WatchdogChannels::All is not supported for AWD2; use…

Error message

WatchdogChannels::All is not supported for AWD2; use Channels(0x3FFF) to monitor all 14 channels

What it means

The AWD2 analog watchdog on non-U5 ADC4-family STM32 parts has a channel mask register that cannot express 'all channels' as a single value, so the library refuses WatchdogChannels::All instead of silently monitoring nothing. The developer must pass an explicit Channels bitmask covering the 14 channels (0x3FFF). This is a deliberate fail-fast design decision in embassy-stm32's watchdog setup (setup_awd).

Solutions

Replace WatchdogChannels::All with WatchdogChannels::Channels(0x3FFF) to explicitly monitor all 14 channels
If fewer channels are actually needed, pass a narrower mask (e.g. Channels(0x0001) for channel 0) to reduce false watchdog trips
Use AWD1 instead of AWD2 if the watchdog must support an 'all channels' mode on this chip family

Example fix

// before
let config = WatchdogConfig { channel: WatchdogChannels::All, .. };
// after
let config = WatchdogConfig { channel: WatchdogChannels::Channels(0x3FFF), .. };

Defensive patterns

Strategy: validation

Validate before calling

// Rust: const ALL_14: WatchdogChannels = WatchdogChannels::Channels(0x3FFF);
// Only pass WatchdogChannels::All to AWD1; for AWD2/AWD3 always use Channels(mask).

Prevention

Never use WatchdogChannels::All for AWD2/AWD3 on ADC4-family parts
Centralize watchdog channel constants (0x3FFF / 0xFFFFFF) in one module
Add a compile-time or unit-test check that mapping of watchdog -> channels excludes All

When it happens

Trigger: Calling the ADC watchdog API for AWD2 on an ADC4-family (non-stm32u5) chip with WatchdogChannels::All as the monitored-channel configuration, e.g. WatchdogConfig channels field set to WatchdogChannels::All.

Common situations: Porting code written for classic bxCAN-era ADC watchdogs where an 'all channels' variant existed; copying an AWD1 configuration to AWD2; enabling a watchdog on all channels by analogy with other HALs.

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/80d39f062687e99a. Report an issue: GitHub.

Appendix: source

Thrown at embassy-stm32/src/adc/watchdog_adc4.rs:284

                // CFGR1 fields; setting any bit enables monitoring of that channel.
                T::regs().awd2cr().modify(|w| {
                    // Clear all channel bits first, then set the requested ones.
                    #[cfg(stm32wba)]
                    {
                        for n in 0..14usize {
                            w.set_awd2ch(n, false);
                        }
                        match channels {
                            WatchdogChannels::Single(ch) => w.set_awd2ch(ch as usize, true),
                            WatchdogChannels::Channels(mask) => {
                                for n in 0..14usize {
                                    if mask & (1 << n) != 0 {
                                        w.set_awd2ch(n, true);
                                    }
                                }
                            }
                            WatchdogChannels::All => {
                                panic!("WatchdogChannels::All is not supported for AWD2; use Channels(0x3FFF) to monitor all 14 channels");
                            }
                        }
                    }
                    #[cfg(stm32u5)]
                    {
                        for n in 0..24usize {
                            w.set_awdch(n, false);
                        }
                        match channels {
                            WatchdogChannels::Single(ch) => w.set_awdch(ch as usize, true),
                            WatchdogChannels::Channels(mask) => {
                                for n in 0..24usize {
                                    if mask & (1 << n) != 0 {
                                        w.set_awdch(n, true);
                                    }
                                }
                            }
                            WatchdogChannels::All => {

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