[SOLVED] ARM Cortex M3 How do I determine the program counter value before a hard fault?

ARM Cortex M3 How do I determine the program counter value before a hard fault?

I have an embedded project using a STM32F103 (ARM Cortex M3), it is getting a occasionally getting hard fault in release mode. As part of recovery, I would like to retrieve the PC value from before the hard fault and store it for later debugging in the battery backed region.

How would I determine the value of the program counter at the point of the hard fault? Obviously, the PC is now set to its location within the hardfault interrupt.

Where should I look? It there an address for the normal mode register bank?

Thanks!

Solution

Cortex-M3 uses a quite different model of exception handling from the "classic" ARM, e.g. it doesn't have "abort mode" mentioned in the other post. I suggest you to read this app note. For example, for the Hard Fault:

The value of SCB->BFAR indicates the memory address that caused a Bus Fault and is valid if the bit BFARVALID in the SCB->CFSR register is set. The value of SCB->MMFAR indicates the memory address that caused a Memory Management Fault and is valid if the bit MMFARVALID in the SCB->CFSR register is set.

To determine the PC value at the time of exception you need to examine the stack; the processor pushes R0-R3, R12, PC and LR before executing the handler. The stack used can be either Main (if bit 2 of LR is 0) or Process (otherwise). See page 13 of the app note for details.