Odd situation on a PIC 16F872:  Still coding the pet feeder and things
were going along quite nicely, until I added a piece of code and everything
freaked out.  When it normally starts up, the (4) 7-seg digits show '_'
and then goes in to clock mode, counting from 00:01 upwards.  With
the new piece of code it shows the start-up underscores, then freezes.
However, the code is still running.  I know this cause I can press the
buttons and get some actions out of them (though some behaviors
an incorrect now).  Also added a blinking LED within the ISR and
that shows up even when the code is broken.  No WDT.

So I commented out the new code (subroutine) and it works again, BUT
if I comment out the code that calls the new subroutine (but leave the
subroutine in place), it still does NOT work.  I've narrowed it down to the
existence of the code that causes a problem.  I've even changed the new
subroutine to 26 nop's (instead of the 26 instructions that were there) with
absolutely no calls to it, and it still fails.

So now I look at page boundaries, but my total code size is under 600
bytes, and I should not have to worry about paging on a 2K-prog-memory
'F872.  Another check for tables crossing the 256-byte boundary and no
violations there.  Also using indirect addressing in various places, but
all addresses pointed to are in bank 0 of data mem so that should not
be a problem.

I skimmed thru the memory-organization chapter (ch 6) of the mid-range
mcu doc again and haven't come up with anything new that could be
causing this.

Some memory map info:
    Main code (init stuff and main loop): 0x0005 thru 0x00E2.
    Subroutines: 0x00E3 thru 0x0020E
    ISR:  0x020F thru 0x0244

What else could I be neglecting to check here?

My next test will be slowly reducing the 26 nops to see when the code
works again and see if that leads to anything.  After that I may reinstall
the MPLAB simulator and try it there.

Thoughts appreciated,
-Neil.

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