Compaq 850 manual System Resources, Maskable Interrupts

Technical Reference Guide

4.4SYSTEM RESOURCES

This section describes the availability and basic control of major subsystems, otherwise known as resource allocation or simply “system resources.” System resources are provided on a priority basis through hardware interrupts and DMA requests and grants.

4.4.1 INTERRUPTS

The microprocessor uses two types of hardware 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, although it may be inhibited by hardware or software means external to the microprocessor.

4.4.1.1Maskable 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-H (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 4-9 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.

	IRQ3..7,	I/O Controller
	9..12,
I/O &	14,15		Interrupt	Serial IRQ
SM Functions			Serializer
IDE
	IRQ14,15
Hard Drives
PCI Peripherals	INTA-..D-

82801

ICH2

Interrupt

Processing

INTR-

APIC Bus Microprocessor

Figure 4-9.Maskable Interrupt Processing, Block Diagram

The 82801 ICH2 component can be configured (through the Setup utility) to handle interrupts in one of two modes of operation:

♦8259 mode

♦APIC mode

Compaq Deskpro EXS and Workstation 300 Personal Computers 4-15

Featuring the Intel Pentium 4 Processor

First Edition - December 2000