Table 4-8. Maskable Interrupt; Table 4-9. Maskable Interrupt; Apic Mode - Compaq Deskpro Workstation AP230 Technical Reference Manual

Chapter 4 System Support
8259 Mode
The 8259 mode handles interrupts IRQ0-IRQ15 in the legacy (AT-system) method using 8259-
equivalent logic. Table 4-8 lists the standard source configuration for maskable interrupts and
their priorities in 8259 mode. If more than one interrupt is pending, the highest priority (lowest
number) is processed first.
Table 4-8. Maskable Interrupt Priorities and Assignments
Priority Signal Label
1 IRQ0
2 IRQ1
3 IRQ8-
4 IRQ9
5 IRQ10
6 IRQ11
7 IRQ12
8 IRQ13
9 IRQ14
10 IRQ15
11 IRQ3
12 IRQ4
13 IRQ5
14 IRQ6
15 IRQ7
-- IRQ2

APIC Mode

The Advanced Programmable Interrupt Controller (APIC) mode provides enhanced interrupt
processing with the following advantages:
Eliminates the processor's interrupt acknowledge cycle by using a separate (APIC) bus
Programmable interrupt priority
Additional interrupts (total of 24)
The APIC mode accommodates eight PCI interrupt signals (INTA-..INTH-) for use by PCI
devices. The PCI interrupts are evenly distributed to minimize latency and wired as follows:
ICH2
Int. Cntlr.
INTA-
INTB-
INTC-
Wired
INTD-
INTE-
INTF-
INTG-
INTH-
NOTES:
[1] Connection internal to the ICH2. Will be reported by BIOS as using INTA but is NOT shared with
other functions using INTA.
[2] Internal graphics controller of the 82815 GMCH, internally wired.
Deskpro SDT and CMT systems only.
4-16 Compaq Deskpro Personal Computers
Maskable Interrupt Priorities and Assignments
Source (Typical)
Interval timer 1, counter 0
Keyboard
Real-time clock
Unused
Unused
Unused
Mouse
Coprocessor (math)
IDE primary I/F
IDE secondary I/F
Serial port (COM2)
Serial port (COM1)
Unused
Diskette drive controller
Parallel port (LPT1)
NOT AVAILABLE (Cascade from interrupt controller 2)
PCI PCI PCI
Slot 1 Slot 2 Slot 3
INTA- INTD- INTC-
-- --
INTB- INTA- INTD-
-- --
to
-- --
INTC- INTB- INTA-
INTD- INTC- INTB-
-- --
Third Edition – April 2001
Table 4-8.
PCI PCI
Slot 4 Slot 5
INTB- INTD-
-- -- --
INTC- INTA- INTA-
-- -- -- INTB-
-- -- ---
INTD- INTB-
INTA- INTC-
-- -- --
AGP NIC USB
Slot I/F [1] I/F #2
-- -- --
-- -- --
-- --
-- --
-- INTA- --
-- -- --
-- -- --
-- -- INTC-
Direct AGP
Cntlr. [2]
INTA-
INTB-
--
--
--
--
--
--