Rope: the Apollo Guidance Computer, taken apart

README.md

@@ -11,6 +11,7 @@ the same model that moves the parts. Left alone, each page plays a guided tour;
 
 | | The machine | What drives it | Checked by |
 |---|---|---|---|
+| [**Rope**](machines/rope) | The Apollo Guidance Computer Block II and its DSKY, as flown in Apollo 11's lunar module: a word read from the core rope (a wire through a core is a 1, around it a 0), an erasable core read and rewritten, one kind of NOR gate, the Executive running out of core sets as the rendezvous radar steals cycles, the 1202. A model after public sources (MIT Instrumentation Lab, NASA); not affiliated with NASA or MIT. | The mission time, counted in memory cycles since PDI. The Executive's log (jobs, priorities, radar steals, the crew's keys) is planned once. | `machines/rope/check.mjs` |
 | [**Quantum**](machines/quantum) | A photonic quantum computer: a quantum dot emits one photon per laser pulse, fibre delay lines bring them onto a 24-mode chip together, 276 Mach-Zehnder interferometers mix them, superconducting detectors click. A Hong-Ou-Mandel test on one coupler, the Perceval program behind the heaters. Modelled on the public figures of Quandela's Belenos; not affiliated with Quandela. | The physical time τ of the shot, in nanoseconds. The output distribution is computed from the permanents of the chip's unitary. | `machines/quantum/check.mjs` |
 | [**Spindl**](machines/spindl) | A 3.5-inch 7,200 rpm desktop hard drive (2 platters, 4 heads): spin-up, the heads loading off the ramp, a seek drawn live, the rotational wait, the 3 nm flying height, the emergency park. A model of a typical drive, not a specific product. | The drive time τ. A request queue (LBA → zone, cylinder, head, sector) is planned once. | `machines/spindl/check.mjs` |
 

machines/rope/FILM.md

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+# The film
+
+The tour (40 s) is recorded frame by frame from `machines/rope/agc-film`, the same code as the page, with the capture
+tools of the teardown skill ([whaleyxbt/claude-motion](https://github.com/whaleyxbt/claude-motion)). They need the
+skill installed (`SKILL_DIR`), headless Chrome with a real GPU, `ffmpeg` and Python 3.
+
+```sh
+cd machines/rope
+node agc-shared/make-timeline.mjs                       # agc-film/timeline.json (beats) and sfx.json (keys, alarms, calls)
+node "$SKILL_DIR/sims/build.mjs" ./agc-film
+echo '{"lang":"en"}' > teardown-out/en.json             # or fr / es
+node "$SKILL_DIR/sims/capture.mjs" agc-film --timeline agc-film/timeline.json --config teardown-out/en.json --size 1600x900 --dpr 1.2 --stills beats --cols 4 --out teardown-out/beats.png
+node "$SKILL_DIR/sims/capture.mjs" agc-film --config teardown-out/en.json --size 1600x900 --dpr 1.2 --out teardown-out/silent.mp4
+python3 "$SKILL_DIR/run_sfx.py" agc-shared/score.py     # teardown-out/rope-score.wav, mastered to −14 LUFS
+ffmpeg -y -i teardown-out/silent.mp4 -i teardown-out/rope-score.wav -map 0:v -map 1:a -c:v copy -c:a aac -b:a 256k -shortest -movflags +faststart teardown-out/rope-en.mp4
+```
+
+The share card is the film's first frame, scaled: `ffmpeg -y -i teardown-out/rope-en.mp4 -frames:v 1 -vf "crop=1920:1008:0:36,scale=1200:630" -map_metadata -1 og.png`.
+
+On macOS, Playwright's headless shell may get no WebGL context; point the capture at Chrome:
+`CHROMIUM="/Applications/Google Chrome.app/Contents/MacOS/Google Chrome"`.
+
+`{"lang":"en","clean":true}` records the machine without the console.

machines/rope/REFERENCES.md

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+# Rope: references
+
+Rope is a model of the Apollo Guidance Computer Block II and its DSKY, as flown in the lunar module of Apollo 11
+(Luminary 099), built from public sources: the MIT Instrumentation Lab's documents and code as preserved by the
+Virtual AGC project, NASA's mission records, and the restoration work of Ken Shirriff and Marc Verdiell. It is not
+affiliated with NASA, MIT or Draper. Where a figure is not public or could not be found, the model uses a plausible
+value and marks it `[E]` below and in [`agc-shared/machine.js`](agc-shared/machine.js), where every number lives.
+
+## Sources
+
+- **[W]** [Apollo Guidance Computer](https://en.wikipedia.org/wiki/Apollo_Guidance_Computer), Wikipedia, and the
+  documents it cites: 16-bit word (15 data bits + odd parity), ones' complement, 36,864 words of core rope and 2,048
+  of erasable core, 2.048 MHz clock, 11.72 µs memory cycle, ~2,800 flat-packs of dual 3-input NOR gates, 32 kg
+  (70 lb), 55 W, 61 × 32 × 17 cm (24 × 12.5 × 6.5 in), green electroluminescent seven-segment digits.
+- **[S]** Ken Shirriff, [Software woven into wire: core rope and the Apollo Guidance Computer](https://www.righto.com/2019/07/software-woven-into-wire-core-rope-and.html)
+  (2019): 6 rope modules of 6,144 words, 512 cores each (two layers of 256), 12 words per core on 192 sense lines
+  (12 strands of 16), inhibit lines that select one core, set and reset pulses, a wire through the core reads 1 and
+  a wire around it reads 0; the photographs of the opened AGC (trays A and B), of tray B's modules B7-B17, of the
+  inside of a rope module, and the simplified rope diagram the geometry was built against.
+- **[L]** Luminary 099 (Apollo 11 LM), as transcribed by the [Virtual AGC project](https://www.ibiblio.org/apollo/)
+  ([listings](https://www.ibiblio.org/apollo/listings/Luminary099/), [chrislgarry/Apollo-11](https://github.com/chrislgarry/Apollo-11)):
+  - `EXECUTIVE.agc`: NOVAC2, NOVAC3, NEXTCORE, and `TC BAILOUT1` / `OCT 1202`; the assembled words and their
+    addresses shown in the rope (`01,2625` to `01,2703`) are copied from the listing.
+  - `ERASABLE_ASSIGNMENTS.agc`: "EIGHT SETS OF 12 REGISTERS EACH" (the core sets), five VAC areas.
+  - `PINBALL_NOUN_TABLES.agc`: Noun 63 (absolute velocity, altitude rate, computed altitude), Noun 64 (time left
+    for redesignation and LPD angle, altitude rate, altitude), Noun 68 (slant range to the landing site, time to go in
+    the braking phase, LR altitude minus computed altitude), Noun 60.
+  - `LUNAR_LANDING_GUIDANCE_EQUATIONS.agc`, `THE_LUNAR_LANDING.agc`: V06N63 in P63, V06N64 in P64, DELTAH for V16N68.
+  - `ALARM_AND_ABORT.agc`: BAILOUT1's `INDEX Q` / `CAF 0`, which fetches the alarm code from the rope.
+- **[E1]** Don Eyles, [Tales from the Lunar Module Guidance Computer](https://www.doneyles.com/LM/Tales.html)
+  (AAS, 2004): the duty-cycle margins (over 15 % in braking, about 13 % once the landing radar's data come in, 10 %
+  or less with Verb 16 Noun 68 up, below 10 % in P64), the radar's TLOSS (2 angles × up to 6,400 pulses per second,
+  13 % assumed, 13.36 % measured after the flight), SERVICER every 2 s, 8 core sets and 5 VAC areas, the restart
+  that keeps only the newest SERVICER and drops the uncompleted ones and the Noun 68 monitor, high gate at
+  102:41:32 and 7,400 ft, P66 at 102:43:08.
+- **[J]** [Apollo 11 Lunar Surface Journal](https://apollojournals.org/alsj/a11/a11.landing.html), the landing:
+  the crew's altitude and speed call-outs from 5,000 ft to contact, "Delta-H is minus 2,900", the ALT light out at
+  102:38:11, the altitude and velocity lights near the surface, "Contact light" at 102:45:40.
+- **[R]** Apollo 11 Mission Report and NASA timeline: PDI at 102:33:05, alarms at 102:38:22 (1202), 102:39:02
+  (1202), 102:42:18 (1201), 102:42:43 (1202), 102:42:58 (1202).
+- **[G]** [Apollo descent guidance](https://www.nasa.gov/wp-content/uploads/static/history/alsj/ApolloDescentGuidnce.pdf) (report on the ALSJ):
+  the braking phase ends about 7,800 m in slant range from the landing site.
+- **[D]** The LM DSKY: the photographs at the Computer History Museum and NASM (Wikimedia Commons, below), the
+  Luminary lamp list; 8 × 8 × 7 in.
+- **[H]** The AGC's instruction timing (Virtual AGC, "Assembly language manual"): 12 timing pulses per MCT, AD in
+  2 MCT, TC and TCF in 1, DXCH in 3.
+- **[P]** Pinball (the DSKY program in Luminary): a Verb 16 monitor redisplays once a second.
+- **[Q]** [Quindar tones](https://www.nasa.gov/wp-content/uploads/static/history/alsj/quindar.html), ALSJ:
+  2,525 Hz to key the ground transmitter, 2,475 Hz to release it, 250 ms each.
+- **[A]** Apollo Operations Handbook, Block II spacecraft, vol. 1, section 2.10, caution and warning
+  ([ibiblio](https://www.ibiblio.org/apollo/ApolloProjectOnline/Documents/SMA2A-03-BLOCK%20II%20Volume%201%2019691015/aoh-v1-2-10-c+w.pdf)):
+  the master alarm tone is a square wave alternately 750 and 2,000 Hz. That is the command module's handbook; the
+  score assumes the LM's tone was the same.
+
+## Estimates and simplifications **[E]**
+
+| What | In the model | Why |
+|---|---|---|
+| Job mix of the Executive | SERVICER every 2 s (needs a VAC area), a Verb 16 monitor job every second at lower priority, an LPD display job every 2 s in P64 from 12 s after high gate, one keyboard job per key | the real Luminary job list is longer; this is the smallest mix that shows the mechanism Eyles describes |
+| Priorities | relative only (keyboard > SERVICER > monitor, LPD) | the numbers are not shown on screen; the priority word in the erasable view uses PRIO20 / PRIO10 and an estimated low-9-bit pointer (`0154`) |
+| Radar data load | +1.5 % (ramping over 24 s once the landing radar locks at 102:38:11) | Eyles gives "perhaps 13 %" margin; 1.5 % instead of 2 % keeps the braking phase from drifting into overload between the second alarm and P64, as it did not in flight |
+| P64 duty | 83.5 % rising to 90 % at P66 | Eyles: margin below 10 % in P64; the ramp places the model's P64 alarms near the flown ones |
+| Crew keystrokes | V16 N68 entered at PDI + 305 s, V05 N09 after the first alarm, V16 N68 again at PDI + 350 s, RSETs | the keystroke times are not in the transcript; they are set so the model's first two 1202s land at 317.4 s and 356.4 s after PDI (flown: 317 and 357) |
+| Descent profile before high gate | a smooth braking profile through 50,000 ft at PDI, 33,500 ft at the first alarm, 7,400 ft at high gate; horizontal speed 5,560 ft/s at PDI | nobody called numbers in the braking phase; the call-outs after high gate are the crew's [J] |
+| Delta-H | −2,900 ft when the radar locks [J], then decaying with a 38 s time constant | the shape of its incorporation is not published |
+| Rope strand mapping | word w of a module sits on core w mod 512, strand ⌊w / 512⌋ | the real mapping (address bits to core and strand) is more involved; this one puts consecutive addresses on neighbouring cores, so the 9 cores shown hold the real words `01,2623` to `01,2633` |
+| Phases inside the memory cycle | inhibit, set, reset, strobe drawn over the 12 pulses; the 16 bits drawn one after the other | the sense amplifiers read all 16 at once; the drawing staggers them so the eye can follow |
+| Erasable plane | 34 × 11 cores of one bit plane (bit 14), coincident-current X / Y lines, one sense line | the AGC's erasable module packs 32,768 cores; the plane is a window onto one of them |
+| Inside tray B | the rope bay at one end (3 across, 2 deep), B7-B17 standing across the middle, the X-ribbed plate at the other end | after the photographs of the opened trays; the exact positions are approximate |
+| Model's P64 alarms | three 1201s at 577, 586 and 598 s | flown: a 1201 at 553 s and two 1202s at 578 and 593 s; the model's VAC areas run out before its core sets |
+| The instruction-per-second figure | 85,333 MCT/s; additions take 2 MCT, so 42,667 additions/s | "about 85,000 instructions per second" holds only for one-MCT instructions (TC, TCF) |
+
+## The model, by hand
+
+- 2.048 MHz ÷ 2 = 1.024 MHz; 12 pulses = 11.72 µs per memory cycle; 85,333 cycles a second.
+- 6 modules × 512 cores × 12 words = 36,864 words of rope = 36 banks of 1,024; × 16 bits = 589,824 bits.
+- 2,048 erasable words × 16 bits = 32,768 cores.
+- The radar's two angles at 6,400 pulses per second each steal 12,800 MCT a second: 15.0 % at most; 13 % in the model.
+- At the first alarm: 85 % braking + 1.5 % radar data + 3 % Noun 68 + 13 % stolen = 102.5 % of the machine.
+- CAF NO.CORES at `01,2627` is `32634` octal = `011 010 110 011 100`, eight ones; the parity bit is 1.
+
+`node machines/rope/check.mjs` recomputes each of these from the code, runs the Executive's log and compares its
+alarms with Apollo 11's.
+
+## Study material
+
+The photographs and documents the geometry was built against belong to their authors and are not in this
+repository (they sit in `machines/rope/ref/`, which git ignores):
+
+- Ken Shirriff's photographs in [S]: the AGC closed, the two trays opened, tray B, a rope module opened, the rope
+  diagram.
+- [Apollo DSKY at the Computer History Museum](https://commons.wikimedia.org/wiki/File:Apollo_DSKY_CHM.agr.jpg)
+  (Arnold Reinhold, CC BY-SA), [Apollo Guidance Computer at NASM](https://commons.wikimedia.org/wiki/File:Apollo_Guidance_Computer_(NASM).JPG),
+  [AGC logic module](https://commons.wikimedia.org/wiki/File:AGClogicmodule.agr.jpg),
+  [core rope memory](https://commons.wikimedia.org/wiki/File:Apollo_guidiance_computer_ferrit_core_memory.jpg).
+- The Luminary 099 source files listed in [L].
+
+The console's lettering is Barlow Condensed (SIL Open Font License, [@fontsource/barlow-condensed](https://fontsource.org/fonts/barlow-condensed)).

machines/rope/agc-film/main.js

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+// Rope, the film. Shared code in ../agc-shared.
+import {run} from '../agc-shared/film.js';
+
+run();

machines/rope/agc-film/sfx.json

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+{"keys":[29.224,29.513,29.802,30.162,30.451,30.74,31.173,32.111],"alarms":[{"t":27.6,"code":1202},{"t":33.503,"code":1202},{"t":35.132,"code":1201},{"t":35.189,"code":1201},{"t":35.266,"code":1201}],"calls":[[28.5,29.9],[31.2,32.2],[37.6,38.8]],"quindar":{"intro":2525,"outro":2475,"ms":250}}

machines/rope/agc-film/timeline.json

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+{"duration":40,"beats":{"views":[3,6.8,14.6,20.2,24,32.4],"ropeRead":10.2,"erasRead":16,"alarm":27.6,"ff":32.4,"contact":37.4}}

machines/rope/agc-live/main.js

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+import {runLive} from '../agc-shared/live.js';
+
+// Rope as an interactive page: seven subsystems, sections, views, the DSKY's keys, the radar's cycle steals, the
+// mission speed, orbit and zoom, and an auto tour when left alone.
+runLive();