5 HP BIOS
BIOS Addresses
| There are three major interrupt modes available: |
| PIC mode: This “Legacy” mode uses only the interrupt controllers. |
| Therefore, only one processor can be supported in this mode. This mode |
| can be selected upon installation of Windows NT. |
| Virtual wire mode: This mode is implemented using the 82C59 interrupt |
| and the I/O APIC controller and is used during boot time. The virtual wire |
| mode allows the transition to the “symmetric I/O mode”. In the virtual wire |
| mode, only one processor executes operations. |
| Symmetric I/O mode: This mode is implemented using the I/O APIC |
| controller and allows for multiple processor operations. |
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NOTE | In “PIC mode” and “virtual wire mode”, the PCI interrupts are routed to the |
| INT line. In the “symmetric I/O mode”, the PCI interrupts are routed to the |
| I/O APIC controllers and forwarded over an APIC bus to the processors. |
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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 page 59 for a table of the PCI device interrupts.
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