Am 28. März 2024 14:09:52 UTC schrieb Mark Cave-Ayland
<mark.cave-ayl...@ilande.co.uk>:
>On 27/03/2024 07:09, Gerd Hoffmann wrote:
>
>> On Tue, Mar 26, 2024 at 01:30:48PM +0000, Mark Cave-Ayland wrote:
>>> Heh I've actually been using isapc over the past couple of weeks to fire up
>>> some old programs in a Windows 3 VM :)
>>
>> I'm wondering why these use cases can't simply use the 'pc' machine
>> type?
>>
>> The early pci chipsets of the 90-ies have been designed in a
>> backward-compatible manner, with devices such as the IDE controller
>> being mapped to the standard ISA ioports. So even an historic OS which
>> does not know what PCI is can run on that hardware, by simply talking to
>> devices using the standard ISA io ports ...
>
>Hmmm that's a fair point: I think the pc machine has a PCI-ISA bridge
>included, so ISA devices can be plugged in as needed. The reason I ended up on
>that configuration was because I ended up chasing down a regression, and
>wanted to quickly eliminate things such as ACPI.
In theory you could pass `-M acpi=off` to not instantiate the PIIX4 ACPI
function, essentially turning the Frankenstein-PIIX4 SB into a PIIX3. However,
this also removes SMI registers used by SeaBIOS to handle SMM setup which may
create unwanted side effects. On a real PIIX3, these registers are located in
the ISA function. I wonder if it made sense to implement that for greater
compatibility.
What do you think? Gerd, what do you think w.r.t. SeaBIOS?
Best regards,
Bernhard
>
>
>ATB,
>
>Mark.
>
>
