XIAO nRF52840 + Wio-SX1262: MeshCore stops working after power cycle, no BLE advertising and no response over USB

[pawelglogowski]

Board / hardware

• Seeed Studio XIAO nRF52840 + Wio-SX1262 kit
• Product link: https://botland.com.pl/loralorawan/26528-zestaw-xiao-nrf52840-wio-sx1262-do-meshtastic-lorabluetooth-seeedstudio-102010710-5904422387815.html

Problem summary
MeshCore worked correctly on this board for about 2 days.
After disconnecting power and reconnecting it, the device stopped working correctly:

• BLE Companion no longer advertises
• other devices/phones cannot see it over Bluetooth
• USB port still appears when connected to a computer
• MeshCore firmware does not respond correctly over USB either

Important detail
This does NOT look like a dead board:

• the UF2 bootloader still works
• the USB serial port appears on macOS
• if I flash Meshtastic back onto the same board, Bluetooth works and the phone can connect
  This strongly suggests the hardware is OK and the problem is MeshCore-specific.

What happened

1. The board was bought with factory Meshtastic firmware.
2. I flashed MeshCore onto it.
3. MeshCore worked normally for around 2 days.
4. After unplugging power and plugging it back in, the blue LED stopped blinking and BLE stopped advertising.
5. Since then, I have not been able to recover MeshCore functionality.

What I tested
I tested all of the following:

1. Official MeshCore flasher

• Performed erase using the official MeshCore flasher
• Reflashed using the official MeshCore flasher
• Tested multiple firmware roles:
  • BLE Companion
  • USB Serial Companion
  • Repeater
  • Room Server
• Tested multiple versions down to v1.10.0
• Also tried builds from the build page, including dev branch and a custom repeater build with MESH_DEBUG enabled

2. BLE Companion

• After flashing BLE Companion, the device is not visible over Bluetooth
• Other devices do not see it
• No connection possible

3. USB Serial Companion

• USB serial port appears on macOS, e.g. /dev/cu.usbmodem101
• meshcli can open the port
• But the node does not answer the companion protocol handshake

Command used:
meshcli -D -s /dev/cu.usbmodem101

Output:
DEBUG:meshcore:port opened
INFO:meshcore:Serial Connection started
DEBUG:meshcore:Connected successfully: /dev/cu.usbmodem101
DEBUG:meshcore:Sending appstart command
DEBUG:meshcore:Sending raw data: bytearray(b'\x01\x03 mccli')
DEBUG:meshcore:sending pkt : b'<\r\x00\x01\x03 mccli'
DEBUG:meshcore:Dispatching event: EventType.CONNECTED, {'connection_info': '/dev/cu.usbmodem101'}, {}
ERROR:meshcore:No response from meshcore node, disconnecting
ERROR:meshcore:Are you sure your node is a serial companion ?
ERROR:meshcore:To connect to a repeater, use -r option.

4. Repeater

• I flashed repeater firmware

• config.meshcore.dev times out while connecting

• It shows:
  "Cannot connect: Command timeout: time 1773679798"

• meshcli in repeater mode opens the serial port but still gets no response to commands like ver

Command used:
meshcli -D -r -s /dev/cu.usbmodem101 ver

Output:
INFO:meshcore:Connecting to repeater at /dev/cu.usbmodem101 (115200 baud)...
DEBUG:meshcore:Serial port opened: Serial<id=0x106c41ff0, open=True>(port='/dev/cu.usbmodem101', baudrate=115200, bytesize=8, parity='N', stopbits=1, timeout=1, xonxoff=False, rtscts=False, dsrdtr=False)
INFO:meshcore:Disconnected from repeater.

In interactive mode, typing ver or other commands also produces no response.

5. Custom debug build

• I built xiao_nrf52_repeater from the build page
• Enabled Debug logging (MESH_DEBUG)
• Result was the same: port opens, but no useful response from firmware

6. Manual UF2 flashing

• The UF2 bootloader volume appears normally
• I can enter bootloader mode
• But MeshCore images still do not start/respond correctly after flashing

Control test: Meshtastic
If I flash Meshtastic UF2 onto the same exact board:

• Bluetooth works
• the phone can discover and connect to the device

This is the strongest indication that:

• board is not dead
• BLE hardware is not dead
• USB is not dead
• the problem is likely MeshCore on this target, possibly triggered by power-cycle/reboot

Expected behavior
After power cycling the board, MeshCore should boot normally and:

• BLE Companion should advertise again, or
• USB Serial Companion should answer the companion protocol, or
• Repeater should answer serial CLI commands

Actual behavior
After power cycle:

• BLE Companion does not advertise
• USB Serial Companion does not respond
• Repeater serial CLI does not respond
• config.meshcore.dev times out
• only the USB port itself still enumerates

Question
Could this be a boot/startup issue specific to the xiao_nrf52 target (or xiao_nrf52_repeater / companion_radio_usb / BLE companion variants), possibly triggered by power loss / reboot?

[pawelglogowski]

I found a workaround and likely narrowed this down to boot/startup code on xiao_nrf52, not a hardware fault.

What I changed
I tested disabling two startup paths that looked suspicious on xiao_nrf52.

1. RTC autodiscovery in:

• variants/xiao_nrf52/target.cpp

Original:

bool radio_init() {
    rtc_clock.begin(Wire);
    return radio.std_init(&SPI);
}

Changed to:

bool radio_init() {
    return radio.std_init(&SPI);
}

Result:

• this improved things significantly
• BLE advertising came back
• the phone could see and connect to the device again
• however, after connecting, the app still failed with:
  • "Failed to fetch device info"
  • timeout

2. Environment sensor startup in: examples/companion_radio/main.cpp

I commented out:

sensors.begin();
sensors.loop();

Result:

• after rebuilding Xiao_nrf52_companion_radio_ble with both changes above, the firmware started working correctly
• BLE advertising works
• phone connects
• device info is fetched correctly
• MeshCore now works again on this board

Conclusion
There appear to be at least two startup-time problems on xiao_nrf52:

• rtc_clock.begin(Wire) / RTC autodetection can block or destabilize boot
• EnvironmentSensorManager startup (sensors.begin() and/or sensors.loop()) can also block or break normal Companion initialization

In my case:

• removing only RTC autodetection restored BLE advertising/connection
• removing sensor startup as well fixed the remaining "Failed to fetch device info" timeout

So this looks like a target-specific boot/init issue on xiao_nrf52, not a dead board.