[ECOS] how does processor finds redboot image ?

Andrew Lunn andrew@lunn.ch
Thu Mar 17 17:13:00 GMT 2005


On Thu, Mar 17, 2005 at 06:14:36AM -0500, Sumit Chauhan wrote:
> Hi,
> 
> thanks for your reply, I understand most of it -;)
> I didnt knew basically that by default ARM maps flash at 0x00000000 ,
> anyways, but / so if my redboot is in ROM mode .. redboot_ROM.ecm was
> used, will it keep on executing from flash only ? is this remapping
> done only for ROMRAM, RAM modes I believe,as else we would have been
> able to write the flash anyways -:)

ROM applications execute from ROM. The only exception is when using
the FLASH functions which run from RAM. They have to because you
cannot execute from FLASH while erasing/programming it.

ROMRAM goes through the same mapping process. It then copies itself
from ROM into RAM and then jumps into the RAM copy.

RAM versions do not touch the memory setup. They assume something else
has already do that.

        Andrew


> 
> Sumit
> 
> 
> On Thu, 17 Mar 2005 12:05:41 +0100, Andrew Lunn <andrew@lunn.ch> wrote:
> > On Thu, Mar 17, 2005 at 05:26:16AM -0500, Sumit Chauhan wrote:
> > > Hi,
> > >
> > > I have a very basic question and hopefully will answer this,
> > > when a processor reset happens, say as in case of IXP425 it starts pc
> > > at 0x00000000 , Then how does it starts loading redboot from flash ??
> > > or does as in my case redboot image is a ROM based, it just shifts it
> > > execution to flash start sector and XIP ?
> > 
> > I don't know about this specific processor, but in general the ARM
> > maps the FLASH to address 0x0 at startup. eCos ROM startup mode then
> > arranges to have the FLASH remapped to higher memory and then eCos
> > jumps to the higher memory copy of itself. It then puts RAM at address
> > 0x0.
> > 
> >         Andrew
> >
> 
> -- 
> Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
> and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
> 

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