ESP32‑P4 + ESP32‑C5（WT01P4C5‑S1）WiFi init fails with RuntimeError: Wifi Unknown Error 0xffffffff

[hatsuneIridium]

Hi everyone,
I’m using the Wireless‑Tag WT01P4C5‑S1 board, which has ESP32‑P4 (host) and ESP32‑C5 (WiFi/BLE co‑processor) on board, connected via SDIO.
Board info: https://www.wireless-tag.com/product-item-101.html
You can download the document for the Wireless-Tag WT01P4C5-S1 board from the board info.

My setup

P4 firmware:
Official MicroPython GENERIC_ESP32P4 with Support for external C5 WiFi/BLE (v1.28.0, 2026‑04‑06).
Repo:https://micropython.org/download/ESP32_GENERIC_P4/
C5 firmware:
Built from espressif/esp‑hosted‑mcu (latest main branch, no code changes) for ESP32‑C5, flashed as the slave co‑processor firmware.
Repo: https://github.com/espressif/esp-hosted-mcu
Transport: SDIO (on‑board wiring as per manufacturer schematic).
ESP‑IDF version for building C5 fw: 5.5.4(as required by esp‑hosted‑mcu).

Minimal test code (REPL)

import network
wlan = network.WLAN(network.STA_IF)
wlan.active(True)  # <-- crashes here

Error

MPY: soft reboot
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
RuntimeError: Wifi Unknown Error 0xffffffff

The error happens immediately at wlan.active(True), before any connect or scan.
What I’ve checked
Both chips flash successfully; basic GPIOs/UART work.
C5 runs the esp‑hosted‑mcu slave firmware (no obvious boot errors on serial).
P4 MicroPython is the correct “external C5” variant.
This is not a “flash C5 with MicroPython” mistake — C5 is running the Espressif co‑processor firmware.

My question / ask for help

Are there any specific sdkconfig / menuconfig options I must set when building esp‑hosted‑mcu for ESP32‑C5 as SDIO slave to work with MicroPython’s external WiFi driver?
Does MicroPython’s network module for “external C5” require a specific version or branch of esp‑hosted‑mcu?
Are there known issues with ESP32‑P4 + C5 over SDIO in current MicroPython / esp‑hosted‑mcu?
I also opened an issue yesterday with the same problem:#19217
Any guidance on correct C5 firmware build config, required pins, or debug steps would be greatly appreciated.
Thanks!