GS FLY

An Apple IIgs pulls real neurons out of the first complete fruit fly connectome and rotates them on a 65C816. Built for the IIgs 40th anniversary, September 15, 2026.

On September 3, 2026, HHMI Janelia and Google Research published MaleCNS v1.0, the first complete wiring map of a fruit fly's entire central nervous system: brain and nerve cord, 166,700 neurons, about 125 million synaptic connections. Twelve days later, forty years to the day after Apple announced the IIgs, this program loads a block of those neurons onto a 2.8 MHz IIgs, spins each one in 3D with depth shading, and keeps a running benchmark of how fast the 65C816 is chewing through the map.

Every number on the screen comes from the data or the tick counter. Nothing is faked.

What you see

1. Title cards at 640x200 in anti-aliased Helvetica Neue and hinted Geneva, palette-faded.
2. Boot console. With a CoGS card in the machine, the IIgs opens a TLS session to a2cogs.com, prints the negotiated TLS version and cipher, and streams the neuron block down through the card with a live progress bar driven by the bytes as they land. Without a card it says so and loads the same block from disk.
3. Viewer. One neuron at a time: real skeleton nodes rotated about Y, depth-shaded through a 12-step ramp, branch terminals marked, soma marked, with the neuron's cell type, a plain-English tag, its bodyId, node count, and presynaptic / postsynaptic site counts from the dataset. Underneath: nodes transformed per second, frames per second, neurons processed, synapses accounted for, and a projection of how long the full 166,700-neuron connectome would take at this rate. The soundtrack starts with the first neuron; M mute in the header turns into U unmute while it is quiet.

(Screenshots are from the headless MAME harness with the virtual CoGS card, which is why the Peer line has no cipher; a real card fills in TLS 1.3 and the suite.)

The data

GSFLY.DATA is 75,418 bytes: 18 neurons of 9 cell types from MaleCNS v1.0, fetched through neuPrint with neuprint-python and navis, then packed by pack_fly.py.

type	what it is	in the block
GF (DNp01)	giant fiber, the escape reflex	2
DNa01, DNa02	descending neurons, brain to nerve cord	4
MBON01, MBON03	mushroom body output, memory readout	4
LC10 (LC10a), LC4	visual projection neurons	4
PPL101	dopamine neuron, reward and punishment learning	2
aMe12	circadian clock neuron	2

Each skeleton is capped at 600 nodes. MaleCNS skeletons run 400 to 13,000 nodes, so the packer prunes the shortest terminal twigs first until 600 remain, keeping root, branch points and the long cable. Coordinates are centered on the centroid and scaled to plus or minus 30,000 as int16. Synapse counts (pre, post) are the dataset's own per-neuron totals, not derived.

FLY1  u16 count
per neuron:
  u32 bodyId   char[16] type   u16 nNodes   u32 pre   u32 post
  int16 x,y,z * nNodes          u16 parent * nNodes  (0xFFFF = root)

How the IIgs does it

• Per-scanline video modes. The IIgs lets each of the 200 scanlines pick 320 or 640 mode and one of 16 palettes. The viewport (rows 10 to 146) is 320 mode with a 16-color depth ramp. Every text row on the screen, and the whole console, is 640 mode with a 4-level palette, drawn with hinted 9-pixel Geneva and Monaco doubled horizontally. Same frame, two resolutions.
• 16-bit rotation. When a neuron comes up it is pre-scaled once into screen units (|x|, |z| <= 126). With a 7-bit sine the per-frame rotation x*cos - z*sin stays inside 16 bits, so the transform is all native int math. The long divides happen once per neuron, not 600 times a frame.
• Segment-interleaved redraw. At one or two frames a second a full erase pass followed by a draw pass would blink. Each segment is erased and redrawn in turn, so the neuron never leaves the screen.
• Real benchmarks. nodes/sec and fps are counted against the 60 Hz tick. Done accumulates neurons after their 12-second dwell (or Space). The "full connectome in N days" line is 166700 / N * elapsed.
• Chrome that does not flicker. Data lines redraw glyph over glyph, then black the tail, so numbers update in place.

Stock IIgs: about 1 frame a second on a 600-node neuron. With an accelerator, two or three.

The music

Low Orbit Bright was written for this demo and plays on the Ensoniq DOC through NinjaTrackerPlus 1.4 (Jesse Blue / Ninjaforce). It starts the moment the first neuron begins to paint, loops for as long as the viewer runs, and stops cleanly on Esc.

• 13 channels, 9 instruments (bowed strings, Unitra organ, electric bass, upright keys, recorded kick, snare, hat, key stab, marimba), 22 patterns, 110 BPM. One pass is 3:12, then it restarts from the top.
• The source is a 13CH Amiga-style MOD. convert_ntp.py is a Python port of the official NTP converter with streaming forbidden, so every sample lives in DOC RAM. It splits the two looped instruments into attack plus loop, which is why the NTP has 11 instruments for 9 samples. The report: 118 of 256 DOC pages used, 19 music oscillators plus the timer oscillator.
• NTPPLAYER is the stock player assembled with Merlin 32. It expects to sit at the start of a bank, so music.c asks the Memory Manager for a whole free bank first and falls back to a fixed address at $0F0000, $0E0000 and so on. ntpcall.c is a 5-byte JSL slot in data that the C side patches before each call.
• The Sound Manager is shut down before NTPprepare so the player owns the sound interrupt vector, and started again on exit so the Finder gets its beep back.
• Play volume is 115 of 255. M sets the player volume to 0 and U puts it back, so the song keeps its place while muted. Only the header label is redrawn, not the frame.

Files on disk: GSFLY.NTP (the song, 102,395 bytes) and NTPPLAYER (34,672 bytes) beside GSFLY. Without them the viewer runs silent and the mute label is not drawn.

The CoGS path

CoGS is a co-processor and network card for the Apple II (RP2350, Wi-Fi, TLS 1.2/1.3 terminated on the card). GS FLY uses the same client library the CoGS Control Panel uses:

1. Scan slots 1 to 7 for the card signature, check the link is up.
2. GET https://a2cogs.com/fly/GSFLY.DATA with Range: bytes=0-31. That one request does DNS, TCP and the TLS handshake on the card, confirms the URL is live, and returns the header (magic, count) that the console prints.
3. TLS_INFO for the Peer line.
4. Stream the full file through the card's FIFO. Every DATA frame moves the bar; the byte count on screen is the transfer.
5. Swap the downloaded block in for the disk copy before the viewer starts.

So if the block on the server changes, the GS renders the new one. The disk copy exists so anyone can run the demo without a card.

Running it

Release images (see Releases):

• gsfly800.2mg: 800K ProDOS floppy, volume /GSFLY800 (so it can sit next to the 32 MB /GSFLY boot volume). Boot GS/OS from anything, mount this, run GSFLY.
• gsfly.2mg: 32 MB GS/OS 6.0.4 boot volume with GSFLY/ on it (also carries the CoGS tools). Boot it from a CFFA, or in Ample as a hard disk, open the GSFLY folder, run GSFLY.

Controls: any key skips the intro. Space next neuron, A toggles auto-advance (12 s), M mutes the music, U unmutes, Esc exits from anywhere, including mid-download.

Tested on Ample (MAME) with ROM 3, and on a ROM 01 IIgs with a CoGS card in slot 3.

Building

Host side needs Python 3 with neuprint-python, navis, numpy, Pillow, and a free neuPrint token in NEUPRINT_TOKEN:

python3 pack_fly.py            # FLYDATA.BIN from MaleCNS v1.0
python3 gen_cards.py           # FLYCARDS.BIN, the three 640-mode title cards
python3 gen_font640.py         # font640.h from Geneva 9 / Monaco 9
python3 gen_boot_shr.py        # FLYBOOT.shr, the console backdrop

GS side is ORCA/C via Golden Gate (occ, iix). build.sh compiles fly.c, music.c, ntpcall.c and the two cogslib files in lib/ (from the CoGS repo, kept at -O0 for the reasons in its Makefile) and inject.sh lays the six GS files onto the disk images with AppleCommander and re-wraps the 2IMG header. python3 convert_ntp.py song.mod GSFLY.NTP rebuilds the song from a MOD. test/run_snap.sh boots the result in headless MAME and screenshots it; MAME_EXTRA="-sl3 cogs" adds the virtual card.

Two ORCA/C notes that cost an evening: pointer + unsigned with a constant long base miscompiles (use a table of row pointers), and a static initializer holding the address of another static array relocates wrong once the link has more than one object file (bind those at run time).

Credits

• MaleCNS v1.0: HHMI Janelia Research Campus and Google Research. Data via neuPrint.
• neuprint-python and navis for the fetch and skeleton handling.
• Console backdrop is a crop of the 1986 The Fly poster, which opened a month before the IIgs shipped.
• NinjaTrackerPlus player and converter by Jesse Blue, Ninjaforce. Instrument recordings in Low Orbit Bright are CC0 sources.
• Rob Perissi, September 2026. MIT license.