ImportError: gpio_deep_sleep_hold on MicroPython 1.29 (ESP32-S3) breaks every import of walter_modem

[bmeares]

Summary

On MicroPython 1.29.0, import walter_modem fails on an ESP32-S3 (Walter) with:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/lib/walter_modem/__init__.py", line 1, in <module>
  File "/lib/walter_modem/modem.py", line 3, in <module>
  File "/lib/walter_modem/core.py", line 6, in <module>
ImportError: can't import name gpio_deep_sleep_hold

core.py imports the symbol at module scope:

from esp32 import gpio_deep_sleep_hold  # core.py:6

so the failure is not confined to deep-sleep users — it takes down every import of the library, and with it any application module that imports it at startup.

Cause

ports/esp32/modesp32.c has guarded this function for several releases:

#if SOC_GPIO_SUPPORT_HOLD_IO_IN_DSLP && !SOC_GPIO_SUPPORT_HOLD_SINGLE_IO_IN_DSLP

The guard is unchanged between v1.28.0 and v1.29.0. What changed is the IDF underneath it: 1.29 builds against ESP-IDF v5.5.2, which sets SOC_GPIO_SUPPORT_HOLD_SINGLE_IO_IN_DSLP for the ESP32-S3. The whole-GPIO-bank hold is therefore compiled out on the S3, leaving only per-IO hold (Pin(..., hold=True) / gpio_hold_en()).

Reproduce

1. Flash ESP32_GENERIC_S3-20260824-v1.29.0.bin to a Walter.
2. Install walter_modem (any version through current main).
3. import walter_modem.

Works on v1.28.0, fails on v1.29.0.

Suggested fix

Guard the import, since ModemCore.__init__ is the only caller:

try:
    from esp32 import gpio_deep_sleep_hold
except ImportError:
    def gpio_deep_sleep_hold(_enable):
        pass

Or, if the intent is to preserve pin state across deep sleep on newer builds, call gpio_hold_en() per pin (via Pin(..., hold=True)) where the bank hold is unavailable — the S3 supports the per-IO form.

Happy to send a PR for the guarded-import version if that's the direction you'd prefer.