carousel

Time-driven page cycler for small displays.

A Carousel answers one question: given the current millisecond clock and whether an external trigger fired, should the display show its idle screen or one of the cycle pages, and which page?

It is pure scheduling. No rendering, no I/O, no atomics, no timer ownership. The caller owns the framebuffer, the clock source, the trigger, and the CarouselState; this crate only maps (now, triggered) to a Frame. That keeps the timing logic no_std, allocation-free, and unit-testable without hardware.

Example

use carousel::{Carousel, CarouselState, Frame};

const SCREENS: Carousel = Carousel {
    page_count: 4,
    page_duration_ms: 5_000,
    cycle_window_ms: 60_000,
    cycle_period_ms: 5 * 60_000, // 0 => trigger-only, never auto-start
};

// Offset the first auto-cycle so the idle screen shows right after boot.
let mut state = CarouselState::new(SCREENS.cycle_period_ms);

// Each render tick, feed the clock and any pending trigger:
match SCREENS.frame_at(&mut state, now_ms, button_pressed) {
    Frame::Idle => { /* draw the idle screen */ }
    Frame::Page(index) => { /* draw page `index` */ }
}

Behaviour

• An automatic burst opens every cycle_period_ms and runs for cycle_window_ms, advancing one page every page_duration_ms and wrapping through 0..page_count. Outside a burst the carousel reports Frame::Idle.
• Passing triggered = true opens a burst immediately without disturbing the automatic schedule, so a manual burst never delays or skips the next periodic one.
• cycle_period_ms = 0 disables automatic bursts: the carousel then cycles only when triggered.
• page_count = 0 reports Frame::Idle on every tick.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE)
• MIT license (LICENSE-MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.