locore.S question
Mark Tinguely
tinguely at casselton.net
Tue Mar 31 16:50:17 PDT 2009
> On Wed, Mar 25, 2009 at 03:06:49PM +0100, Guillaume Ballet wrote:
> > Hello list,
> > I'm working on a FreeBSD port for the BeagleBoard. I'm starting the
> > kernel with u-boot and wrote my own small loader for this purpose.
> > That loader puts the kernel at 0x81000000 (physical address, since the
> > MMU is disabled at this stage).
>
> Nice to hear you're working on that port :)
>
> > In locore.S, however, there is the following piece of code that is
> > executed before the MMU is disabled:
> >
> > 112 adr r7, Lunmapped
> > 113 bic r7, r7, #0xff000000
> > 114 orr r7, r7, #PHYSADDR
> >
> > (snip, disabling MMU)
> >
> > 129 mov pc, r7
> >
> > Since PHYSADDR is set to 0x80000000 (physical start of RAM), then r7
> > is set to 0x80000000 + offset(Lunmapped) instead of 0x81000000 +
> > offset(Lunmapped). Of course it crashes.
> >
> > Now, bypassing the problem is relatively easy, but still I was
> > wondering why it is 0xff000000 instead of 0xf0000000 on line 113?
I was wondering why the kernel is loaded 16MB into the physical memory?
--Mark.
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