PDMIn Bug on ESP32-S2 (NotImplementedError: PDMIn)

[CrackXT]

CircuitPython version and board name

Adafruit CircuitPython 9.2.2 on 2025-01-09; FeatherS2 with ESP32S2
Adafruit CircuitPython 9.2.9 on 2025-09-07; FeatherS2 with ESP32S2
Adafruit CircuitPython 10.1.4 on 2026-03-09; FeatherS2 with ESP32S2
Adafruit CircuitPython 10.2.1 on 2026-05-13; FeatherS2 with ESP32S2
Adafruit CircuitPython 10.3.0-alpha.2 on 2026-05-15; FeatherS2 with ESP32S2

Code/REPL

### Testcode from https://learn.adafruit.com/adafruit-pdm-microphone-breakout/circuitpython with Error -> NotImplementedError: PDMIn

# SPDX-FileCopyrightText: 2018 Kattni Rembor for Adafruit Industries
#
# SPDX-License-Identifier: MIT

import time
import array
import math
import board
import audiobusio


# Remove DC bias before computing RMS.
def mean(values):
    return sum(values) / len(values)


def normalized_rms(values):
    minbuf = int(mean(values))
    samples_sum = sum(
        float(sample - minbuf) * (sample - minbuf)
        for sample in values
    )

    return math.sqrt(samples_sum / len(values))


# Main program
mic = audiobusio.PDMIn(board.D1, board.D12, sample_rate=16000, bit_depth=16)
samples = array.array('H', [0] * 160)


while True:
    mic.record(samples, len(samples))
    magnitude = normalized_rms(samples)
    print((magnitude,))
    time.sleep(0.1)

Behavior

Zurückverfolgung (jüngste Aufforderung zuletzt):
Datei "", Zeile 28, in
NotImplementedError: PDMIn

Description

I encountered an unexpected problem during a project involving a PDM microphone.

According to the changelog, PDMIn has been implemented and available for Espressif MCUs since CP 9.2.2. I could not find any exceptions regarding specific Espressif MCUs; however, there appears to be no support for the ESP32-S2.

The error does not occur with an ESP32-S3.

I modified the code (Where's my PDMIn?) from https://learn.adafruit.com/adafruit-pdm-microphone-breakout/circuitpython to indicate the lack of support. The original code example implies that PDMIn is supported because it lists all pin combinations despite the error.

If it is a hardware limitation, this should be clearly indicated on the page https://learn.adafruit.com/adafruit-pdm-microphone-breakout/circuitpython perhaps my extended code could be published there as an additional "safety measure."

If it is not a hardware limitation, please fix it if possible—thanks.

Additional information

### mod. Testcode (Where's my PDMIn?)

import board
import audiobusio
from microcontroller import Pin


def is_hardware_PDM(clock, data):
    try:
        p = audiobusio.PDMIn(clock, data)
        p.deinit()
        return True
    except ValueError:
        return False
    except RuntimeError:
        raise


def get_unique_pins():
    exclude = ['NEOPIXEL', 'APA102_MOSI', 'APA102_SCK']
    pins = [pin for pin in [
        getattr(board, p) for p in dir(board) if p not in exclude]
            if isinstance(pin, Pin)]
    unique = []
    for p in pins:
        if p not in unique:
            unique.append(p)
    return unique


try:
    for clock_pin in get_unique_pins():
        for data_pin in get_unique_pins():
            if clock_pin is data_pin:
                continue
            if is_hardware_PDM(clock_pin, data_pin):
                print("Clock pin:", clock_pin, "\t Data pin:", data_pin)
except RuntimeError:
    print("PDMIn is not supported on this MCU.")

[dhalbert]

The ESP32-S2 does not support PDM-to-PCM input. See https://docs.espressif.com/projects/esp-idf/en/latest/esp32s2/api-reference/peripherals/i2s.html#overview-of-all-modes. However, it looks like it could be enabled for some other chip types that don't currently have it turned on. So we'll document the ESP32-S2 limitation and check on the other chips.

[CrackXT]

Thanks for the quick feedback. It appears, then, that currently only the ESP32, ESP32-S3, and ESP32-P4 are PDMIn compatible.

Conversely, according to the documentation, the Espressif MCUs supported in CircuitPython do not offer support for PDM-to-PCM conversion:

ESP32-C2 Technical Reference Manual Version 1.3
ESP32-C3 Technical Reference Manual Version 1.4
ESP32-C6 Reference Manual Version 1.2.
ESP32-C61 Technical Reference Manual Version 1.0
ESP32-H2 Technical Reference Manual Version 1.1

I think it would be a good idea to update the page https://learn.adafruit.com/adafruit-pdm-microphone-breakout/circuitpython with this information and list the supported MCUs. Additionally, the "Where's my PDMIn?" demo code could potentially be expanded to include the modification I described above. This would make it immediately apparent to us users that a hardware limitation is involved.

Thank you for your work and to the Adafruit team!

[dhalbert]

I think it would be a good idea to update the page https://learn.adafruit.com/adafruit-pdm-microphone-breakout/circuitpython with this information and list the supported MCUs.

Agree, I've done this.

Additionally, the "Where's my PDMIn?" demo code could potentially be expanded to include the modification I described above. This would make it immediately apparent to us users that a hardware limitation is involved.

This already raises NotImplementedError, as you noted. For example:

Adafruit CircuitPython 10.2.1 on 2026-05-13; Adafruit QT Py ESP32S2 with ESP32S2
>>> import board
>>> import audiobusio
>>> p = audiobusio.PDMIn(board.A0, board.A1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NotImplementedError: PDMIn

Would you want the example to catch that? My impression is that the exception does say why it doesn't work.

[CrackXT]

I agree with you regarding the code example. Yes, the example code in the "Learn Guide"—which catches or ignores the NotImplementedError and allows the code to finish executing—should also be updated.

This applies even though we have now expanded the information on the page.

Here is the output from the current "Where's my PDMIn?" code on the page when running on an ESP32-S2; it lists all pin combinations.

To a beginner, this likely seems contradictory and confusing. Why are pin combinations being shown if my MCU ultimately isn't compatible? Therefore, in my view, it would be a good idea to make the second code example unambiguous for beginners.

I have provided a possible modified version of the code under "Additional information."

Thank you for your work and to the Adafruit team!

[dhalbert]

Ah, I misunderstood the problem. I think the "Where's my PDM?" code could not catch RuntimeError at all, and should be:

def is_hardware_PDM(clock, data):
    try:
        p = audiobusio.PDMIn(clock, data)
        p.deinit()
        return True
    except ValueError:
        return False

This is essentially what you did, but a bit simpler. I can't think of why catching RuntimeError should be considered OK. I tested this on an ESP32-S2, which fails immediately with NotImplementedError, and on and ESP32-S3, which lists a lot of pins, as expected.