I'm experiencing a very, very strange behavior when running debug sessions in STM32CubeIDE. Sequential sessions alternate between correct execution of my main() entry point (and execution stops there, as expected) and unexpected entry into the bootloader.
Everything has worked absolutely correctly up until just a few days ago. Before that, I last compiled and programmed firmware maybe a week and a half ago. I made a git branch at that point to capture the state of the software prior to making changes for a new PCB revision. Now, after experiencing this issue with new code, I've even switched back to that historical branch, and that now also exhibits the issue. I've also rebooted and power cycled my programmer and boards. I have two PCBs, and they both behave the same way.
I'm using STM32CubeIDE v. 1.19.0 build 25607_20250703_0907.
Target is an STM32L431CC (CCT6). Program/debug is via an ST-LINK/V2 and SWD. Nothing has changed in my debug configuration (and reset behavior is "connect under reset", and I have the "set breakpoint at" checkbox checked, with the symbol "main").
On the board, BOOT0 (pin 44) is tied to GND with 10 KΩ.
Nothing has changed with the hardware or the software. And I made the historical branch after having programmed and tested the software. I also verified that in the "failure" case, my reset handler is in fact not being called - a breakpoint at the first instruction of the handler gets hit every other session.
This is the typical sequence I see:
1) I perform a clean and a build to verify compilation (debug configuration, not release).
2) I start a debug session (nothing gets rebuilt). In the debug console, I see everything as expected, up to the message, "Download verified successfully". However, execution does not halt in main(), and the code is running. If I then suspend execution, I'll see an address like 0x1fff2cdc. That's bootloader territory!
3) I terminate and relaunch (nothing gets rebuilt). I see everything as expected, but this time execution halts just inside of main(), as it's supposed to.
4) Behavior in subsequent relaunches alternates between (2) and (3).
This one has me flummoxed. I've found nothing in the forums or elsewhere online that's similar.
Has anyone else experienced anything remotely similar?? (And many thanks in advance to anyone taking the time to share some ideas.)
