Snake II

Snake II as the Nokia 3310 plays it, on the phone's own screen. Enter on the palette's row (or its hotkey) opens it as a view level whose body is the extension's own page (surface/, a surface view node): the 84 by 48 pixels of the 3310's LCD, drawn pixel for pixel, with the phone's menus, fonts, sprites, mazes, rules, delays and buzzer.

Nothing here is a remake from memory. Every screen, sprite, maze, rule, delay and tone was read off the real 3310 firmware (version 6.07) running in a DCT3 emulator, and the host tests replay 123 runs recorded from that firmware through this extension, comparing every frame, every tone and every backlight switch (see "How it was measured").

Playing

Opening the view enters Snake II as picking it from the phone's Games menu does: the SNAKE II splash, then its menu (New game, Level, Mazes, Top score, Instructions). The screen is lit green in the menus and unlit in play, as the phone keeps its backlight. The panel's title line, above the phone, keeps the top score in view ("Top score 213"), so it reads without opening the Top score screen.

• Steering: 2 4 6 8 (the arrows while playing) turn up, left, right and down. 1 3 7 9 turn across the way the snake goes (moving right, 1 and 3 turn up, 7 and 9 down); * and # turn left and right, as do the phone's scroll keys (Page Up and Page Down here). A key back the way the snake came is dropped; only the last key before a step counts, one turn per step, and a key in the direction the snake already goes cancels a waiting turn. 5 and 0 do nothing.
• Levels: 1 to 9, a step every 656 ms at level 1 down to 88 ms at level 9 (82, 60, 47, 37, 28, 22, 17, 13, 11 units of 8 ms). Food is worth the level.
• Mazes: No maze (the snake wraps at every edge) and Mazes 1 to 5, each with its own start; the snake wraps wherever a maze leaves an edge open.
• Growing: the head enters the food on one step, the tail holds on the next, and the swallowed food rides down the body as a bulge until the tail passes it.
• Bonus creatures: after every fifth food eaten while none is on screen, one of six creatures comes for 20 steps, its countdown and icon at the top right; eaten, it is worth 5 x level + 5 + 2 x the countdown and the snake does not grow.
• The split-second before a crash: a step into a wall or the body does not happen; the phone tries again about 100 ms later with whatever turn was pressed meanwhile, so a late turn still saves the snake. Reversing the blocked turn in that moment does not.
• Game over: the snake blinks off and on, then "Game over!" with the score; a new top score gets fireworks and the jingle, and "TOP SCORE:".
• Pausing: C or Menu in play opens the menu with Continue first; Continue shows the game still, and the next key goes on. Escape (leaving the view) and the panel hiding pause the same way, and Continue is there when you come back, across restarts. A new level or any maze chosen from that menu ends the paused game, as on the phone.
• Leaving: C on the Snake II menu leaves the game (the phone goes back to its Games list), and so does a digit, * or # on any of its screens: on the phone that starts dialling. Both close the view.

The phone's random numbers are its own: rand() starts from 1 at a power-on and is never reseeded, so the first food after a power-on is always at column 3, row 6, and the food and creatures after it follow the phone's sequence. A power-on here is pal starting: the first time the page asks the extension (the extension host keeps the flag). The numbers carry on across games and across opening and closing the view, as the phone's do between power-ons.

Keyboard

The browser's own key repeat is ignored; a held scroll key repeats as the phone's does (the first repeat after 0.8 s, then every half second).

Setup

Nothing to install and no permission. The phone's memory (the level, the maze, the top score, a paused game, rand()'s state) is in the extension's storage (<data dir>/pal/storage/snake.json).

Settings, [extensions.snake]:

Not the phone

Everything else is the firmware's; these are pal's additions, each marked EXTRA, not the firmware in the code, and none of them runs in the replays:

• Turn queue (queue_turns, on by default). The 3310 keeps one turn per step and judges a key against the way the snake last moved, so moving right, up then left in one step turns up and loses the left (the left reverses "right"); moving left, the left cancels the up. With the queue on, that second key waits and turns on the next step. Keys the firmware keeps behave as on the phone (down then up still turns up).
• Top score in the title line, so it reads without the Top score screen.
• Leaving the panel pauses the game as C does; Continue waits in the menu.
• Leaving Snake II closes the view: C on its menu, or a digit (the phone's dialer), where the phone would show its Games list.
• The keyboard map (arrows for 2 4 6 8, Enter for the soft key, Backspace for C) and cmd+T for the tones.

How it was measured

The reference is the 3310's firmware v6.07 (MAME romset noki3310) in djr-747/nokia-dct3-emulator, driven key by key with every LCD change and buzzer register write logged with its emulated time. From it:

• The pictures: the in-game sprites are the firmware's 4 by 4 cell patterns (lcd.ts); everything else (menu labels, the path's small font, soft keys, the Level screen, the notes and their tick, the Top score screen and its coin cup, the instructions, the game over texts and their large digits, the splash, the fireworks) is cut out of the firmware's own frames (bitmaps.ts, generated) and composed as the phone composes it.
• The rules and delays: game.ts (the snake) and phone.ts (its screens), in the firmware's game unit (8 ms on a real phone, from footage of real 3310s; 7.745 ms in the emulator). The disassembly gave rand() (seed * 0x625F + 0x3623 mod 0xFFF1), the food's and the creature's placement, and the creature table (rand() % 6).
• The proof: host/test/extensions/snake-emulator.fixture.json holds 123 recorded runs (menus and their keys, every level and maze played to the end, bonus creatures eaten and missed, the collision grace at levels 1 and 9, pauses and Continue, deaths with and without a top score, keys during each, held keys). snake.test.ts replays each run's keys through this extension and requires every frame to be identical, pixel for pixel, in order, with the buzzer's tones and the backlight's switches in the same order and time.

What no recording can settle is marked in the code and left as the best reading:

• The LCD's colours (from a photo of a 3310, unlit and lit by its backlight) and the buzzer's loudness (the volume register read as steps of loudness).
• The re-check after a blocked step comes about 12.3 units (98 ms) after it in this model, the keypad scan is 2.3 units (18 ms): those two fit every run recorded at levels 1 and 9, where the emulator's own clock jitters by about one unit.
• A power-on is pal starting.
• A 2 by 2 bonus creature the firmware can draw but was never seen (its trigger is unknown) is not drawn.
• Keys the recordings do not cover act as their nearest recorded kind: C on a still game after Continue carries on like any other key, and a held scroll key does not repeat in play.

Platforms

macOS and Linux, the same on both: everything is in-process.