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Transcript of 6 IRQ Controller
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Computer HardwareComputer HardwareUnit 20Unit 20
22ndnd Year National Diploma Year National Diploma
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Computer HardwareComputer Hardware
IRQ ControllerIRQ Controller
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Table of Contents Table of Contents
Simplified diagram of a modern DMA computerSimplified diagram of a modern DMA computer
IntroductionIntroduction
IRQsIRQs Interrupt ControllersInterrupt Controllers
Interrupt PrioritiesInterrupt Priorities
NonNon--Maskable Interrupts (NMI)Maskable Interrupts (NMI) Interrupt ConflictsInterrupt Conflicts
Summary of IRQsSummary of IRQs
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Simplified diagram of a modern DMA computerSimplified diagram of a modern DMA computer
CPU
Memory
Controller
I/O
Controller
DMA
Controller
IRQ
Controller
I/O
Devices
Storage
Devices
RAM
L2
Cache
Control Bus
System Bus
I/O Bus
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IntroductionIntroduction
When you install an expansion board in a slot, it When you install an expansion board in a slot, it
gets connected to the I/O bus.gets connected to the I/O bus.
The board can therefore send and receive data The board can therefore send and receive datato and from the I/O device.to and from the I/O device.
But who regulates the traffic?But who regulates the traffic?
Who gives clearance to the new controller to Who gives clearance to the new controller tosend data?send data?
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IRQsIRQs (1 of 6)(1 of 6)
To control data traffic on the I/O bus, the To control data traffic on the I/O bus, the
concept of concept of IRQ (IRQ (IInterruptnterrupt R R eeQQuest)uest) was was
created.created. A fundamental principle in the PC design. A fundamental principle in the PC design.
2 types of Interrupts:2 types of Interrupts:
Software InterruptsSoftware Interrupts
Used to call any number of BIOS routinesUsed to call any number of BIOS routines
Hardware InterruptsHardware Interrupts
IRQsIRQs
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IRQsIRQs (2 of 6)(2 of 6)
An interrupt is basically w hat it sounds like An interrupt is basically w hat it sounds like ² ² aa
message from one part of the computer tomessage from one part of the computer to
another (normally to the system processor) thatanother (normally to the system processor) that
tells it that it needs to stop w hat it is doing, andtells it that it needs to stop w hat it is doing, and
do something else instead.do something else instead.
W e use our computers in a way that requires the W e use our computers in a way that requires the
processor to at leastprocessor to at least appear appear to do many things atto do many things atonce.once.
Example: Editing a document w hilst listening toExample: Editing a document w hilst listening to
music.music.
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IRQsIRQs (3 of 6)(3 of 6)
The processor is able to do this by sharing its The processor is able to do this by sharing its
time among the various programs it is running time among the various programs it is running
and the different devices that need its attention.and the different devices that need its attention.
It seems as if its doing many things at onceIt seems as if its doing many things at once
because it is able to switch between tasks in abecause it is able to switch between tasks in a
blindingly hig h speed.blindingly hig h speed.
Many of the different parts of the PC need toMany of the different parts of the PC need to
send information to and from the CPU.send information to and from the CPU.
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IRQsIRQs (4 of 6)(4 of 6)
There are 2 basic ways that the processor could There are 2 basic ways that the processor could
use in order to give the different parts theuse in order to give the different parts the
attention they need:attention they need:
Polling Polling
Interrupting Interrupting
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IRQsIRQs (5 of 6)(5 of 6)
PollingPolling
Processor takes turns going to each device andProcessor takes turns going to each device andasking if they have anything they need it to do.asking if they have anything they need it to do.
W aste of cycles because the processor could be W aste of cycles because the processor could bedoing something useful instead.doing something useful instead.
Different devices need the processor·s attention atDifferent devices need the processor·s attention at
differing rates; the mouse needs attention far lessdiffering rates; the mouse needs attention far lessfrequently than the hard disk.frequently than the hard disk.
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IRQsIRQs (6 of 6)(6 of 6)
InterruptingInterrupting
Different devices request attention from the CPUDifferent devices request attention from the CPU w hen it is needed. w hen it is needed.
When a device has data to transfer, it generates an When a device has data to transfer, it generates aninterrupt saying ´I need your attention nowµ.interrupt saying ´I need your attention nowµ.
The processor stops w hat it is doing and deals with The processor stops w hat it is doing and deals with
the device that made the request for attention.the device that made the request for attention. It can actually handle many such requests at any oneIt can actually handle many such requests at any one
time. This is done using a priority level.time. This is done using a priority level.
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Interrupt ControllersInterrupt Controllers (1 of 3)(1 of 3)
Device interrupts are fed to the processor using Device interrupts are fed to the processor using
a special piece of hardware called ana special piece of hardware called an interruptinterrupt
controllercontroller..
The standard device for this is the Intel 8259 The standard device for this is the Intel 8259
interrupt controller. Nowadays, moderninterrupt controller. Nowadays, modern
motherboards incorporate this in the chipset.motherboards incorporate this in the chipset.
The controller passes the request on to the The controller passes the request on to the
CPU, telling it w hich devices issued the request.CPU, telling it w hich devices issued the request.
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Interrupt ControllersInterrupt Controllers (2 of 3)(2 of 3)
The original PC had 8 input lines connected to The original PC had 8 input lines connected to
the controller, and took requests from one of the controller, and took requests from one of
eig ht different devices. (IRQ 0 to 7)eig ht different devices. (IRQ 0 to 7)
Starting with IBM AT, a second interruptStarting with IBM AT, a second interrupt
controller was added to the system to expand it.controller was added to the system to expand it.
2 interrupts were2 interrupts were c as c aded c as c aded together in order nottogether in order not
to change the single interrupt line going to theto change the single interrupt line going to the
processor.processor.
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Interrupt ControllersInterrupt Controllers (3 of 3)(3 of 3)
The first interrupt controller still has 8 inputs and The first interrupt controller still has 8 inputs and
a single output going to the processor.a single output going to the processor.
Th
e second oneh
as th
e same design, but it takes Th
e second oneh
as th
e same design, but it takes8 new inputs (doubling the number of interrupts)8 new inputs (doubling the number of interrupts)
and its output feeds into input line 2 of the firstand its output feeds into input line 2 of the first
controller.controller.
If any of the inputs on the second controllerIf any of the inputs on the second controller
become active, the output from the controllerbecome active, the output from the controller
triggers interrupt #2 on the first controller, w hich triggers interrupt #2 on the first controller, w hich
then signals the processor.then signals the processor.
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NonNon--Maskable Interrupts (NMI)Maskable Interrupts (NMI) (1 of 2)(1 of 2)
All of the regular interrupts that we normally use All of the regular interrupts that we normally use
and refer to by number are calledand refer to by number are called m askable m askable
interrupts.interrupts.
The processor is able to mask (or temporarily The processor is able to mask (or temporarily
ignore) any interrupt if it needs to, in order toignore) any interrupt if it needs to, in order to
finish something else that it is doing.finish something else that it is doing.
On the other hand, the PC has an NMI that canOn the other hand, the PC has an NMI that can
be used for serious. conditions that demand thebe used for serious. conditions that demand the
processor·s immediate attention.processor·s immediate attention.
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NonNon--Maskable Interrupts (NMI)Maskable Interrupts (NMI) (2 of 2)(2 of 2)
The NMI cannot be ignored by the system unless The NMI cannot be ignored by the system unless
it is specifically shut off.it is specifically shut off.
When an NMI signal is received, t
he processor
When an NMI signal is received, t
he processorimmediately drops w hatever it was doing andimmediately drops w hatever it was doing and
attends to it.attends to it.
This could cause havoc. This is w hy it is used This could cause havoc. This is w hy it is used
only for critical problem situations, such asonly for critical problem situations, such as
serious hardware errors.serious hardware errors.
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Interrupt ConflictsInterrupt Conflicts
In general, interrupts are singleIn general, interrupts are single--device resources.device resources.
If you attempt to use two devices with the sameIf you attempt to use two devices with the same
IRQ, an IRQ conflict will result.IRQ, an IRQ conflict will result. It is possible to share an IRQ among more thanIt is possible to share an IRQ among more than
one device, but only under limited conditions.one device, but only under limited conditions.
If youh
ave two devices th
at you seldom use, youIf youh
ave two devices th
at you seldom use, youmay be able to have them share an IRQ.may be able to have them share an IRQ.
Common examples include COM port conflictsCommon examples include COM port conflicts
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Summary of IRQsSummary of IRQs (1 of 3)(1 of 3)
The table below provides summary information The table below provides summary information
about the 16 IRQ levels in a typical PC:about the 16 IRQ levels in a typical PC:
IRQIRQ BusBusLine?Line?
PriorityPriority T ypical T ypicalDefault UseDefault Use
Other Common UsesOther Common Uses
00 NoNo 11 System TimerSystem Timer NoneNone
11 NoNo 22 KeyboardKeyboard
ControllerController
NoneNone
22 NoNo
(rerouted)(rerouted)
n/an/a None: Cascade forNone: Cascade for
IRQs 8IRQs 8--1515
Modems, Very old ( EG A)Modems, Very old ( EG A)
Graphics Cards, COM3, COM4Graphics Cards, COM3, COM4
33 8/168/16--bitbit 1111 COM2 (secondCOM2 (second
serial port)serial port)
COM4, modems, sound,COM4, modems, sound,
network & tape accelerator cardsnetwork & tape accelerator cards
44 8/168/16--bitbit 1212 COM1 (first serialCOM1 (first serial
port)port)
COM3, modems, sound,COM3, modems, sound,
network & tape accelerator cardsnetwork & tape accelerator cards
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Summary of IRQsSummary of IRQs (2 of 3)(2 of 3)
IRQIRQ BusBus
Line?Line?
PriorityPriority T ypical T ypical
Default UseDefault Use
Other Common UsesOther Common Uses
55 8/168/16--bitbit 1313 Sound CardSound Card LPT2, LPT3, COM3, COM4,LPT2, LPT3, COM3, COM4,
modems, network and tapemodems, network and tape
accelerator cardsaccelerator cards
66 8/168/16--bitbit 1414 Floppy Disk Floppy Disk
ControllerController
Tape accelerator cards Tape accelerator cards
77 8/168/16--bitbit 1515 LPT1(first parallelLPT1(first parallel
port)port)
LPT2, LPT3, COM3, COM4,LPT2, LPT3, COM3, COM4,
modems, network and tapemodems, network and tape
accelerator cardsaccelerator cards
88 NoNo 33 RealReal--time Clock time Clock NoneNone
99 1616--bit only bit only 44 NoneNone Network or sound cards, SCSINetwork or sound cards, SCSI
host adapters, PCI devices,host adapters, PCI devices,
rerouted IRQ2 devicesrerouted IRQ2 devices
1010 1616--bit only bit only 55 NoneNone Network or sound cards, SCSINetwork or sound cards, SCSI
host adapters, PCI deviceshost adapters, PCI devices
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Summary of IRQsSummary of IRQs (3 of 3)(3 of 3)
IRQIRQ BusBus
Line?Line?
PriorityPriority T ypical T ypical
Default UseDefault Use
Other Common UsesOther Common Uses
1111 1616--bit only bit only 66 NoneNone Network or sound cards, SCSINetwork or sound cards, SCSI
host adapters, V G A video cards,host adapters, V G A video cards,
PCI devicesPCI devices
1212 1616--bit only bit only 77 PS/2 MousePS/2 Mouse Network or sound cards, SCSINetwork or sound cards, SCSI
host adapters, V G A video cards,host adapters, V G A video cards,
PCI devicesPCI devices
1313 NoNo 88 Floating PointFloating Point
Unit CoUnit Co--processorprocessor
NoneNone
1414 1616--bit only bit only 99 Primary IDE Primary IDE
channelchannel
SCSI host adaptersSCSI host adapters
1515 1616--bit only bit only 1010 Secondary IDE Secondary IDE
channelchannel
Network cards, SCSI hostNetwork cards, SCSI host
adaptersadapters