在 2013-03-06三的 10:07 +0100，Paolo Bonzini写道：
> Il 06/03/2013 09:56, Hu Tao ha scritto:
> >> >
> >> > Something like this should work (in SeaBIOS's src/acpi-dsdt-isa.dsl):
> >> >
> >> > Device(PEVT) {
> >> > Name(_HID, EisaId("QEMU0001"))
> >> > OperationRegion(PEOR, SystemIO, 0x505, 0x01)
> >> > Field(PEOR, ByteAcc, NoLock, Preserve) {
> >> > PEPT, 8,
> >> > }
> >> >
> >> > Method(_STA, 0, NotSerialized) {
> >> > Store(PEPT, Local0)
> >> > If (LEqual(Local0, Zero)) {
> >> > Return (0x00)
> >> > } Else {
> >> > Return (0x0F)
> >> > }
> >> > }
> > IIUC, here _STA reads from ioport 0x505, if the result is 0, then the
> > device is not present. Otherwise, the device is present. But as Gleb
> > said, ''the data you read from unassigned port is not guarantied to be
> > zero, it may depend on QEMU version''. What should I do to tell if the
> > device is present or not correctly?
>
> The firmware is tied to the QEMU version, so you can rely on unassigned
> ports returning zero.
>
but what if we happen to transfer data end by 0x0,
here, will this device(QEMU0001) disappear?
(by this asl code snippet, I think it will)
so, if we transfer data(not 0x0) device appear,
then, it will disappear(if come across 0x0),
can this happen?
or should we use another status io port e.g.
0x506 to handle this condition?
> Later we can change this to use fw-cfg.
>
> Paolo
>
>
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