According to the ACPI spec, The FADT (Fixed ACPI Description Table) table contains a field that reports the SCI interrupt number to OS. The field is defined as below:
I dumped the FADT table on an Intel x86 platform and see the SCI interrupt is associated with the number 9:
But according to the Intel Manual, 0-31 are reserved vectors for IA architecturally defined interrupts. Specifically, the 9 is defined as:
So, according to the note, the 9 is not generated after I386 processor. So I guess that's why 9 can be salvaged for SCI. This can be seen as a x86-specific implementation of the ACPI spec.
Am I right on this?
ADD 1
Seems I misunderstand something here. Will update later.