What causes "Selected output pixel format not supported" in embassy-rs/embassy?

Set the output format to one of Argb8888, Rgb888, Rgb565, Argb1555, Argb4444.

Selected output pixel format not supported

Error message

Selected output pixel format not supported

What it means

The Into<vals::OpfccrCm> conversion maps the typed PixelFormat enum to the DMA2D output-color-model register bits; the wildcard arm was reached with a variant (such as a YCbCr format, only accepted by background/foreground layers on dma2d_v2 hardware) that the output layer cannot express, so the conversion panics rather than produce a wrong register value.

Solutions

Set the output format to one of Argb8888, Rgb888, Rgb565, Argb1555, Argb4444.
Use a different PixelFormat for the output layer than restricted input formats.

Example fix

// before
let out = OutputLayer::new(&mut dma2d, buf, layout, PixelFormat::A4);
// after
let out = OutputLayer::new(&mut dma2d, buf, layout, PixelFormat::Argb8888);

Defensive patterns

Strategy: validation

Validate before calling

fn assert_output_format(f: PixelFormat) {
    assert!(matches!(f, PixelFormat::Argb8888 | PixelFormat::Rgb888 | PixelFormat::Rgb565 | PixelFormat::Argb1555 | PixelFormat::Argb4444),
        "format not supported as DMA2D output");
}

Type guard

fn is_output_pixel_format(f: PixelFormat) -> bool { matches!(f, PixelFormat::Argb8888 | PixelFormat::Rgb888 | PixelFormat::Rgb565 | PixelFormat::Argb1555 | PixelFormat::Argb4444) }

Prevention

Use only the five output-capable formats for the destination layer.
Assert output format validity at display-init time.

When it happens

Trigger: Setting the DMA2D output/framebuffer pixel format with L4, A8, A4, AL44, AL88, or a YCbCr variant via the Into<OpfccrCm> conversion during display configuration.

Common situations: Reusing an input-layer pixel format constant for the output layer; misreading docs where L8/L4/A8 are legal as inputs but not outputs.

Related errors

AI-assisted analysis of embassy-rs/embassy@463a07b963 (2026-09-10). Data as JSON: /api/errors/920211b4a74abf33. Report an issue: GitHub.

Appendix: source

Thrown at embassy-stm32/src/dma2d/mod.rs:226

            PixelFormat::AL88 => vals::BgpfccrCm::Al88,
            PixelFormat::L4 => vals::BgpfccrCm::L4,
            PixelFormat::A8 => vals::BgpfccrCm::A8,
            PixelFormat::A4 => vals::BgpfccrCm::A4,
            #[cfg(dma2d_v2)]
            _ => panic!("YCbCr pixel format not supported for background buffer"),
        }
    }
}

impl Into<vals::OpfccrCm> for PixelFormat {
    fn into(self) -> vals::OpfccrCm {
        match self {
            PixelFormat::Argb8888 => vals::OpfccrCm::Argb8888,
            PixelFormat::Rgb888 => vals::OpfccrCm::Rgb888,
            PixelFormat::Rgb565 => vals::OpfccrCm::Rgb565,
            PixelFormat::Argb1555 => vals::OpfccrCm::Argb1555,
            PixelFormat::Argb4444 => vals::OpfccrCm::Argb4444,
            _ => panic!("Selected output pixel format not supported"),
        }
    }
}

/// Input buffer alpha Mode
#[derive(Clone, Copy)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub enum AlphaMode {
    /// Do not modify alpha
    NoModify,
    /// Replace alpha
    Replace(u8),
    /// Multiply alpha
    Multiply(u8),
}

impl Into<vals::FgpfccrAm> for AlphaMode {
    fn into(self) -> vals::FgpfccrAm {

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