RE: [ECOS] Redboot FIS directory block padding

["Koeller, T." <Thomas dot Koeller at baslerweb dot com>]

Gary,

I guess 'in-place compatible expansion' means being able
to add additional fields without changing the size of the
structure? What kind of compatibility are you trying to
achieve this way? The FIS directory entries are only used
by RedBoot internally. If I change their layout and re-compile
RedBoot, it still works as before. I also cannot see any reason
why it would be important that the in-memory layout of those
structs is identical across different systems.

If you think about making the FIS directory available to
programs external to RedBoot, then I'd say creating a FIS
API would be more appropriate than relying on a particular
FIS block layout, as has been proposed on this list recently.
Just adding new fields is pretty useless, there also has to
be a way for an application to determine if these additional
fields are actually present, so you woud have to add a
'version' or explicit 'size' field - which would affect the
layout.

Even with padding completly removed, there can be at most 5
entries per flash sector, assuming a sector size of 256. This
is still not too much, so it would be a good thing if the FIS
directory could span multiple sectors.

For all the reasons explained above, I still hold up my proposal
of completly removing the padding.

tk

> -----Original Message-----
> From: Gary Thomas [mailto:gary@chez-thomas.org]
> Sent: Tuesday, June 18, 2002 6:48 PM
> To: Koeller, T.
> Cc: 'ecos-discuss@sources.redhat.com'
> Subject: Re: [ECOS] Redboot FIS directory block padding
> 
> 
> There were two reasons for the padding:
>  1) to allow for in-place compatible expansion of the structure
>  2) to make it easier for other systems to stay compatible
> 
> Maybe 256 bytes is too large (64 might be better), but I'm against
> removing the padding altogether.
> 
> 
> 
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----------------------------------------------- 
Thomas Koeller, Software Development 

Basler Vision Technologies 
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22926 Ahrensburg 
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Tel +49 (4102) 463-390 
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