> Harold Hallikainen wrote:
>> I wrote a bootloader for the 24H. CodeGuard is interesting. Once code
>> protect is enabled for the bootloader, the general segment can only call
>> code in the first 32 words (or something like that) of the boot segment.
>> Anything else will cause a fault. Also, interrupt vectors are redirected
>> when the processor is executing in the boot segment. My bootloader is a
>> web post bootloader, so it uses the TCP/IP stack to put the new code in
>> external flash, then copy the external flash to internal. The code to
>> deal
>> with internal and external flash are in the boot segment. Since it would
>> be possible to bootload bad code into the general segment that would
>> then
>> keep the TCP/IP stack from running (and preventing further bootloads), I
>> have another copy of the original code (factory installed) in the
>> external
>> flash. Inside the box, you short two pins on a header and power the unit
>> up to reload that original code.
>>
>> So, CodeGuard is interesting. A bit of a pain to work with if you have
>> to
>> call the boot segment from outside or are using interrupts.
>
> So does this mean that you don't encrypt the updates? This was the second
> part of my original question. :)
>
> Vitaliy

Yes, this means I don't encrypt updates. Updates are emailed to individual
technicians in the field instead of being put on a website. There is the
danger of them being passed around, but I don't think it's worth while for
someone to reverse engineer our hardware. I may want to do some sort of
encryption in the future. I know Microchip has a library for that, but
have not looked at it.

Harold


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