Hi,
This is the first time I post a message on this forum but I have been here may times and have to say that it is an invaluable resource when in trouble. Most likely somebody else has run into the same problems before but that is not the case now.
Here is the situation:
Two custom boards we designed using TM4C1231H6PZI microcontroller and used for several months to develop the firmware without a glitch have failed in the same way within a few hours while attempting a firmware update: microcontrollers fail to boot and can no longer be accessed, either thru JTAG or SWD interface.
While I am not ruling out the possibility that we did something wrong I cannot seem to figure out what has happened. As a side note, new boards were programmed with the same fw update and nothing happened to them.
Assuming it might have been accidentally locked, I have tried unlocking it from LM Flash Programmer with no success.
Further hardware investigation revealed that the JTAG/TDO line is toggling (for the record, at ~13Hz ) as it is mentioned in the datasheet at page 204:
Note: If the device fails the initialization phase, it toggles the TDO output pin as an indication the
device is not executing. This feature is provided for debug purposes.
I have run out of ideas and could not find anything related to this problem on this forum after a few hours of searching.
Before anybody questions it, all hardware is OK, I have replaced the chip on one of them and all hardware is working just fine.
Any ideas? Thank you, Daniel