Struct FamilyKeyboardState 

pub struct FamilyKeyboardState { /* private fields */ }

The Famicom Family BASIC keyboard overlay state.

Per the NESdev “Family BASIC Keyboard” page, the keyboard is a 9 x 8 switch matrix (with the data-recorder lines unused here) read through the expansion port but software-visible on $4017. The protocol:

• $4016 write — bit 0 (the “column” select; 0 selects the low 4 keys of the current row, 1 selects the high 4) and bit 1 (a clock; a 0->1 transition advances to the next row). Bit 2 enables the keyboard matrix; when bit 2 is 0 the matrix is disabled and $4017 reads 1s. Writing bit 1 = 0 while bit 2 = 1 resets the row counter to 0.
• $4017 read — bits 4..1 carry the four key switches of the currently selected (row, column-half), active-low (0 = pressed). There are 9 rows x 2 halves = 18 selectable groups of 4 keys = 72 key positions.

We model the live pressed state as a 72-bit key bitmap ([u8; 9], one byte per row: low nibble = column-half 0, high nibble = column-half 1) and the row counter + column select per the write protocol. Determinism holds: it is a pure function of the writes + the live key bitmap.

Implementations

impl FamilyKeyboardState

pub const fn new() -> Self

New keyboard with no keys held, matrix reset + disabled.

pub const fn set_keys(&mut self, keys: [u8; 9])

Set the full pressed-key bitmap (one byte per matrix row; low nibble = column-half 0, high nibble = column-half 1). The frontend builds this from host keys via its key map.

pub const fn set_key(&mut self, index: usize, pressed: bool)

Set one key by linear index (0..72) — index = row * 8 + bit, matching the matrix layout (bit 0..=3 = column-half 0, 4..=7 = column-half 1). Out-of-range indices are ignored.

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

Handle a $4016 write: latch column select (bit 0), advance the row on a clock (bit 1) rising edge, set the matrix-enable (bit 2). A clock low while enabled resets the row counter to 0.

pub const fn read(&self) -> u8

Read the device byte for a $4017 access. The four selected key switches are returned on bits 4..1, active-low (0 = pressed). When the matrix is disabled, all four bits read 1 (no keys). The caller ORs in the open-bus upper bits.

pub const fn peek(&self) -> u8

Side-effect-free sample of the device byte (debugger peek) — identical to Self::read (the keyboard read has no side effects).

pub const fn from_parts( keys: [u8; 9], row: u8, column: bool, enabled: bool, clock: bool, ) -> Self

Reconstruct from save-state parts.

pub const fn keys_raw(&self) -> [u8; 9]

Raw per-row key bitmap (save-state).

pub const fn row_raw(&self) -> u8

Raw row counter (save-state).

pub const fn column_raw(&self) -> bool

Raw column select (save-state).

pub const fn enabled_raw(&self) -> bool

Raw matrix-enable (save-state).

pub const fn clock_raw(&self) -> bool

Raw clock level (save-state).

Trait Implementations

impl Clone for FamilyKeyboardState

fn clone(&self) -> FamilyKeyboardState

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for FamilyKeyboardState

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

Formats the value using the given formatter.

impl Default for FamilyKeyboardState

fn default() -> Self

Returns the “default value” for a type.

impl Copy for FamilyKeyboardState