What causes "Multiple time-driver-xxx Cargo features enabled" in embassy-rs/embassy?

Keep exactly one `time_driver_*` feature (or none, for the default) in your embassy-mspm0 dependency.

Multiple time-driver-xxx Cargo features enabled

Error message

Multiple time-driver-xxx Cargo features enabled

What it means

embassy-mspm0 supports several time-driver timer choices exposed as `time_driver_<timer>` Cargo features (e.g. time_driver_tima0). The build script's `time_driver` function uses `get_one` to require at most one such feature; when two or more are enabled it panics with this message, failing the build.

Solutions

Keep exactly one `time_driver_*` feature (or none, for the default) in your embassy-mspm0 dependency.
Remove the redundant feature: `cargo tree -f '{p} {f}' -i embassy-mspm0` reveals where the extra feature comes from.
If a dependency enables a time driver, use its chosen driver rather than enabling a conflicting one.

Example fix

// before
features = ["time_driver_tima0", "time_driver_timg0"]
// after
features = ["time_driver_tima0"]

Defensive patterns

Strategy: validation

Validate before calling

// At most one time_driver_* feature:
// features = ["mspm0g350x", "time_driver_tima0"]

Prevention

When switching time drivers, remove the old feature in the same commit.
Check `cargo tree -f '{p} {f}' -i embassy-mspm0` when a dependency also uses embassy-mspm0.
Omit time_driver features entirely unless you need a non-default timer.

When it happens

Trigger: Enabling two time-driver features simultaneously, e.g. `features = ["time_driver_tima0", "time_driver_timg0"]`, or having a dependency enable a different time-driver feature that Cargo unifies with yours.

Common situations: Merging two projects' dependency blocks; a BSP crate enabling its own time driver feature; switching drivers by adding the new feature but forgetting to remove the old one.

Understand the failure class

Background: "mutually exclusive" flag errors: what "can't supply both nx and xx", "--raw is not compatible with -i" and "cannot be used with" mean, and how to fix them — this error's family across 29 libraries.

Related errors

AI-assisted analysis of embassy-rs/embassy@463a07b963 (2026-09-10). Data as JSON: /api/errors/e14c46da8390e0eb. Report an issue: GitHub.

Appendix: source

Thrown at embassy-mspm0/build.rs:429

fn time_driver(singletons: &mut Vec<Singleton>, cfgs: &mut CfgSet) {
    // Timer features
    for (timer, _) in TIMERS.iter() {
        let name = timer.to_lowercase();
        cfgs.declare(&format!("time_driver_{}", name));
    }

    let time_driver = match env::vars()
        .map(|(a, _)| a)
        .filter(|x| x.starts_with("CARGO_FEATURE_TIME_DRIVER_"))
        .get_one()
    {
        Ok(x) => Some(
            x.strip_prefix("CARGO_FEATURE_TIME_DRIVER_")
                .unwrap()
                .to_ascii_lowercase(),
        ),
        Err(GetOneError::None) => None,
        Err(GetOneError::Multiple) => panic!("Multiple time-driver-xxx Cargo features enabled"),
    };

    // Verify the selected timer is available
    let selected_timer = match time_driver.as_ref().map(|x| x.as_ref()) {
        None => "",
        // TODO: Fix TIMB0
        // Some("timb0") => "TIMB0",
        Some("timg0") => "TIMG0",
        Some("timg1") => "TIMG1",
        Some("timg2") => "TIMG2",
        Some("timg3") => "TIMG3",
        Some("timg4") => "TIMG4",
        Some("timg5") => "TIMG5",
        Some("timg6") => "TIMG6",
        Some("timg7") => "TIMG7",
        Some("timg8") => "TIMG8",
        Some("timg9") => "TIMG9",
        Some("timg10") => "TIMG10",

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