Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Table 5-67 GIC Interrupt Translation Service Structure
Field
Byte
Length
Byte
Offset
Description
Type 1 0 0xF GIC ITS structure
Length 1 1 16
Reserved 2 2 Reserved - Must be zero
GIC ITS ID 4 4 GIC ITS ID. In a system with multiple GIC ITS units, this value must
be unique to each one.
Physical Base 8 8 The 64-bit physical address for the Interrupt Translation Service
Address
Reserved 4 16 Reserved – Must be zero
5.2.13 Global System Interrupts
Global System Interrupts can be thought of as ACPI Plug and Play IRQ numbers. They are used to
virtualize interrupts in tables and in ASL methods that perform resource allocation of interrupts. Do
not confuse global system interrupts with ISA IRQs although in the case of the IA-PC 8259
interrupts they correspond in a one-to-one fashion.
There are two interrupt models used in ACPI-enabled systems.
The first model is the APIC model. In the APIC model, the number of interrupt inputs supported by
each I/O APIC can vary. OSPM determines the mapping of the Global System Interrupts by
determining how many interrupt inputs each I/O APIC supports and by determining the global
system interrupt base for each I/O APIC as specified by the I/O APIC Structure. OSPM determines
the number of interrupt inputs by reading the Max Redirection register from the I/O APIC. The
global system interrupts mapped to that I/O APIC begin at the global system interrupt base and
extending through the number of interrupts specified in the Max Redirection register. This mapping
is depicted in Figure 5-25.
There is exactly one I/O APIC structure per I/O APIC in the system.
154 April, 2015 Version 6.0