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led2d

device_envoy::led2d

Macro led2d 

Source 
macro_rules! led2d {
    ($($tt:tt)*) => { ... };
}
Available on non-crate feature host only.
Expand description

Macro to generate an LED-panel struct type (includes syntax details). See Led2dGenerated for a sample of a generated type.

See the led2d module for usage examples.

Syntax:

led2d! {
    [<visibility>] <Name> {
        pin: <pin_ident>,
        led_layout: <LedLayout_expr>,
        font: <Led2dFont_expr>,
        pio: <pio_ident>,               // optional
        dma: <dma_ident>,               // optional
        max_current: <Current_expr>,    // optional
        gamma: <Gamma_expr>,            // optional
        max_frames: <usize_expr>,       // optional
    }
}

§Fields

Required fields:

  • pin — GPIO pin for LED data
  • led_layout — LED strip physical layout (see LedLayout); this defines the panel size
  • font — Built-in font variant (see Led2dFont), e.g. Led2dFont::Font4x6Trim. Bring Led2dFont into scope or use a full path like device_envoy::led2d::Led2dFont::Font4x6Trim.

The led_layout value must be a const so its dimensions can be derived at compile time.

Optional fields:

  • pio — PIO resource to use (default: PIO0)
  • dma — DMA channel (default: DMA_CH0)
  • max_current — Electrical current budget (default: 250 mA)
  • gamma — Color curve (default: Gamma::Srgb)
  • max_frames — Maximum number of animation frames for the generated strip (default: 16 frames)

max_frames = 0 disables animation and allocates no frame storage; write_frame() is still supported.

§Current Limiting

The max_current field automatically scales brightness to stay within your electrical current budget.

Each WS2812 LED is assumed to draw 60 mA at full brightness. For example:

  • 16 LEDs × 60 mA = 960 mA at full brightness
  • With max_current: Current::Milliamps(1000), all LEDs fit at 100% brightness
  • With the default electrical current limit (250 mA), the generated MAX_BRIGHTNESS limits LEDs to ~26% brightness

The electrical current limit is compiled into a lookup table at device initialization, so it has no per-frame runtime cost.

Powering LEDs from the Pico’s pin 40 (VBUS): Pin 40 is the USB 5 V rail pass-through, but the Pico itself has practical electrical current limits — the USB connector, cable, and internal circuitry aren’t designed for heavy loads. Small LED panels (a few hundred mA) can usually power from pin 40 with a decent USB supply; for larger loads (1 A+), use a separate 5 V supply and share ground with the Pico.

§Color Correction (Gamma)

The gamma field applies a color response curve to make colors look more natural:

The gamma curve is compiled into a lookup table at device initialization, so it has no per-frame runtime cost.

  • led_strips! — Alternative macro to share a PIO resource with other panels or LED strips (includes examples)
  • led_strip! — For 1-dimensional LED strips