Why is serial console acting unreliably on Linux board?

by MMA3   Last Updated April 15, 2019 10:25 AM

I am using DIGI Starter Board with ConnectCore i.MX6UL processor running on Linux and I have problems with serial console. I am not connecting through console connector, but UART pins on Raspberry Pi Expansion connector.

enter image description here

enter image description here

enter image description here I replaced resistor R104 to position R83 and R105 to R84. Just in case I also removed resistors R72 and R73 so console connector is disconnected from ConnectCore.
I also supply the board from expansion connector.

I use FT2232D for converting single USB to dual serial ports. One port is for ConnectCore, second one is for Cisco. The port for Cisco runs without problems every time, but sometimes I have problems with serial for ConnectCore.
At first insert of USB cable after powering the device, the serial port runs without problem.
Then after reconnecting USB cable while the device is on, one of the following happens:

  • Console still runs without problem. After login to console in PuTTY i can see this line enter image description here
  • Console transmits and also receives signals (I can see it on LEDs and also having characters in PuTTY), but it doesn't obay any command (help, reboot...). Line looks just like this
    enter image description here
    Maybe I just somehow need to switch between consoles.
  • I transmit signal from my PC, but I have none received - no characters showing in PuTTY and only Tx LED is blinking. I think that is software problem because I checked with oscilloscope on processor pins that it receives signal but it doesn't transmit.

What troubles me the most is the fact that these states occure randomly.

When I restart the device, serial port runs again.

Can you, please, tell me, what could cause these problems?

Thank you.

EDIT: console schematic below enter image description here

Tags : usb serial linux

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