USB UART Open Causes Power Cycle Under Certain Conditions

Technical Support
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1

Environment

Verdin iMX8MP Q 4GB WB IT V1.0B
Dahlia V1.1A
19V/3.42A Barrel Jack Power
Native HDMI Out to Monitor
Debug USB-C to USB Host
DRP USB-C to USB Host
(Ubuntu 20.04 Host)

Summary

Under certain conditions, opening a UART connection to the USB debug port will cause the board to power down and go into an unrecoverable state.

Steps to Reproduce

Note: This is not the only scenario where this has been observed, but it is the easiest to reproduce

  1. Plug in the cables mentioned in the environment setup
  2. Boot to recovery mode
  3. Load Tezi
  4. On host, open a UART connection to DEBUG port on carrier board e.g screen /dev/ttyUSB0
2

Verdin debug UART is working in a terminal mode. Please use a minicom or any other terminal instead of screen.

3

Screen is capable of working in serial terminal mode when used as described above, it is functionally equivalent to minicom.

Also my question is not how to use a UART terminal, but why the board is power cycling when a signal is sent on a UART port.

4

Could you specify a TEZI version? I can’t replicate this issue on my set up using Tera term.

5

Verdin-iMX8MP_ToradexEasyInstaller_5.3.0+build.3 is the TEZI version.

To confirm, you were using the same exact hardware revisions as listed above above?
Verdin iMX8MP Q 4GB WB IT V1.0B
Dahlia V1.1A

6

Since Verdin iMX8M plus software is in a beta stage we recommend to use a latest nightly build as it stated here. However I’ve tested 5.3.0 version and it has no issue with debug serial port as well.

Are you sure you are opening the debug port but not the FDTI JTAG or FTDI GPIO (power/reset control) ? When you plug your dev machine to Dahlia X18 connector you will have 4 COM ports on your dev machine. The last one is a debug. Please refer to Dahlia board schematic for details.