embassy-rs/embassy · error

Pin has no IOMUXC definitions

Error message

Pin {} has no IOMUXC definitions

What it means

During build-script codegen for pin peripherals, `generate_iomuxc` filters pins that should have IOMUXC mux definitions and then unwraps the `iomuxc` field of each matched pin. A pin reaching that closure without `iomuxc` data means the chip metadata and the filter are inconsistent — an internal invariant of the generated metadata — so the script panics naming the pin.

Solutions

1. Update embassy-nxp and its metadata dependencies to matching, latest versions (`cargo update -p embassy-nxp`).
2. Verify the enabled chip feature is one officially supported by this embassy-nxp release; try a different/older chip feature.
3. If reproducible on a supported chip, file a bug with the chip name and pin from the panic message — this is a crate-side metadata bug.

Example fix

// Cargo.toml
// before
embassy-nxp = { git = "https://...", features = ["mimxrt1170"] }  # metadata mismatch
// after
embassy-nxp = { version = "0.1", features = ["mimxrt1062"] }     # supported chip, matching metadata

// Build-time panic; guard by pinning known-good versions.
// Cargo.toml
[dependencies]
embassy-nxp = { version = "=0.1.0", features = ["mimxrt1062"] } // exact pin, avoid metadata skew

When it happens

Trigger: Building embassy-nxp against a chip whose metadata contains a pin where the filter accepted it (`iomuxc` with `mux.is_some()`) but `pin.iomuxc` is `None` at the unwrap point — i.e. a metadata/chip-definition inconsistency in the crate, not user input.

Common situations: Using a recently added or poorly supported chip feature where metadata tables are incomplete; mixing embassy-nxp versions where the `imxrt-ral`/metadata crate and embassy-nxp got out of sync; a bug in the crate's chip metadata generator.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Invalid ADC channel side
• no SYSCTL peripheral
• AHB frequency is too low
• No mimxrt/lpc Cargo feature enabled
• Multiple mimxrt/lpc Cargo features enabled

AI-assisted analysis of embassy-rs/embassy@463a07b963 (2026-09-10). Data as JSON: /api/errors/44dfe089dd1640d5. Report an issue: GitHub.

Appendix: source

Thrown at embassy-nxp/build.rs:157

            let channel_number = signal.name.strip_prefix("OUT").unwrap().parse::<u8>().unwrap();
            let name = format!("SCT{instance}_OUT{channel_number}");

            singletons.push(Singleton { name, cfg: None });
        }
    }

    singletons
}

#[cfg(feature = "_rt1xxx")]
fn generate_iomuxc() -> TokenStream {
    let iomuxc_pad_impls = metadata::METADATA
        .pins
        .iter()
        .filter(|p| p.iomuxc.as_ref().filter(|i| i.mux.is_some()).is_some())
        .map(|pin| {
            let Some(ref iomuxc) = pin.iomuxc else {
                panic!("Pin {} has no IOMUXC definitions", pin.name);
            };

            let name = Ident::new(pin.name, Span::call_site());
            let mux = iomuxc.mux.unwrap();
            let pad = iomuxc.pad;

            quote! {
                impl_iomuxc_pad!(#name, #pad, #mux);
            }
        });

    let base_match_arms = metadata::METADATA
        .peripherals
        .iter()
        .filter(|p| p.name.starts_with("GPIO"))
        .map(|peripheral| {
            peripheral.signals.iter().map(|signal| {
                // All GPIO signals have a single pin.

View on GitHub (pinned to 463a07b963)