Struct PowerPadState 

pub struct PowerPadState { /* private fields */ }

The NES Power Pad (a.k.a. Family Fun Fitness / Family Trainer mat) overlay.

A 12-button mat read on the player-2 port ($4017) through two 8-bit parallel-in/serial-out shift registers (a pair of 4021s), strobed by the standard $4016 controller strobe. The 12 buttons are indexed 0..=11 (matching the mat’s “1”..“12” labels); the frontend decides which physical keys map to which mat button (and any Side-A/Side-B row inversion).

Per the NESdev “Power Pad” page (and Mesen’s implementation), the button bits load into two registers and shift out LSb-first on bits 3 and 4 of each $4017 read:

• register L (bit 3 of the read): buttons 2, 1, 5, 9, 6, 10, 11, 7;
• register H (bit 4 of the read): buttons 4, 3, 12, 8, then four 1 bits.

(Button numbers are 1-based here, matching the mat labels; the code uses 0-based indices.) Each read shifts both registers right and feeds 1s in from the top, so post-shift reads settle to “no button”.

Implementations

impl PowerPadState

pub const fn new() -> Self

New mat with no buttons pressed.

pub const fn set(&mut self, buttons: u16)

Update the live pressed-button mask (bit i = mat button i+1). While the strobe is held high the registers track the live mask (parallel load), matching the standard controller’s latch-while-strobed semantics.

pub const fn write_strobe(&mut self, value: u8)

Handle a $4016 strobe write. While bit 0 is high the registers are (re)loaded from the live buttons; the falling edge leaves the latched snapshot to shift out.

pub const fn read(&mut self) -> u8

Read the device byte for a $4017 access, shifting both registers. Bit 4 = the current serial-out (LSb) of register H, bit 3 = register L; each read then shifts both right (feeding 1s in from the top). The caller ORs in the open-bus upper bits. While the strobe is high the registers are continuously reloaded (reads return the first button).

pub const fn peek(&self) -> u8

Side-effect-free sample of the next device byte (debugger peek).

pub const fn from_parts( buttons: u16, shift_l: u8, shift_h: u8, strobe: bool, ) -> Self

Reconstruct from save-state parts. buttons is masked to the 12 mat bits, matching Self::set, so a malformed save-state cannot inject out-of-range bits.

pub const fn buttons_raw(&self) -> u16

Raw live button mask (save-state).

pub const fn shift_l_raw(&self) -> u8

Raw low shift register (save-state).

pub const fn shift_h_raw(&self) -> u8

Raw high shift register (save-state).

pub const fn strobe_raw(&self) -> bool

Raw strobe state (save-state).

Trait Implementations

impl Clone for PowerPadState

fn clone(&self) -> PowerPadState

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for PowerPadState

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for PowerPadState

fn default() -> PowerPadState

Returns the “default value” for a type.

impl Copy for PowerPadState