Advice and Suggestions for a Debug Feature

Tapley, Mark mtapley at
Wed Dec 16 10:04:29 CST 2015

On Dec 16, 2015, at 9:22 AM, Jerome H. Fine <jhfinedp3k at> wrote:

> Note that for many CPUs, adding values (a push) results in the
> stack pointer becoming numerically smaller (unsigned of course).
> Internally, the code would handle the actual arithmetic.

(Warning: assembly language noob talking, please disregard if I see to be making no sense.)

1) Does the debugger enhancement trigger a stop on overall size of stack pointer or on cumulative changes? Or could it be selectable (maybe via a negative argument?)

Here’s what I’m thinking: suppose a routine is expected to remove things from the stack sequentially, then branch at some point to a subroutine. I want the debugger to halt execution when it branches. So I want the stop to occur when the stack pointer first increases, even if it has already decreased several times and its new value (on branching) is lower than where it was when the debug command was issued.

2) Some machines (6809, which is the only one I’m familiar with) have a rapid-response branching mechanism for real-time control applications (on the 6809 it’s a Fast Interrupt input). Fewer registers are pushed onto the stack so the service routine can execute sooner. Is there a way to handle this situation? Say I expect two levels of subroutine calls, each stacking a full set of registers, but instead I get for the second subroutine a Fast Interrupt and don’t stack enough registers to trigger the debug counter to halt execution. 

	Hope this is useful.

							 - Mark

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