After playing around with different U-Boot versions, It naturally happend that my GuruPlug did not work any more at all. This means that the serial output did not show anything at all, because the U-Boot was messed up. Nice guides like this (link to the GuruPlug installer) or this show how easy it is to just flash the U-Boot again, using the JTAG-module. However, it was not that easy at all.

After doing a lot of research, all I found was that it is very tricky to get the timing right between powering up/resetting the GuruPlug and starting the flashing. Threads like this one show such suggestions. However, in my cause the timing or JTAG-speed had nothing to do with my flashing problems, the only problem was the hardware with some loose connections.

I only discovered the hardware-problems "by accident". I opened my GuruPlug to see if there is any hint on how to do some hardware modifications which would help with the reset and flash timing. Since I still had in my mind that somewhere I read about someone having hardware/connection problems, I started pulling/pushing/turning on the JTAG-connection a little while the GuruPlug installer was running. Suddenly, the flashing did not stop with the previous errors any more. I then had to find the right position of my GuruPlug board and the JTAG-module and I was able to repeat the flashing, as long as the devices were in the right position.

 

In this thread, I described the errors which appeared when the flashing did not work. In the process of trying to find the right position for my GuruPlug and JTAG-module, I created a script which repeatedly starts the GuruPlug installer script runme.sh. Just save the following code in a file called run.sh, and start it with "sudo ./run.sh"

#!/bin/bash

for i in {1..1000};
do
   output=$(sudo sh ./runme.sh ./openocd/uboot.bin)

   if [[ "$output" =~ "openocd FAILED" ]]
   then
     echo ">>> not successful"
     echo " "
     echo " "
     sleep 1
   else
     echo ">>> done <<<"
     echo " "
     echo " "
     break
fi

done

 

Some more info can be found in this thread.