Mike Sweeney msweeney77@gmail.com
Sun Jun 3 23:51:00 GMT 2007

On 6/3/07, Andrew Lunn <andrew@lunn.ch> wrote:
> On Sun, Jun 03, 2007 at 11:10:07AM -0400, Mike Sweeney wrote:
> > Can someone please explain to me what CYGHWR_HAL_ROM_VADDR is used for
> > in the ARM HAL? I see the comment about it in vectors.S but it makes
> > no sense to me. It further confuses me because it affects the
> > UNMAPPED_PTR macro which is only used when setting up the reset vector
> > and not the other exception vectors. Can someone shed some light on
> > what problem this solves?
> Think about how the system works when at boot time the ROM is at
> 0x0. Then early in the boot sequence the ROM is remapped to a high
> address and RAM is mapped to 0x0. Applications which run in ROM have
> to be linked with the high address, but the first part of the boot
> code, in particular the reset vector, needs to be linked for 0x0. If i
> remember correctl, CYGHWR_HAL_ROM_VADDR is involved in this.
>         Andrew

Thanks for the reply. I figured that's what it is there for, but I
don't understand based on how it is being used in the existing HAL
code how it actually works to fix that issue. I don't understand how
the UNMAPPED macro trickery works. An explantation of an existing
platform that uses this would be great.

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