Re: [ECOS] XScale PXA255 MMU Translation Table Query

[Andrew Lunn <andrew dot lunn at ascom dot ch>]

On Wed, Jul 30, 2003 at 01:36:09PM +0000, Francis Musto wrote:
> On thinking about this, I think accesses to ROM & RAM will have to be 
> addressed to different locations after the MMU is enabled, I cant find any 
> mention of this in the examples I am using. Is this handled by ECOS in some 
> hidden way? Does it copy the ROM to RAM somewhere & jump to it after the 
> MMU is enabled & do RAM accesess need a different set of location defines?

There are two ways this can be done. 

For normal ROM startup applications, the startup code is written so
that its position independent. So it can run the code at both the low
and the high address. It then just has to jump from one to the other
as the MMU is configured.

The copying of ROM to RAM is called ROMRAM startup. Some targets
support this. This basically starts the same way as a ROM app, but
once the MMU is setup, it copies itself from ROM to RAM and then jumps
into the RAM copy. Again the position independent stuff allows this to
happen.

   Andrew

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