Re: [Qemu-devel] Support NEC PC-98x1 on QEMU

[Alexander Graf]

On 08.09.2009, at 11:41, 武田 俊也 wrote:

> Dear Stuart,
>
> > There's no need to add this as a whole new architecture, although
> > perhaps the use of TARGET_PC98 was only meant to be temporary...
>
> The problem is that now TARGET_I386 is used for both 2 meanings,
> cpu is i386 and the arch is PC/AT.

No, that's what the -M switch is there for. Admittedly x86 has rather  
few machine descriptions, but PC-98 really is just a "non-PC/AT"  
machine, so it belongs there.

[...]

> About A20 line gate:
>
> In PC/AT arch, only A20 line is masked and when cpu is reseted it is  
> not masked.
> You know, In PC-98x1 arch, A20 and upper lines are masked and when  
> cpu is reseted
> they are masked.
>
> Now A20 gate is hard-corded in i386 core, but it is only PC/AT  
> specifications
> probably by external circuts, not cpu internal.
> It may be possibly better to move a20 gate codes to pc.c and pc98.c,
> but I think it is allowable to keep them in cpu core with #ifdef for  
> each arch.

Sounds like that should be a config variable in the CPU description,  
so you can set the default CPU be "486,+a20mask" or so.

In general, all the changes should be runtime variable dependent, so  
the same binary can run PC/AT and PC-98.

Alex