Lpc2000

At 07:46 PM 1/7/05 +0000, you wrote:
> > Well, you could read it into Philps SW and have calculate the
>checksum and
> > write in back out again.  I think that works anyway.  I'm not sure
>I see
> > the point though.
>
>Well the IAP updater that I'm working on reads the hex file and
>reprograms the lpc with the new code.
>
>If u look at the hex file example...
>:1000000018F09FE5FEFFFFEAFEFFFFEAFEFFFFEAB2
>:10001000FEFFFFEAFFFFFFFFF0FF1FE500F09FE597 <---0x0014 is "FFFFFFFF"
>:10002000A48C000028950000FFFFFFFFFFFFFFFFEB
>
>...my concern is that the vector checksum in the hex file isn't
>generated. I'd rather have the IAP updater do a vector check (before
>programming the reset block) instead of just calculating & storing
>the vector sum. The latter seems to assume that there are valid jump
>commands in the reset block.

OK, but a valid checksum won't be any assurance that the jumps are 
valid.  That'll just mean that something may have calculated the 
checksum.  The tool (whatever its is) that does the checksum calculation 
could have been fed an invalid file as easily as the updater.

If you want to only use verified files then I'd think about encapsulating 
them with a whole file check (CRC, MD5 or something similarly robust).  You 
could even use some sort of cryptographic checksum with your own key so 
that it was difficult to forge.

I'm thinking that the validity check (and checksum calculation come to 
that) should be done by the download program not the micro (for that 
matter, that's the way the ISP programs do it).

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III