does not support use as a time driver on this chip yet…

Error message

{time_driver_singleton} does not support use as a time driver on this chip yet: N6's LPTIM register layout (split isr_output/dier_output/icr_output registers) and RCC clock-mux selection are not yet implemented for the time driver. Select a TIM-based time driver (e.g. time-driver-any) instead.

What it means

The build script rejects LPTIM as a time driver on STM32N6 because the N6 LPTIM register layout (split isr_output/dier_output/icr_output registers) and its RCC clock-mux selection are not implemented in embassy-stm32's time driver. Selecting an LPTIM time-driver feature on an N6 target deliberately panics in build.rs instead of generating broken code.

Solutions

Use `time-driver-any` or an explicit TIM-based feature (e.g. `time-driver-tim2`) so a regular timer is selected.
If LPTIM is required, file/watch an upstream embassy issue for N6 LPTIM time-driver support rather than patching features.
As a workaround, patch embassy-stm32 to add N6 LPTIM support in the time driver (register layout + RCC mux).

Example fix

# before
features = ["stm32n657xx", "time-driver-lptim1"]
# after
features = ["stm32n657xx", "time-driver-any"]

Defensive patterns

Strategy: validation

Validate before calling

// Don't select LPTIM as time driver on STM32N6:
// features = ["stm32n657xx", "time-driver-any"]

Prevention

On N6, always use TIM-based or `time-driver-any` features.
Read the target chip's supported-feature notes before choosing time-driver features.
Watch upstream embassy release notes for N6 LPTIM time-driver support.

When it happens

Trigger: Building for an STM32N6 target with a time-driver feature that resolves to an LPTIM instance (regs.kind == "lptim" && regs.version == "n6"), e.g. `time-driver-lptim1` instead of a TIM-based driver.

Common situations: Users of STM32N6 who assumed LPTIM works like on other families; copying configs from other chips; trying low-power timers specifically for stop-mode timekeeping.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of embassy-rs/embassy@463a07b963 (2026-09-10). Data as JSON: /api/errors/2991def1d5cf7a3a. Report an issue: GitHub.

Appendix: source

Thrown at embassy-stm32/build.rs:413

    let time_driver_irq_decl = if !time_driver_singleton.is_empty() {
        cfgs.set(format!("time_driver_{}", time_driver_singleton.to_lowercase()), true);

        let Some((p, regs)) = peripheral_map.get(time_driver_singleton.as_str()) else {
            panic!("Tried to select {time_driver_singleton}, which is not available on this device");
        };

        // Tell the time driver how wide the timer's counter is.
        if regs.kind == "timer" {
            cfgs.enable(if regs.block == "TIM_GP32" {
                "time_driver_32bit"
            } else {
                "time_driver_16bit"
            });
        }

        if regs.kind == "lptim" && regs.version == "n6" {
            panic!(
                "{time_driver_singleton} does not support use as a time driver on this chip yet: N6's LPTIM \
                 register layout (split isr_output/dier_output/icr_output registers) and RCC clock-mux \
                 selection are not yet implemented for the time driver. Select a TIM-based time driver \
                 (e.g. time-driver-any) instead."
            );
        }
        let irqs: BTreeSet<_> = p
            .interrupts
            .iter()
            .filter(|i| i.signal == "CC" || i.signal == "UP" || i.signal == "GLOBAL")
            .map(|i| i.interrupt.to_ascii_uppercase())
            .collect();

        irqs.iter()
            .map(|i| {
                let irq = format_ident!("{}", i);
                quote! {
                    #[cfg(feature = "rt")]

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