Hiya,

Should I post the source code I created from the ICD download on my web
page?  I held off because seeing the code is one thing, but you do not see
how the ICD box interfaces to it (there is a *lot* of communications
including resets going on there).

Before I post it, I want to change the registers (0x018E and 0x018F) to the
Microchip specified names.

> > Hi Bob, hi Myke, and others interested in ICD
> >
> > Another question:
> >    The ICD code do not allow nested routines? According to DS51242A,
> > a RETURN will cause the clear of the INBUG bit and "warms" peripherals
> > freezed by FREEZ bit. (I think that more flexible will be if Microchip
> > creates a new specific instruction, like "RETURN_FROM_ICD"
> > instead a general-purpose RETURN).
>
> Yes, that is how I read it.

This "feature" makes it quite challenging to code for the ICD and when you
take a look at the source for the ICD (on the targe PICmicro), it can be
quite difficult to understand.

When I played around with the ICD, trying to "clean up" the code on my own,
I discovered this aspect of the debugger.

Personally, I don't know how much importance I would place on a separate
instruction since there is really only 256 instructions that you can play
with and I want to see what I can come up with on my own, but I will
probably use the Microchip code simply because I have invested quite a bit
of time understanding it.

>  > Another more interesting thing:
> >    Is necesary to write a GOTO  DEBUG_CODE in the configuration zone (at
> > position
> > 0x2004)? In certain situation, the PC points to 0x2004 (beyond the
program
> > memory)
>
> Yeah, I guess so. But something is fishy here because nothing is being
done
> with PCLATH!

I don't understand this either.  I suspect that if ICD mode is selected in
the configuration registers this address becomes a new reset vector.

> >  But, I dont understand why, in another situation, if a HALT
> > signal is asserted the PC points to 0x0001. (Section 2.7 to 2.7.2 )
>
> Its because of the way the breakpoint is implemented. The breakpoint
address
> register is initialized to zero. If external HALT is asserted as we come
out
> of reset the device will automatically take a breakpoint, BUT the
breakpoint
> is always taken AFTER the instruction executes, hence the PC will be
0x0001.
> That's why mChip tells you to put a NOP in location 0: so that you can
> really start single stepping your programming from location 0x0001.
>
> > What do you have discovered about it? DS51242A is confusing, I think.
>
> It certainly is.

I have spent about fifteen hours with an oscilloscope and burning different
code into the chip to see how it works.

It actually isn't that confusing - but it is limited.  I feel like there
should be ways of enhancing its capabilities (ie being able to access the PC
stack), but I don't know.

myke

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