NSPacMan

A Pac-Man–style arcade game for the NorthStar Advantage (1982) — written from scratch in Z80 assembly.

It boots bare-metal from the Advantage's stock boot PROM — no CP/M, no DOS — and runs identically on the NorthMac emulator and on real hardware, loaded from a USB stick via a Gotek floppy emulator. The whole game is under 6 KB: it fits, with its loader, in the first two tracks of one hard-sectored floppy — and it saves its high-score table back to that same floppy.

Features

• The classic 28×31 maze (240 dots, 4 power pills) rendered as thin arcade-style outline walls, context-derived from the maze data
• Horizontally doubled 16×8 sprites and tiles — on the Advantage's tall CRT pixels this lands almost exactly on arcade proportions
• Four ghosts with staged house release, chase AI with per-ghost personality, frightened mode, and chain scoring (200/400/800/1600 shown frozen at the meal spot, arcade-style)
• Flashing power pills, chomping animation, collapse-and-pop death sequence
• Sound on the Advantage's 1-bit speaker: intro fanfare, waka-waka, power-pill sweep, rising ghost-eat zip, death warble with final bleep-bleep (all original renditions in the arcade spirit)
• SCORE and HIGH panel and lives in an arcade-style 8×8 font
• Bonus life at 10,000 points; a musical intermission plays after every second maze cleared
• Attract mode: title screen with a ghost parade alternating with the top-10 table; any key starts a game
• High scores: a qualifying score prompts for three typed initials. The top-10 table is written back to the floppy (track 4, sector 5 — an otherwise-empty track, two guard tracks away from any code) using the technical manual's §3.7.7 write protocol, so scores survive power-off — on real hardware the Gotek persists them into the HFE on the USB stick. On a write-protected disk scores simply live in RAM until power-off.
• Steering: WASD, IJKL, keypad 8/4/6/2, or the keypad arrow keys (^H ^J ^K ^L control codes); ESC restarts mid-game

Building

Requires z80asm (brew install z80asm) and Python 3.

./build.sh          # -> pacman.nsi (NorthStar sector image)
./build.sh hfe      # -> pacman.hfe (Gotek/HxC HFEv3, needs greaseweazle)

Run it in NorthMac:

northmac pacman.nsi     # press RETURN at LOAD SYSTEM

Running on real hardware

The Advantage uses hard-sectored floppies (ten sector holes plus an index hole; sector identity is purely positional), which rules out ordinary floppy-emulator images. The path that works:

1. A Gotek running HxC firmware (hard-sector support), S0 jumper only
2. Disk images in HFEv3 (SETINDEX opcodes carry the sector pulses) — build.sh hfe produces one via greaseweazle's native North Star codec
3. Name it DSKA0000.HFE (indexed mode) on the USB stick, boot, press RETURN

The two-stage loader talks to the Advantage's floppy controller using a protocol reverse-engineered from the boot PROM and a working CP/M loader, honoring several behaviors of the real silicon that no emulator modeled: the I/O-control register's bit 4 must stay set, the motor timer needs periodic command-5 events, an acquire delivers sector STAT2+1, and the sector-number register must never be read mid-stream. The high-score save follows the manual's write protocol: find the prior sector, catch the sector-mark edge, arm the write flag within 150 µs, then stream preamble, sync bytes, 512 data bytes, and a software CRC. The full contract is documented in the NorthMac project.

test/run_full.c is a headless full-system harness: it boots the actual disk image through the loader against a faithful floppy-controller model (including hardware-correct sector writes), injects scripted keystrokes, and can cold-boot a second time to prove the high-score table persisted.

Provenance

Inspired by Hans Hübner's Advantage resurrection, in which he concluded that "the NorthStar Advantage never had a chance to shine as a gaming system until now." This is an independent take on the same idea: the game, its graphics, and its sounds were written from scratch (with Claude Code as the co-author) in one long day, on a boot-and-graphics foundation built while porting the GREENFIELD generative-art demo to real hardware.

PAC-MAN is a trademark of Bandai Namco Entertainment. This is an unaffiliated fan homage with original code, art, and audio, built for the joy of seeing a 1982 business machine finally get to play.