> Clever boot loaders don't use interrupts.  This allows the
> app to use them without restriction.

Yes, but when the (midrange) app starts at 5, where does its interrupt
start?

> However, a boot loader needs to be the first thing that runs
> since it must
> be able to conditionally run the app.  I therefore don't see any way
> around the boot loader needing to own the reset vector.  I
> usually define
> an official start location for the app, like 4 words from the
> end of the
> first code page or the start of the second code page so that it won't
> cause additional fragmentation.  The boot loader jumps to
> this location
> only after deciding it's OK to run the app.

My bootloaders indeed take over the reset vector, but they relocate the
'stolen' instructions in a way that is in most cases transparent to the
application.

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products

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