Re: gate A20 and i386-qemu port

[Robert Millan <rmh@aybabtu.com>]

On Sat, Nov 14, 2009 at 04:38:22PM +0100, Robert Millan wrote:
> > Following code can check A20:
> > *((volatile grub_uint8_t *) 0x200000) = 0;
> > *((volatile grub_uint8_t *) 0x300000) = 1;
> > if (*((volatile grub_uint8_t *) 0x200000))
> >   grub_printf ("Expect bugs\n");
> > else
> >   grub_printf ("You're safe\n");
> 
> Yeah, in fact we have gate_a20_check_state() to check for this, but only
> in i386-pc.
> 
> I find it surprising that i386-qemu works at all without it.  I guess it
> only works because the high mem area that would overlap with our code in
> 0x8200 is never used.
> 
> I'll look into this...

It appears that QEMU hardware already starts with A20 enabled.  I suppose it's
bochsbios who disables it.  In any case, I made my vbe-on-coreboot branch
enable it.

Unfortunately, this wasn't the cause that prevented vbetest/vbeinfo from
working :-/

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."