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Re: Memory Map conventions
- From: Grant Likely <glikely at gmail dot com>
- To: Mark Salter <msalter at redhat dot com>
- Cc: ecos-discuss <ecos-discuss at sources dot redhat dot com>, kevin dot cabral at gdcanada dot com
- Date: Tue, 18 Jan 2005 10:28:59 -0700
- Subject: Re: [ECOS] Memory Map conventions
- References: <528646bc0501180856c62333c@mail.gmail.com> <1106068131.12939.7.camel@gienah.localdomain>
- Reply-to: Grant Likely <glikely at gmail dot com>
On Tue, 18 Jan 2005 12:08:51 -0500, Mark Salter <msalter@redhat.com> wrote:
> On Tue, 2005-01-18 at 09:56 -0700, Grant Likely wrote:
> > The IXP reset code enables the MMU and inserts one-to-one mappings of
> > the physical address to virtual addresses. In other words, FLASH
> > stays at 0x50000000 and SDRAM stays at 0x00000000.
>
> Actually, IXP flash is located at 0x00000000 at reset. The early init
> code will switch it to the 0x50000000 physical address.
>
> >
> > On the PXA, the physical memory map is as follows:
> >
> > FLASH based at 0x00000000
> > SDRAM based at 0xA0000000
> >
> > However, the PXA reset code (at least for the uE250) does something
> > different. Rather than a one to one mapping from virtual address to
> > physical address, the MMU setup goes through contortions to remap
> > SDRAM from 0xA0000000 to 0x00000000 and remap FLASH from 0x00000000 to
> > 0x50000000. This makes the ROM/RAM addresses look the same as on the
> > IXP platform. However, it makes the bootup code complex and the
> > current code cannot support ROMRAM images.
>
> Why wouldn't ROMRAM images work?
Not that they wouldn't work, just that it doesn't look like the
current uE250 boot code supports ROMRAM images. I cannot find any rom
to ram copy code to support a ROMRAM image.
>
> > (In fact, from what I
> > understand it doesn't look like ROM images will work properly either
> > because I cannot find the copy from ROM to RAM).
> >
>
> Copy of .data sections?
Yea, I know; I wrote the wrong thing here. (got distracted). I did
find the copy of the .data section. What I meant to say was I didn't
understand how the PC followed FLASH moving from it's physical address
to it's virtual address.
> Life is easier if you put RAM at 0x00000000. This allows RedBoot to
> write to the cpu exception vectors.
>
> --Mark
>
Thanks
g.
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