[U-Boot] problem with mpc837x start.S

[Scott Wood]

On Wed, 3 Aug 2011 00:48:32 +0000
shawn Bai <programassem at hotmail.com> wrote:

> 
> 
> 
> ----------------------------------------
> > Date: Tue, 2 Aug 2011 10:21:09 -0500
> > From: scottwood at freescale.com
> > To: programassem at hotmail.com
> > CC: u-boot at lists.denx.de
> > Subject: Re: [U-Boot] problem with mpc837x start.S
> >
> > On Tue, 2 Aug 2011 04:11:25 +0000
> > shawn Bai <programassem at hotmail.com> wrote:
> >
> > > > When flash is enlarged to 4GiB, it repeats throughout the address space.
> > >
> > > After flash is enlarged to 4GiB, why will it repeat through the address space? the whole 4GiB address space?How does it happen?
> >
> > It's just how the hardware works -- the flash chip only sees the address
> > bits that are relevant to its size. The higher address lines can be
> There must be something needed to learnt by myself to understand "how the hardware works".
> And, when you mention "its size", you mean 8MBytes,or 4GiB?

If the flash is 8MiB (as determined by physical reality, not OR0), it only
decodes the low 23 bits of the address. The upper bits must hit in BR0/OR0,
but after that they are discarded.  So for example, if OR0 maps a 4GiB
window, 0x00123456, 0x00923456, 0xff123456, and 0xe0123456 all point to the
same location in flash, because the flash only sees 0x123456.

-Scott