©Richard L. Goldman1

IRQInterrupt Requests

(Static Presentation)

©Richard L. Goldman

April 25, 2002

©Richard L. Goldman2

Hardware Interrupts

• Hardware interrupts are signals from different devices in the computer.

• The interrupts are sent along dedicated traces to the CPU.

• When the CPU receives an interrupt is stops the job that it is doing and saves it in a memory stack.

• The CPU then processes the job associated with the interrupt.

• The interrupts and other CPU job are processed in order according to an established priority.

• Several jobs may be stored in memory stacks while higher priority jobs are being run.

©Richard L. Goldman3

IRQ Assignments

IRQ # Assignment IRQ

# Assignment

0 System Timer 8 Real-time Clock

1 Keyboard 9 NIC

2 2nd IRQ Controller 10 USB

3 Com 2 & 4 (Int. Modem) 11 SCSI

4 Com 1 & 3 12 System Mouse

5 LPT 2 or Sound Card 13 Math Coprocessor

6 Floppy Disk 14 Primary IDE (C: Hard Drive)

7 LPT 1 (Printer) 15 Secondary IDE (CD-ROM)

Set FunctionStandard FunctionRecommended Use

©Richard L. Goldman4

Sys TimerKeyboard

RTC

Math CP

CPU

32 Bit PCI Slots

8 BitISA Slots

16 BitISA Slots

USBSystemMouse

LPT 1

LPT 2Parallel Ports

FDD

Serial PortsCom 2 Com 1

01234567

Interrupt Controller

8259 (#1)INT

89101112131415

Interrupt Controller

8259 (#2)

INT

PrimarySecondary

IDE Channels

ABCD

PC

I Controller

IRQ Steering

IRQ Wiring

SCSIController

©Richard L. Goldman5

Interrupt Dialog

CPU MemoryHardwareDevice

(modem)

IRQ#3(I need attention) Who is assigned IRQ#3 ?

IRQ#3 is the Modemat I/O address 0FEEFA

I/O address 0FEEFA - ACK(modem, what do you want)

INT 6(Do my handler program #6)

Get and run handler atAddress 0FC2F7

InterruptVector Table

Where is modem handler #6 stored?

Modem handler #6 is atmemory address 0FC2F7

©Richard L. Goldman6

IRQ Priorities

IRQ #

Priority Assignment IRQ #

Priority Assignment

0 0 System Timer 8 2A RTC

1 1 Keyboard 9 2B NIC

2 --- Above 7 IRQs 10 2C USB

3 3 Com 2 & 4 11 2D SCSI

4 4 Com 1 & 3 12 2E System Mouse

5 5 Sound or LPT 2 13 2F Math CP

6 6 Floppy Disk 14 2G Primary IDE

7 7 LPT 1 15 2H Secondary IDE

©Richard L. Goldman7

IRQ Assignment Review

IRQ # Assignment IRQ

# Assignment

0 Sys Time 8 RTC

1 KB 9 NIC

2 --- 10 USB

3 Com 2 & 4 11 SCSI

4 Com 1 & 3 12 Sys Mouse

5 Sound / LPT 2 13 Math CP

6 FDD 14 P IDE

7 LPT 1 15 S IDE

©Richard L. Goldman8

IRQ Assignment Quiz

IRQ # Assignment IRQ

# Assignment

0 8

1 9

2 10

3 11

4 12

5 13

6 14

7 15

©Richard L. Goldman9

ISA & PCI Bus Signaling

PCI interrupts useLevel-sensitive Signaling

Off

Slot 1

Slot 2

Slot 3

Slot 4

5 VDC

4 VDC

3 VDC

2 VDC

0 VDC

ISA interrupts useEdge-triggered Signaling

Off

On

0 VDC

5 VDC

•ISA interrupts must use one trace for each interrupt.

•Many different PCI interrupts can use the same trace.

•Most all PCI devices share PCI interrupt A.