nrf52840, hang on boot if connected to linux via usb

[viric]

I have a RAK4631 and if I boot meshtastic in it (testing 2.7.3) then I see about 10 lines of log messages when opening the serial port (cat /dev/ttyACM0 or screen /dev/ttyACM0, no difference), and all stops.
Even the LED doesn't beat as usual, and meshtastic CLI doesn't work either (after closing cat/screen).

I would like to debug the boot sequence but this makes reading the log impossible.

Does anybody know what may be causing this?

Example of lines I see:

��@INFO  | ??:??:?? 1 

//\ E S H T /\ S T / C

DEBUG | ??:??:?? 1 Filesystem files:
DEBUG | ??:??:?? 1  adafruit (directory)
DEBUG | ??:??:?? 1  bond_prph (directory)
DEBUG | ??:??:?? 2  bond_cntr (directory)
DEBUG | ??:??:?? 2  prefs (directory)
DEBUG | ??:??:?? 2    channels.proto (102 Bytes)
DEBUG | ??:??:?? 2    module.proto (121 Bytes)
DEBUG | ??:??:?? 2    config.proto (173 Bytes)
DEBUG | ??:??:?? 2    device.proto (121 Bytes)
DEBUG | ??:??:?? 2    nodes.proto (10508 Bytes)
DEBUG | ??:??:?? 2 Power::lipoInit lipo sensor is not ready yet
DEBUG | ??:??:?? 2 Use analog input 5 for battery level
INFO  | ??:??:?? 2 Scan for i2c devices
DEBUG | ??:??:?? 2 Scan for I2C devices on port 1
INFO  | ??:??:?? 2 No I2C devices found
DEBUG | ??:??:?? 2 acc_info = 0
INFO  | ??:??:?? 2 S:B:9,2.7.3.cf574c71d,rak4631,meshtastic/firmware
DEBUG | ??:??:?? 2 Reset reason: 0x0
DEBUG | ??:??:?? 2 Set random seed 164989167
INFO  | ??:??:?? 2 Init NodeDB
INFO  | ??:??:?? 2 Load /prefs/nodes.proto
INFO  | ??:??:?? 2 Loaded /prefs/nodes.proto successfully
INFO  | ??:??:?? 2 Loaded saved nodedatabase version 24, with nodes count: 80
INFO  | ??:??:?? 2 Load /prefs/device.proto
INFO  | ??:??:?? 2 Loaded /prefs/device.proto successfully
INFO  | ??:??:?? 2 Loaded saved devicestate version 24
INFO  | ??:??:?? 2 Load /prefs/config.proto

and here all stops.

Unplugging the node from the USB it works perfectly well. It doesn't matter if I use cat or screen or nothing at all, it always get stuck if connected to the linux pc.

[viric]

Oh on RAK4631 the serial console is disabled by default, unlike the rpi2040. I went further enabling it.

But still, often it hangs after these lines:

INFO  | ??:??:?? 2 [ExternalNotification] Turning off external notification: 
INFO  | ??:??:?? 2 [ExternalNotification] 0 
INFO  | ??:??:?? 2 [ExternalNotification] 1 
INFO  | ??:??:?? 2 [ExternalNotification] 2 
INFO  | ??:??:?? 2 [ExternalNotification]
INFO  | ??:??:?? 2 [RangeTest] Range Test Module - Disabled

But sometimes it boots fine, the immediate next lines being

DEBUG | ??:??:?? 5 [PowerFSM] Init NRF52 Bluetooth
INFO  | ??:??:?? 5 [PowerFSM] Init the Bluefruit nRF52 module

Any idea what may occur in the middle that often hangs on boot, if the serial line is connected to a pc/android?

[viric]

Reducing the PowerFSM boot timeout from 3s to 1s it always boots well.

If I press keys (serial tx) during those 3s boot timeout, it boots fine as well.

[viric]

I couldn't make sense of it after trying to debug the OSThread, the InterruptableDelay etc.

So I changed the PowerFSM boot time from 3 to 2 seconds and now it works fine and I can use the rak4631 from the serial port.