TX2 dev kit loses HDMI display when UART is connected

We are connecting our TX2 to a dji matrice 100 through UART. Everything runs fine until the UART connection is made which then locks up the TX2 and we lose the display. We have to unplug the UART and reboot to get the TX2 back up and running. Even when we shutdown the the TX2, plug in the UART to the Matrice, boot up, it still has no display output.

The UART is connected through the J21 pins 8,9,10. What could be causing the TX2 to completely lock up when the UART is connected? Could it be that the matrice is trying to send data when the TX2 is not ready for it?

Hi mophead1_1,

Does the system still work? Could you fetch out the dmesg when display is gone?

Did you first disable serial console in both Linux and U-Boot? J21 is serial console, and detecting a keystroke at boot will halt boot.

The system seems to be locked up, I am not sure if we can fetch dmesg when nothing is responding. Originally the M100 was using 240300 baud rate and it was crashing the system every time either on bootup or when the UART was plugged in which would cause the display to shutoff. I did notice that when we plugged in while the system was up and running at this baud rate, we would get a lag on the mouse and keyboard before everything locked up.

When we dropped the baud rate down to 115200 the TX2 was able to boot up with display as long as the M100 was off or the UART was disconnected.

If the M100 is on at 115200, there is no display on bootup. This could be a different issue, one that linuxdev was talking about below.

Although we are not doing any keystrokes at bootup unless the M100 is sending keystrokes.

Almost any traffic at all will cause U-Boot to halt. Even initializing the line to a 1 or 0 will halt boot. If possible do the testing with the M100 disconnected until after the Jetson is already booted. Expect odd behavior or corruption if connected after booted and if the port for serial console has not been disabled for that purpose.