Lpc2000

derbaier wrote:

>--- In lpc2000@yahoogroups.com, Michael Johnson <mpj@r...> wrote:
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>>>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
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>have 
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>>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
>>
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>>
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>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. 
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Yes.

>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.
>
>Mostly the fact that we don't have any boards that work correctly. I would have expected one of the board vendors to get it right - the information from ARM is clear. I can also see that having code that runs from reset (with debugging disabled) before the user application code enables a silicon vendor to create many product variants.
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Regards
Michael

>--Dave
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