Problems debugging iMXRT1011 project

[expertsleepers]

I have a simple custom board based on an iMXRT1011 processor. I'm using MCUXpresso IDE v24.12 and a Segger J-Link Ultra+. I'm experienced with iMXRT development in general and the J-Link has worked fine for me on another project.

Everything started fine, but at some point, I lost the ability to debug my project. The code runs fine if I install it using the serial boot loader (via the Secure Provisioning tool), but if I flash it from the debugger it doesn't run.

It seems to crash somewhere before main(). Sometimes I can set a breakpoint in ResetISR() and step through. In these cases everything is fine if I keep single stepping, but it crashes if I let it run. Sometimes it goes straight to 0xdeadbeee and there's nothing to debugger can do.

As you can imagine this is very frustrating. Any suggestions would be gratefully received.

[expertsleepers]

If I flash the application with SEC, it runs fine. If I connect with J-Link commander, I can halt and go successfully.

In the IDE, today I can set a breakpoint at ResetISR(). If I step over SystemInit(), it crashes. If I step into SystemInit(), step through the function and then step over SystemInitHook(), it crashes. If I do the same and step into SystemInitHook(), it does not crash. This is what I mean when I say the behaviour depends on whether the debugger is stepping over or into the code.

An example of the stack when it crashes:

Thread #1 57005 (Suspended : Signal : SIGTRAP:Trace/breakpoint trap)

_vfprintf_r() at 0x600134a4

0x0

So it looks like it's jumping to 0x0, but only when the code is freely running, not when stepping in the debugger. There is no code at 0x0 - the ITC is not being used.

Just to repeat, this is before main(), long before any RTOS or similar is invoked. It's crashing in the initial startup code.