Application note AN12419 for secure JTAG

[spiderman]

I am using i.MX RT1062.

AN12419 is quite unclear.

The beginning of chapter 2 says "The secure JTAG mode is typically enabled
in the factory manufacturing and not used during the development."

If I look into Figure 1, it seems that as soon as the secure JTAG is activated (JTAG_SMODE != 00), the "CM7 DAP" is detached. Therefore it seems that with the secure JTAG the only way to go is using SJC on the lower part of the figure. But SJC says "Test control only".

Therefore I am asking:

What can exactly and in detail be done with secure JTAG enabled?

Can I debug like while developing? What happens if I want to solve a bug on a device that have the JTAG secured? Can I do that with MCUXpresso?

Thank you!

[spiderman]

The only way that I was able to connect through JTAG with a SEGGER J-Link was after blowing the DAP_SJC_SWD_SEL fuse (this was in a board with HAB enabled).

But:

A. I could only connect at speed < 70 kHz. Why?

B. I am not able to do any debugging. If I stop the debugger I see that it is executing within Boot ROM addresses, even if I enable "attach to running target". What to do?

C. "What happens if I want to solve a bug on a device that have the JTAG secured?" You said: "As long as you have the secret key to access va JTAG you can update the bug". Could you be more specific please? Can I set breakpoints and see variable values? This is what I mean for debugging.

Thank you.

[Miguel04]

According to the datasheet the JTAG's frequency operations is between 0.001 - 22 MHz and the frequency depends on the target of the SJC.

You asked what happens if it is secured and you wanted to update a bug, and you can update it "Only the devices authorized for debugging (with the right response) can access the JTAG port, otherwise
JTAG access is denied" AN12419

Yes you can add breakpoints and see the variables using MCUXpresso.

Miguel.

[Miguel04]

Hi @spiderman 

JTAG is mainly used for programming the mcu.

Can I debug like while developing?

- MCUXpresso allows you tu make changes on the code while you have an active debug session, however, you will need to re-flash the mcu with the ne changes.

What happens if I want to solve a bug on a device that have the JTAG secured?

- As long as you have the secret key to access va JTAG you can update the bug.

Can I do that with MCUXpresso?

- Yes, MCUXpresso supports this interface.

Best Regards, Miguel.