--- In lpc2000@yahoogroups.com, Michael Johnson <mpj@r...> wrote:
> >
> >ARM Application Note 31 talks about debugging directly from RESET, so
> >it *can* be done. I am just getting started using Phillip's products,
> >but I used to work for a chip manufacturer that used embedded ARM
> >cores, and we also had problems with our earlier reference design
> >circuit boards debugging from RESET. The ARM7TDMI can be debugged
> >directly from reset, but it does take a correct circuit board and JTAG
> >pod design to do it since JTAG has to come out of RESET before ARM
> >comes out of reset accord to AN31. After we reworked our reference
> >design circuit board hardware, we were able to debug software out of
> >reset. That was a really critical necessity at the time, since we had
> >some write once registers for system configuration that needed to be
> >written to very early in the normal boot sequence. If they were
> >written before the debugger got control, it was too late to debug any
> >difficulties related to that part of the system configuration.
> >
> >
> I know that other ARM devices/boards can be debugged from reset, we
have
> quite a few of them. Perhaps the LPC2xxxx boards we have (made by
> theARMPatch, IAR, Olimex, Keil and Nohau) have all got the reset wiring
> wrong - but I doubt it.
>
> Regards
> Michael
>
Are you using the same JTAG debugger pod on the ARM devices/boards
that will debug out of RESET? I have always been under the impression
that ARM does not give licensees a lot of latitude in altering the
functions of the cores they license, so it is dificult to imagine why
it does not work with Phillip's parts.
FWIW, I have just started playing around with an Embest board and
JTAG, and it will not debug out of reset either. According to the
schematic of the Embest board, they do not have the necessary logic
indicated in AN31, so should be impossible to debug out of RESET.
It is fairly certain in any case, that reset debug hardware would
certainly not be included in the final application hardware. It costs
money and space and is only useful in the specific instance of
debugging out of RESET. We only included it on the reference designs
and development hardware.
What is it about Phillip's ARM7TDMI that cause you to "doubt" the
accuracy of their ARM implementation? It seems much more likely that
the required external circuitry was simply not provided, since it is
*almost* never needed.
--Dave