Tab5: Wi-Fi stops until reboot under memory pressure - ESP-Hosted RX stall (esp-hosted-mcu #243); factory C6 firmware 1.4.1 misses the upstream fix #20

Summary. On a Tab5, one failed internal-DMA allocation in ESP-Hosted's SDIO receive path stops the ESP32-P4 hearing the ESP32-C6 until a reboot. WiFi.status() stays WL_CONNECTED, every request fails (hostByName(): DNS Failed ... error '-54') and nothing is logged. It hits apps that use a lot of internal RAM; here, a 3D view. One of our units sat in this state for four hours.

The root cause is Espressif's open issue esp-hosted-mcu #243. We reproduced it on demand on a stock Tab5 and confirmed it never recovers on its own, even after the memory is freed: details in our comment there.

Why Tab5 owners stay exposed. ESP-Hosted 2.13.1 (22 Oct) fixes this by pre-allocating its receive buffers, but only when the C6 reports ESP_PRIV_TX_Q_SIZE at start-up. The Tab5's factory C6 firmware (ESP-Hosted slave 1.4.1) does not send it over SDIO; generate_startup_event() in its sdio_slave_api.c sends only FIRMWARE_CHIP_ID, CAPABILITY, TEST_RAW_TP and RX_Q_SIZE. So even once Arduino-ESP32 ships 2.13.1, a Tab5 keeps the failing path.

Requests

1. A C6 firmware update for Tab5 owners to ESP-Hosted slave 2.13.1 or later, for example through M5Burner.
2. A note for Tab5 developers about this stall and the workaround below.
3. Optionally, a C6 power-cycle helper in M5Unified (WLAN_PWR_EN, IO expander 0x44 pin P0). Cutting the C6's power for 500 ms and restarting is the reliable way to recover a stuck link today.

A workaround that works now, with Arduino-ESP32's prebuilt libraries: one file and one linker flag (-Wl,--wrap=heap_caps_aligned_alloc). When ESP-Hosted's SDIO tasks cannot get internal DMA memory, they get DMA-capable PSRAM instead: ESP-Hosted's own PREFER_SPIRAM path, in reverse order. With it, the same reproduction no longer stalls: three runs with 42 MB bursts, no RPC timeouts, every TLS request answered. File (MIT): https://github.com/craigdianesmith-glitch/tab5-adsb-flight-tracker-cpp/blob/c9db0de3d3502e94fe863319dd111862fc8f2577/src/hosted_rx_rescue.c. Our app also carries a watchdog as a safety net (src/wifi_watch.cpp in the same repository).

Environment: Tab5 (ESP32-P4 eco2 + ESP32-C6), Arduino-ESP32 3.3.12 (ESP-IDF 5.5.5), ESP-Hosted host 2.12.13, C6 slave 1.4.1 (factory), SDIO 4-bit at 40 MHz, streaming mode.