Hi everyone, Bit of an obscure issue, but very easily replicated. I am running Linaro Ubuntu 12.04 on the UDOO. When attempting to communicate through Linux to the Arduino (using /dev/ttymxc3 serial interface) after a fresh Linux boot, everything works fine. Code: root@udoo:~# stty -F /dev/ttymxc3 speed 9600 baud; line = 0; -brkint -imaxbel root@udoo:~# stty -F /dev/ttymxc3 115200 root@udoo:~# cat /dev/ttymxc3 [TEMP] - Temperature is 43.41 C [SERIAL] - Input char [FAN] - Timer started. Fan will run for 320 seconds, unless temp drops below 30C first [TEMP] - Temperature is 43.18 C [SERIAL] - Input char ^C root@udoo:~# (the serial output from the Arduino is seen after the 'cat' command. Everything is working fine here) I can reset the Arduino (by way of using the RESET pin and some code (as seen in STEP 1, here: http://www.instructables.com/id/two-way ... -software/) and all is still working fine. But then, when I upload the sketch to the Arduino (using USB cable to my PC and J18 disconnected) 'cat' no longer shows any output. It remains this way until I reboot Linux. Then it works again until I upload a sketch to Arduino again. Has anyone else had this same issue? Any way to fix this? Thanks.