Tempest (Atari, 1981) for MiSTer FPGA

A MiSTer FPGA core for Tempest, Atari's 1981 color-vector tube shooter. There is no Tempest core on MiSTer main; this one is built by grafting a new Tempest game module onto the proven Star Wars color-vector chassis (Videodr0me/Arcade-StarWars_MiSTer), reusing its DDR3 vector framebuffer, display path, audio chain, and OSD.

Status: boots and is playable on real DE10-Nano hardware — fire, superzapper, coins, audio, and a stable flicker-free display all confirmed, and the picture fills the screen with clean integer scaling up to 4K (see Vector presentation). Rotation is confirmed on hardware via both the analog stick and a USB mouse / spinner (velocity-sensitive, with an OSD direction toggle) — see Controls.

⚠️ ROMs required — not included. This core does nothing without the Tempest romset. You must supply tempest.zip (MAME tempest) in your MiSTer's games/mame/ folder. No ROMs are distributed here (Tempest is © 1981 Atari). See Install.

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Why "Star Wars chassis"?

Tempest 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, clock/CDC plumbing, the OSD — this core hosts a Tempest 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-Tempest.rbf, and the MRA's <rbf>Arcade-Tempest</rbf> points at it.

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

New — the Tempest game module (rtl/tempest.vhd, rtl/avg/avg_tempest.vhd, rtl/tempest_sw.sv):

• 6502 (T65) CPU with Tempest's memory map, transcribed from MAME's atari/tempest.cpp — program ROM/RAM, vector RAM (4K) + vector ROM (4K), the 16-entry color RAM at $0800, IN0/DSW decode, coin/flip latches, and the ~250 Hz IRQ.
• Color AVG (avg_tempest.vhd) — a Tempest variant of Jeroen Domburg's behavioral Black Widow AVG, with Tempest's color-RAM lookup and X/Y handling.
• 2× POKEY audio, the spinner (read through POKEY 1's pot lines), the Atari math box (shared Battlezone/Red Baron/Tempest behavioral model), and the EAROM stub.
• A coordinate map (Tempest tube → the 980×700 framebuffer) and a phosphor-persistence vector 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.

Vector presentation — the flicker fix

A real Tempest redraws its whole vector display list ~200–250 times a second, and the CRT phosphor integrates those redraws: any beam a single redraw happens to miss is refilled by the next, and fast objects leave a soft trail. That integration is what makes a real tube look rock-steady.

A DDR framebuffer has no phosphor, so presenting one redraw per displayed frame exposes every beam the shared-DDR bus drops (intermittent dropped beams when idle) and any list cut mid-draw drops its tail (flashing projectiles when firing).

rtl/present_gate.sv emulates the phosphor: it accumulates N complete AVG lists (each bounded by the CPU's once-per-list vggo/$4800 strobe) into one draw buffer with no clear between them — a union of N redraws. Dropped beams get refilled across redraws (no idle flicker), and because every accumulated list is complete, the projectile tail is never cut (no firing flash). 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") so you can dial the amount of ghosting on hardware. The fix is verified in simulation (sim/fb/tb_gate2.sv).

Install

1. Copy releases/Arcade-Tempest_<date>.rbf to your MiSTer's _Arcade/cores/ and rename it to Tempest.rbf (keep exactly one Tempest*.rbf there). The MRA's <rbf>Tempest</rbf> matches this name; the firmware ignores any _<date> suffix, so Tempest_20260602.rbf works too. (This matches the MiSTer Distribution layout, where the Arcade- prefix is stripped — see update_all.)
2. Copy releases/Tempest.mra to _Arcade/.
3. Required: put the Tempest romset tempest.zip (MAME tempest, the Rev-3 parent set) in games/mame/. The core will not run without it — the MRA loads the ROMs from this zip and lists the exact CRCs it expects. ROMs are not included in this repo or release.

Launch the MRA from the MiSTer arcade menu.

Controls

Tempest's tube is controlled by a knob (a 4-bit up/down encoder in the real hardware). This core feeds that knob from any of three sources, in priority order:

Input	Action
Spinner / paddle (USB)	Rotate around the tube — the authentic control
USB mouse (move L / R)	Rotate (same path as a spinner; velocity-sensitive)
Left analog stick	Rotate (rate-proportional: full throw = fast, feather = fine)
D-pad ← / →	Rotate (fixed rate)
Fire / mouse left btn	Fire
Superzapper / mouse right btn	Superzapper (screen-clear, limited)
Start 1P / 2P	Start
Coin	Insert coin

Spinner / mouse: rotation is velocity-sensitive — small movements nudge the tube one notch at a time, faster movements spin proportionally faster, all kept within the game's 4-bit knob decode so the direction is always correct at any speed. The path is confirmed on hardware with a USB mouse (which is how most USB spinners enumerate). If your spinner turns the wrong way, flip Spinner Reverse in the OSD. Dedicated spinner devices feed the same internal stepper; if yours needs a tweak, please report back.

OSD options

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

• Aspect ratio — Optimized (auto integer scale: the 980×720 frame is scaled ×1/×1.5/×2/×3 to best fit your output — ×3 fills 4K vertically exactly) or Pixel Perfect (1:1). The vector image is drawn to fill the frame either way.
• Rotate / Flip — orientation relative to the built-in baseline, for portrait cabinet monitors.
• 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 (3 default / 4 / 6 / 2). Higher = more phosphor-like ghosting/trails and more resistance to dropped beams; lower = crisper but flickerier.
• Spinner Reverse — flip the spinner/mouse rotation direction (Off / On), so a clockwise turn of your device matches clockwise on the tube.
• Spinner Sensitivity — how much on-screen rotation you get per unit of spinner/mouse movement: Default (the tuned value) / Low (×½) / Lower (×¼) / High (×1) / Higher (×1½). This scales the input gain only; the direction-safe pacing that keeps fast spins from reversing is unchanged, so all settings stay direction-correct.

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-Tempest_<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 → Tempest_<date>.rbf, which is why the MRA uses <rbf>Tempest</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-Tempest_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-Tempest_<date>.rbf

Simulation lives in sim/ (ModelSim ASE present-gate / framebuffer tests) and the GHDL boot/cadence testbench. See HANDOFF-tempest-sw-resume.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_tempest is derived from.
• Dave Wood / fpgaarcade / alanswx and the broader MiSTer/MAME communities — the Atari vector hardware lineage, T65, POKEY, math box, and reference models.
• MAME — the authoritative Tempest 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.