Implementation is limited to

Error message

Implementation is limited to {} unique sample times among all channels.

What it means

The v3 (F3/G0-style) ADC implementation caches at most SAMPLE_TIMES_CAPACITY distinct sample-time values because each SMPR register can hold a limited table of unique sample times (SMPSEL indirection). If a sequence introduces more distinct sample times than the capacity, the driver panics — this is a limitation of the driver's modeling, not of the hardware itself.

Solutions

Reduce the number of distinct SampleTime values — use one common sample time for all channels in the sequence
Split the sequence into multiple configure_sequence calls grouped by sample time
Adjust channel sampling needs so channels share sample times where accuracy permits

Example fix

// before
let pts = [SampleTime::Cycles1_5, SampleTime::Cycles7_5, SampleTime::Cycles13_5, SampleTime::Cycles28_5, ...]; // > capacity distinct values
// after
let pts = [SampleTime::Cycles239_5; N]; // single shared sample time

Defensive patterns

Strategy: validation

Validate before calling

let unique: std::collections::HashSet<_> = sample_times.iter().collect();
assert!(unique.len() <= SAMPLE_TIMES_CAPACITY, "too many distinct ADC sample times");

Prevention

Use a single SampleTime for all channels in a sequence unless accuracy demands otherwise
Group channels by sample time into separate sequences
Check SAMPLE_TIMES_CAPACITY in adc/v3.rs before designing long mixed sequences
Review sample times when porting examples from other families

When it happens

Trigger: Calling `configure_sequence` (e.g. via `sample_sequence`) with channels whose requested SampleTime values span more unique values than SAMPLE_TIMES_CAPACITY across all channels in one sequence.

Common situations: Configuring a long sequence where each channel got a slightly different sample time copy-pasted from examples; mixing 1.5/7.5/239.5-cycle times across many channels; upgrading embassy and hitting a newly added capacity limit.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of embassy-rs/embassy@463a07b963 (2026-09-10). Data as JSON: /api/errors/bfa4149e61d5449e. Report an issue: GitHub.

Appendix: source

Thrown at embassy-stm32/src/adc/v3.rs:324

            let mut last_channel: u8 = 0;

            self.chselr_1().write(|w| {
                for (i, ((channel, _), sample_time)) in sequence.enumerate() {
                    // Determine if we can use sequencer
                    needs_hw = needs_hw || channel > CHSELR_SQ_MAX_CHANNEL;
                    is_ordered_up = is_ordered_up && (channel > last_channel || i == 0);
                    is_ordered_down = is_ordered_down && (channel < last_channel || i == 0);
                    hw_channel_selection |= 1 << channel;
                    last_channel = channel;

                    // Assign & check sample times
                    self.smpr().write(|smpr| {
                        if let Some(j) = sample_times.iter().position(|&t| t == sample_time) {
                            smpr.set_smpsel(channel.into(), (j as u8).into());
                        } else {
                            smpr.set_sample_time(sample_times.len(), sample_time);
                            if let Err(_) = sample_times.push(sample_time) {
                                panic!(
                                    "Implementation is limited to {} unique sample times among all channels.",
                                    SAMPLE_TIMES_CAPACITY
                                );
                            }
                        }
                    });

                    // Prepare sequencer
                    if !needs_hw {
                        w.set_sq(i, channel.into());
                    }
                }

                // Terminate sequence
                for i in sequence_len..CHSELR_SQ_SIZE {
                    w.set_sq(i, Sq::Eos);
                }
            });

View on GitHub (pinned to 463a07b963)