license

This core stands on a lot of prior work:

• Videodr0me — the Star Wars MiSTer port and the vector_fb_ddram DDR3 vector framebuffer chassis this core is built on.
• Jeroen Domburg (Sprite_tm) — the behavioral Black Widow AVG that avg_majorhavoc is derived from.
• T65 / POKEY authors and the broader MiSTer/MAME communities — the Atari vector hardware lineage and reference models.
• MAME — the authoritative Major Havoc memory map and hardware behavior.

Original code is GPLv3 (see COPYING); third-party modules retain their own licenses (see file headers and LICENSES). This is a non-commercial, preservation-oriented project and is not affiliated with Atari.