BBB UART broken or is this normal behaviour?

I have some strange behaviours on the UART’s of my beaglebone black. I have done the same test (like below) on UART1; UART2 and UART4, and they are all acting the same way.

I did the following test:

  • bridged (loopbacked) the port
  • open two terminal windows
  • on one terminal window I listen the port
  • on the other I send the string olivier

The message sends out quickly, but on the receiving end it takes about 15 seconds before the message appears on the screen. And after that it keeps on appearing, until I stop it with ctrl-c.

If I try to unexport the overlay, it closes my ssh connection and on the second terminal window, kernel errors appear. The BBB freezes now until I reboot it. Could it be that my UART’s are broken or is normal behaviour?

You can't share serial ports between multiple processes, threads or similiar. What happens is that two processes are opening the same port which leads to undefined operations (it likely confuses the kernel).

Alexander Holler