WatchdogChannels::Channels bitmask is not supported for…

Error message

WatchdogChannels::Channels bitmask is not supported for AWD1; use Single or All

What it means

For ADC4's analog watchdog 1 on this family, the hardware can only watch either one specific channel (AWD1SGL with AWD1CH) or all channels. The embassy API's WatchdogChannels::Channels(bitmask) variant cannot be expressed in AWD1 registers, so setup_awd panics and directs the user to Single or All instead.

Solutions

Use WatchdogChannels::Single(channel) to monitor one specific channel with AWD1
Use WatchdogChannels::All to monitor all enabled channels
Switch the watchdog to AWD2 or AWD3 if your target supports channel-bitmask selection there

Example fix

// before
let cfg = WatchdogConfig::new(WatchdogChannels::Channels(bitmask));
// after
let cfg = WatchdogConfig::new(WatchdogChannels::All); // or WatchdogChannels::Single(channel)

Defensive patterns

Strategy: validation

Validate before calling

match channels {
    WatchdogChannels::Channels(_) => panic!("AWD1 cannot use a channel bitmask; use Single or All"),
    _ => {}
}

Prevention

Remember AWD1 supports only Single or All; reserve bitmask configs for AWD2/AWD3
Read the ADC4 watchdog section of the reference manual before configuring
Centralize watchdog channel config in one helper to keep constraints visible
Check cfg(stm32u5) code paths when porting between families

When it happens

Trigger: Calling `enable_watchdog`/watchdog configuration on ADC4 with `WatchdogChannels::Channels(bitmask)` selected for AWD1.

Common situations: Copying watchdog config that used the bitmask variant from AWD2/AWD3 code (which do support channel groups); assuming AWD1 supports multiple arbitrary channels; upgrading embassy-stm32 where AWD1 gained stricter validation.

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/3570b42adda72a2b. Report an issue: GitHub.

Appendix: source

Thrown at embassy-stm32/src/adc/watchdog_adc4.rs:221

                        w.set_ht3(high_threshold);
                    }
                });

                T::regs().cfgr1().modify(|w| {
                    w.set_awd1en(true);
                    #[cfg(stm32wba)]
                    {
                        use crate::pac::adc::vals::Awd1sgl;
                        match channels {
                            WatchdogChannels::Single(ch) => {
                                w.set_awd1sgl(Awd1sgl::SingleChannel);
                                w.set_awd1ch(ch);
                            }
                            WatchdogChannels::All => {
                                w.set_awd1sgl(Awd1sgl::AllChannels);
                            }
                            WatchdogChannels::Channels(_) => {
                                panic!(
                                    "WatchdogChannels::Channels bitmask is not supported for AWD1; use Single or All"
                                );
                            }
                        }
                    }
                    #[cfg(stm32u5)]
                    {
                        match channels {
                            WatchdogChannels::Single(ch) => {
                                w.set_awd1sgl(true);
                                w.set_awd1ch(ch);
                            }
                            WatchdogChannels::All => {
                                w.set_awd1sgl(false);
                            }
                            WatchdogChannels::Channels(_) => {
                                panic!(
                                    "WatchdogChannels::Channels bitmask is not supported for AWD1; use Single or All"

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