On Sat, 07 Oct 2000, Alstrup, Kurt wrote:
> Thanks for the info.
>
> The SA-1100 and IXP-1200 (the StrongArm core of the latter) both have the
> same MMU instructions as eg SA-110 has.
>
>  The problem is that the hardware I know (SA-110 + 21285 co-processor has
> it's RAM at address 0 and ROM somewhere else. This works only because the
> 21285 (aka footbridge) maps (they use the term alias in the specs) the ROM
> to address 0 in the time-window after reset and the first memory write.
> That window is enough to jump to the true ROM where the remainder of the
> bootstrap happens.
>
>  The IXP1200 does not (to my knowledge) perform that little trick, so my
> concern is if NetBSD has any dependencies/requirements regarding the
> physical
> location of ROM and RAM (e.g. must RAM be at address 0).

Hmmm, I'm sure that at some point we remap the kernel into the 0 page.  if 
you can do this with the MMU then you'd have rom at 0, this loads up the 
kernel into the ram, then calls the kernel (calling it's address would be 
like calling it's reset vector)  it could then map itself down into the 0 
page?

I don't know enough about the MMU to say if this is possible.

As for the IXP1200 surely the same trick could be done with hardware as with 
the footbridge?  all it is is something that gets reset on the reset pin, and 
then remaps on the first write pin high?

> I am tempted to put ROM at address 0 and RAM somewhere else. The reset
> vector would point at the ROM and the other vectors just re-direct to the
> bottom of the physical RAM. If this will work, then the next question is
> what configuration files need to be adjusted?

That would certainly sound possible.  Do you have a bootstrap rom already to 
try these things out?  (I hate to say it but it might be a case of play with 
some code and see if you can get it to do something?)

What is the IXP-1200 anyway?  is this part of intels new chip range base on 
the SA, I'm sure I saw an article on slashdot about a new chip range (called 
Xscale?)
http://slashdot.org/articles/00/08/25/1155254.shtml

Chris