Module input_device

Expand description

Optional non-standard input-device overlays for the $4016/$4017 controller ports: the Arkanoid “Vaus” paddle and the NES Zapper light gun.

These are opt-in overlays. The bus holds an Option<InputDevice> per port; when a port has no overlay device (the default) the standard controller / Four Score serial path runs completely unchanged, so the default + Four Score reads stay byte-identical and the determinism contract is preserved. A device is only consulted when explicitly attached via crate::Nes::set_paddle / crate::Nes::set_zapper.

§Vaus paddle (Arkanoid controller)

Per the NESdev “Arkanoid controller” page (NES 7-pin version), the device reports on the player-2 port ($4017):

7  bit  0
---- ----
xxxD Bxxx
   | |
   | +---- Fire button (1: pressed)        -> bit 3
   +------ Serial control knob data        -> bit 4
           (8/9-bit, inverted, MSb first)

A write of $4016 bit 0 = 1 -> 0 (the standard controller strobe) starts a “conversion”: the 8-bit potentiometer value is latched MSb-first into the shift register. Each $4017 read shifts out the next bit (on bit 4), inverted on the wire. After the register empties, reads repeat the serial-in bit (the 9th / LSb). The fire button (bit 3) is returned directly and is unaffected by the strobe.

The in-tree vaus-test ROM (Damian Yerrick) documents the NES wiring as $4017 D3: Button, $4017 D4: Position (8 bits, MSB first) — matching the wiki layout above.

§Zapper light gun

Per the NESdev “Zapper” page (NES variant), the device reports on its port:

7  bit  0
---- ----
xxxT Wxxx
   | |
   | +---- Light sensed (0: detected; 1: NOT detected)  -> bit 3
   +------ Trigger (1: pulled/half-pulled; 0: released)  -> bit 4

Note the inverted light polarity: bit 3 is 0 while light is detected and 1 otherwise. The light sensor stays active for roughly 19-26 scanlines after seeing a bright pixel (the photodiode capacitor drains exponentially); we use a simpler frame-granular model: a luminance threshold sampled at the aim point once per completed frame (sufficient because games re-sample every frame). The Zapper has no shift register — its byte is read in parallel and is independent of the strobe.

Structs§

BandaiHyperShotState: The Bandai Hyper Shot (Exciting Boxing punching bag) overlay state (v1.3.0 Workstream F1).
FamilyKeyboardState: The Famicom Family BASIC keyboard overlay state.
KonamiHyperShotState: The Konami Hyper Shot overlay state (v1.3.0 Workstream F1).
PowerPadState: The NES Power Pad (a.k.a. Family Fun Fitness / Family Trainer mat) overlay.
SnesMouseState: The (Hyperkin / Nintendo) mouse overlay state — the SNES-style serial mouse as wired to an NES $4016/$4017 port (D0 serial-out).
VausState: The Arkanoid “Vaus” paddle overlay state.
ZapperState: The NES Zapper light-gun overlay state.

Enums§

InputDevice: An optional non-standard device overlaid on a controller port. When set, the bus’s $4016/$4017 read path returns this device’s byte instead of the standard controller / Four Score serial byte.

Constants§

FAMILY_KEYBOARD_KEYS: Number of physical keys on the Famicom Family BASIC keyboard matrix (9 rows x 8 columns / 2 halves; 72 keys, with a handful of unused matrix positions reported as 1 / not-pressed).