HP X Class 500/550MHz, Reference Manual

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108 Chapter 4
HP BIOS
BIOS Addresses
There are three major interrupt modes available:
1. PIC mode: This “Legacy” mode uses only the 82C59 interrupt controllers. Therefore,
only one processor can be supported in this mode. The system can be forced to operate
in this mode by selecting “mono-processing” in the system setup.
2. Virtual wire mode: On the HP V
ISUALIZE
Personal Workstations, this mode is
implemented using the 82C59 interrupt and the I/O APIC controller 82093AA. This
mode is used during boot time, if the choice “multi-processing” has been selected in the
system setup. The virtual wire mode allows the transition to the “symmetric I/O mode”.
In the virtual wire mode, only one processor operates.
3. Symmetric I/O mode: This mode is implemented using the I/O APIC controller 82093AA
and allows the operating system to perform Symmetric Multi-Processing (SMP)
operations (refer also to item 2 above). For further information about Multi-Processing,
refer to the section “Configuring Setup For Multi-Processing” in the chapter “System
Board.”
NOTE In “PIC mode” and “virtual wire mode”, the PCI interrupts are routed inside
the 82C59 to ISA interrupts. In the “symmetric I/O mode”, the PCI and ISA
interrupts are used by the 82093AA and are handled in a separate manner.
PCI Interrupt Request Lines
PCI devices generate interrupt requests using up to four PCI interrupt request lines
(INTA#, INTB#, INTC#, and INTD#).
PCI interrupts can be shared; several devices can use the same interrupt. However,
optimal system performance is reached when minimizing the sharing of interrupts. Refer
to the section “Devices on the PCI Bus” in the chapter “System Board” for a table of the
PCI device interrupts.