[coreboot] About Paging, Realmode and what is going on

[Peter Stuge]

Philipp Stanner wrote:
> > > Why would I want to address memory in RM with 32 Bits? I don't see
> > > any difference to using PM without Paging enabled.
> > 
> > In a bootloader (after coreboot) you often want to call BIOS
> > interrupt services which assume real mode, because that was the
> > only mode, when the interrupt services were created.
> > 
> > For coreboot itself, I think there is little if any advantage to big
> 
> Wait. Coreboot doesn't implement BIOS-Interrupt-Services.

Sure, but a payload can. SeaBIOS aims to provide a complete BIOS with
all neccessary interrupt services for legacy compatibility.


> So no payload started by cb should ever try to call BIOS, should it?

That depends. A *payload* can not assume interrupt services, but a
bootloader (e.g. in MBR) can very well assume interrupt services, 
especially since MBR is a BIOS paradigm.


> And you can't use the 32-Bit-Instructionset anymore, can you?

That's orthogonal. You can use 32-bit instructions in 16-bit mode and
vice versa. The 0x66 and 0x67 opcode prefixes can be used to set an
instruction mode for a single instruction.


//Peter