Adam, that's not so.  If internal reads are diabled, then the entire chip is
locked for good.  If they crack the bootloader, they are only going to get
the code that "patches" what's there already.  They'll get fragments only,
in the best case.  The truth is they;ll drop the effort and just try to
emulate from scratch.  And that they can do no matter what.

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of M. Adam Davis
Sent: Thursday, July 26, 2001 9:20 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: FINAL WORD: A great solution for the PIC16F877
problems (code protect,bootloader)


Sorry, I mis-read the original statement.

Disabling the internal reads is not necessary, as long as external reads
and writes are disabled.

The reason the idea of disabling internal reads came up is that someone
could write code using icsp to read out the internal memory.  If you
can't read or write code to the chip except through secure bootloader,
then internal reading becomes secure.  So it's really a moot point.

-Adam

Byron A Jeff wrote:

>On Thu, Jul 26, 2001 at 08:12:15AM -0400, M. Adam Davis wrote:
>
>>Ideally the code protect (including the ICSP disable) would occur AFTER
>>the verify.
>>
>
>This is not possible. When programming the chip with internal writes, the
>config word is inaccessible. You can't change any of the config bits. That
>can only be done when programmed externally.
>
>What Ron proposes is a black hole. You have to trust that the write works
>correctly.
>
>BAJ
>
>>-Adam
>>
>>wouter van ooijen & floortje hanneman wrote:
>>
>>>>>Very simple:  Allow me to disable ICSP reads no matter what, and allow
me
>>>>>
>>>>to
>>>>
>>>>>disable internal reads of the flash memory, but allow internal flash to
>>>>>
>>>be
>>>
>>>>>re-written.
>>>>>
>>>Bad idea, how would you VERIFY?
>>>
>>>Wouter
>>>
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