Problems booting board with MK21FN1M0VMC12 (K21 family)

[manjulaellepola]

Hi Community,

We built some proto boards based around the above device. When we got the boards we were able to program and run the device without a problem. Then we added some wires to the board (about 10cm) long to connect one of the I2C ports to a different board. The connections are SCL, SDA, OP line and GND. After we added the wires  the engineer switched on the board and it didn't boot. This was done prior to connecting to the other board. That is the wires were hanging freely. Then we tried to connect the debugger and still no luck. The debugger cannot connect and load the program.

We then did the same on a second identical board. That is the second board also could be programmed and booted as the first. Then we added the wires and the same thing happened as the first. It seems as if some protection on the chip has been activated when it was booted after the wires were added. This device has got tamper protection and other security mechanisms. Could it be that the free hanging wires induced some voltage that the chip thought was a tamper and locked down the chip? Another possibility is that some of the free hanging wires got shorted, could this have damaged the chip or activated the security?

I am interested to see if anyone else has come across something like this and what to do to solve this.

Thanks for your help.

Manjula

[manjulaellepola]

Can a support engineer please try to help me out to get an answer or point me in the right direction? The project is on critical time line and if we don't get support soon we will have to dump this device and move to another solution as the chip is too unstable and I have never come across something like this in my 25+ years of electronic engineering :smileysad:

I can send send schematics if that would help

Thanks in anticipation

Manjula

[Carlos_Mendoza]

Hi Manjula,

Could you share your schematics so I can review them and see if I can find anything that could be causing the behavior you mention?

Thanks in advance!

Best Regards,

Carlos Mendoza

Technical Support Engineer

[manjulaellepola]

Hi Carlos

Thank you very much for responding. I have attached the schematics. We are suspecting some security feature connected with tamper detect kicked in and locked down the chip when the board was booted with the hanging wires. That is the chip saw noise voltage on the input pins of the I2C port and thought it was an attack or something? The I2C port is set up as a slave so SDA and SCL are inputs. Could you please look into the tamper side of things to see if this could have caused it?

We took all anti-static precautions when handling the electronics. Further we didn't enable or disable the security features on the chip intentionally. They would have been in the default state. Basically once the boards arrived we programmed both of them and they worked. Then we added the wires as above and they stopped working after they were powered up. That is the board does not boot or we cannot debug. When we connect the debugger we get a message saying that the Flash is secure and whether to erase. We say erase after that the debugger just stops with an error message. We are using KDS and Multilinx debugger.

We don't have details on the tamper detect system as we need to sign NDA (in process).

Your help to solve this is greatly appreciated.

Best regards

Manjula

[Carlos_Mendoza]

Hi Manjula,

After reviewing the schematics the only thing I would recommend is to place a 0.1 µF capacitor to GND in the JTAG_RST pin. I don't think the tamper pins could have secured the device nor the I2C pins. Have you tried creating a new project and flashing it to the MCU? Is it possible that you send me the project that was first flashed to the board?

About how to recover the secured MCU, please try enabling the "Mass erase on connect" option on the debug configurations:

If the MCU does not get unsecured you could use the P&E Recovery Utility, please take a look to the following post:

Bricking and Recovering FRDM-KL25Z Boards: Reset, SWD Clock and Low Power | MCU on Eclipse

Let me know if it helps!

Best Regards,

Carlos Mendoza

Technical Support Engineer