Johan Forslöf

Stack top overwritten while single-stepping

Discussion created by Johan Forslöf on Jun 1, 2012

As the title suggests I'm having trouble with the stack seemingly getting trashed by the debugger. This happens with the built-in SofTec debugger of my DEMO9S12XSFAME board and a freshly installed Code Warrior 5.1.

More specifically it only happens with interrupts globally enabled in the MCU and the debugger set to ignore maskable interrupts.


Here's a repro case. Install it as the main file of a default 9S12XS128 C project, select the SofTec debugger, configure it to disable maskable ISR's, and try stepping through the loop.


#include "hidef.h"void failure(void *__far ptr, char stay) { volatile int dummy = (unsigned long) ptr >> 16; do  ++dummy; while(stay); // Generated code: /* STAB 3,-SP <- Stores the argument at $20F4 LDX  7,SP LDAB 6,SP CLRA STD  1,SPloop: INCW 1,SP <- Trashes $20F4 w. $C4 LDAB 0,SP BNE  loop LEAS 3,SP RTC */}void main(void) { EnableInterrupts; failure(NULL, 0);}