Re: Kernel executation from ROM

[ebiederm@xmission.com (Eric W. Biederman)]

Jeremy Jackson <jeremy.jackson@sympatico.ca> writes:

> Jaswinder Singh wrote:
> 
> > Dear Sirs,
> >
> > Thanks for your help,
> >
> > I see . The biggest negative point of running kernel from ROM is that ROM
> > speed is slow :(
> 
> Also, the PCI specification forbids executing code from ROMs over the PCI bus.
> The system BIOS in a PC is not on the PCI bus, bus, but everything else is.

No it forbids executing boot roms that way, by a standard pc bios.  
The system BIOS in a PC is normally on the ISA bus which is reached
across via the PCI bus with a PCI->ISA bridge.

The thing is slow it really doesn't matter, all you need to do is
enable caching on that area of the physical address space.  You can't
do this on the alpha currently but only because the alpha sucks that
way.  You can on practically everything else.

As for ROM being slow on x86 you can enable the MTRR to speed things
up.  Usually though ROMs are at least as expensive as RAM, so it is
pointless.

Eric