Arty A7 35T + MicroBlaze: On-board UART interface causes processor to halt

[DerekM]

Hi, I have a strange problem when trying to communicate with the MicroBlaze processor on an Arty A7. Basically, Uart communications is fine when using Tera Term for basic printf messages when the application is downloaded to the board. However, as soon as another application is used to open the connection to the Com port (with Tera Term disconnected, obviously), the processor halts or possibly goes into a reset state.

The issue does not occur when I use the Pmod USB-Uart to do the exact same thing (i.e. view messages using Tera Term on start-up, and then communicate with a command handler on the platform using LabVIEW).

Is there a known issue with the on-board USB-UART (FTDI) path on the Arty A7?

Some pictures which should help to show the issue:

 

[DerekM]

Okay, worked it out. Quite simple in the end (if somewhat annoying): When jumper JP2 is fitted, the MicroBlaze is being reset when Python/LabVIEW/etc access the COM port. The issue goes away when the jumper is removed. So it's a feature, not a bug ?. (A statement I've used many times in the past.)