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Chapter 4 System Support
Compaq iPAQ Family of Internet Devices
First Edition - March 2000
4-12
4.4 INTERRUPTS
The microprocessor uses two types of interrupts; maskable and nonmaskable. A maskable
interrupt can be enabled or disabled within the microprocessor by the use of the STI and CLI
instructions. A nonmaskable interrupt cannot be masked off within the microprocessor but may
be inhibited by hardware or software means external to the microprocessor.
4.4.1 MASKABLE INTERRUPTS
The maskable interrupt is a hardware-generated signal used by peripheral functions within the
system to get the attention of the microprocessor. Peripheral functions produce a unique INTA-D
(PCI) or IRQ0-15 (ISA) signal that is routed to interrupt processing logic that asserts the
interrupt (INTR-) input to the microprocessor. The microprocessor halts execution to determine
the source of the interrupt and then services the peripheral as appropriate.
Figure 4-6 shows the routing of PCI and ISA interrupts. Most IRQs are routed through the I/O
controller, which contains a serializing function. A serialized interrupt stream is applied to the
82801 ICH.
Figure 4-6.
Maskable
Interrupt Processing, Block Diagram
The 82801 ICH component, which includes the equivalent of two 8259 interrupt controllers
cascaded together, handles the decoding of the serial interrupt stream (Serial IRQ signal) as well
as interrupts IRQ14 and 15 from the IDE hard drives. The ICH also receives the PCI interrupt
signals (INTA-..INTD-) from PCI devices. The PCI interrupts can be configured by PCI
Configuration Registers 60h..63h to share the standard ISA interrupts (IRQn). The power-up
default configuration has the PIRQn disabled. Table 4-13 lists the standard source configuration
for maskable interrupts and their priorities. If more than one interrupt is pending, the highest
priority (lowest number) is processed first.
The 82801 ICH is configured to handle interrupts in 8259-mode.
82801
ICH
Interrupt
Processing
Serial IRQ
IRQ14,15
INTA-..D-
IRQ3..7,
9..12,
14,15
IDE
Hard Drive
INTR-
Microprocessor
I/O and
SM Functions
PCI Peripherals
LPC47B277
I/O Cntlr.
Interrupt
Serializer