MKL16 SWD reset functionality

[mnie]

Hello,

I have a question regarding a Freescale MKL16Z256XXX4 that I am using in a design and firmware update. I have disabled the Reset functionality on the SWD port. By reading the document AN4835 “Production Flash Programming Best Practices for Kinetis K- and L-series MCUs” in section 4.1.1 it says that to establish SWD connection the Reset pin needs to be asserted and then communication can be established with the ARM DAP to update and read MDM-AP for status. The reference manual KL16P80M48SF4RM says in section 9 says that a reset state can be achieved by accessing the DP CTRL/STAT register. The question is, am I always guaranteed to enter a reset state of the MCU by sending commands to the ARM DAP without having the Reset pin available or is the Reset pin mandatory to guarantee prober reset and then firmware download into the MCU? What is the delay from the Reset state is requested by sending data to the MDM-AP to the MCU enters its reset state and is halted and further actions can be performed, i.e. flash erase, programming etc.?

Kind regards, Mads Nielsen

[jorge_a_vazquez]

Hi Mads Nielsen

When you said that you disabled the Reset functionality on the SWD port , do you mean in the Flash Memory module (FTFA_FOPT)?

Yes, You are always guaranteed to enter a reset state of the MCU by sending commands to the ARM DAP without having the Reset pin available, because this commands doesn't use the pin to force a system reset. I made some tests in my side and I successfully could access the DP CTRL/STAT register and request a reset state with the Reset pin disable.

Hope this information helps
Have a great day,
Jorge Alcala