Display call stack below IRQ handler on MSP430 with IAR

Question

I'm trying to find a stack overflow in a project on MSP430, and found that it occurs mainly when an IRQ occurs after the stack is pretty full.

I've set a breakpoint on a stack pointer write with a value that is smaller than the start address of the stack, and the CPU halts in the IRQ handler.

The call stack display in IAR C-SPY then terminates at the handler function, however I'd be interested in what is below this, as this is what filled the stack.

Is there a way to display the call stack below the current interrupt handler?

Answer 1

If the interrupt handler is written in C, this should work correctly, as the generated CFI (call frame information) should be correct even for interrupt functions.

However, if this (for some reason) should not work, or if the interrupt routine is written in assembler (without proper CFI directives), you can use a little trick. You can manually modify the PC and SP registers in the register window by retrieving the PC from the stack and by "backing up" the SP the amount that it was adjusted inside the function. After this, the debugger will display the function that was executing when the interrupt occurred.

Note, in the traditional MSP430 core, the PC is stored as a plain 16 bit value. However, in the MSP430X core the 20 bits are a bit intertwined with the status register, see the architecture manual for details.