Struct Vblank 

pub struct Vblank(/* private fields */);

The frame clock: proof that the VBlank interrupt is reaching the counter.

Everything that waits for a frame hangs without it.

Implementations

impl Vblank

pub unsafe fn listen() -> Self

Listen for the VBlank interrupt.

Safety

Turns interrupts on. That is preemption, which the surrounding code may have been written to rule out.

pub fn frame_count(&self) -> u8

Frames counted since boot, wrapping at 256.

wrapping_sub of two readings is the frames between them; a plain subtraction is what overflows across the wrap.

pub fn wait(&self)

Block until the next frame.

The CPU sleeps while waiting. Does not return with the LCD off, since no VBlank arrives then, nor where a replacement handler skips frame_tick.

pub fn with<R>(&self, f: impl FnOnce(Access<'_>) -> R) -> R

Wait for the next frame, then run f inside its VBlank.

Nothing enforces the window. f keeps running once the PPU has moved on, and writes past that point are dropped in silence.

vblank.with(|d| {
    bg::set_scroll(d, camera_x, camera_y);
    obj::set(d, 0, player);
});

// Overruns: the tail of the tileset lands after the window and is lost.
// `with_lcd_off` has no deadline.
vblank.with(|d| load_tileset(&TILES, d));

Waiting goes through wait, so this does not return under the same conditions.

Trait Implementations

impl !Send for Vblank

impl !Sync for Vblank