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OverviewIn this chapter you will learn how to:

Identify the structure and function of the expansion bus

Identify the modern expansion bus slotExplain classic system resources.

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Introduction

A slot located inside a computer (on the motherboard).

Allows additional boards to be connected to it.

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Introduction Three points to make a card work successfully

in an expansion slot:

1- Physical connectionPhysical connection: : expansion cards need to be built specifically for the expansion slots (require creation of industry standards)

2- CommunicationCommunication:: the card need some way to communicate with CPU (to receive instructions and send data)

3- DriversDrivers: operating system needs some means of enabling users to control the new device

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Structure and function of Exp. BusEvery device in the computer whether

soldered to the motherboard or snapped into the sockets or slot are connected to the external data bus and address bus.

Chipset provides extensionextension of address and data buses to the expansion slots, and thus to any expansion cards in those slots.

Bus connect between chipset and slots are called expansion busexpansion bus

What is system bus?

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Structure and function of Exp. BusExpansion slot connects to either

Northbridge or Southbridge depending on motherboard.

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Structure and function of Exp. BusMany systems have

more than one type of expansion Bus, with slots of one type connecting to Northbridge and slots of another connecting to Southbridge.

AGP slot is always connects to Northbridge.

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Expansion Bus speedAll devices solderedsoldered to the motherboard run

at the speed of the system crystal (system clock).

Ex. a motherboard with a 133-Mhz has at least a 133-Mhz Northbridge chip and at least a 133-Mhz Southbridge.

This doesn’t work for expansion cards: Cards also must be pushed by clock signal from a

crystal. If using system crystal need to make cards for every possible motherboard speed 8

Expansion Bus speedIBM had to make an extension to the external

data bus to run at it’s own standardized speed You can use this part of external data bus to

snap new devices into PC.

IBM achieved this goal by adding a different crystal, called expansion bus crystal.

No matter how fast the motherboard runs, the expansion slots run at a standard speed.

Expansion bus crystal controls the part of external data bus connected to expansion slots.

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All devices soldered to the motherboard run at the speed of the motherboard e.g. 133 Mhz (System crystal)

Expansion card run at standard speed. (Expansion crystal)

Expansion Bus speedExpansion slots run at a much lower speed

than frontside bus. The chipset acts as the divider between the two buses, compensating for the speed difference with: wait states and special buffering areas.

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PC Bus (XT Bus) On first generation IBM PCs

With 8088 processor with speed of 4.77 MHz8-bit wide of external data bus7-Mhz speed (of expansion bus)Manual configuration. What does it means?What does it means?

In this time expansion bus is faster than CPU speed.

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PC Bus (XT Bus)

AT BusWhen Intel invented 286 processor, IBM

created a new expansion bus that took advantage of 286’s 16-bit external data bus, yet also supported 8-bit cards.

IBM achieved this by simply adding a set of connections to the end of PC busCalled AT bus Ran at 7 MhzA 16-bit wide Manual configuration

8 bit cards could be used in the new 16 bit slots

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AT Bus

XT Bus orPC Bus

AT Bus

Industry Standard Architecture((ISA

Combining knowledge of PC and AT buses leads to creation of a book of standards called the IIndustry SStandard AArchitecture, or ISA first-generation expansion slots

If a company wanted to build a new kind of adaptor (card) for the PC, they simply followed the specifications in the ISA standard.

ISA bus:16-bit wide 7 Mhz speed Manual configuration

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Modern expansion busA better bus to solve problems of old expansion

bus was needed Narrow (Only 16 bits wide)Slow (Running at only about 7 MHz) Manually configured by move tiny jumpers (Time

consuming)It must be backward compatible. What doest means?What doest means?

Several designs to solve the above problems appeared: Micro Channel Architecture (MCA), Extended ISA (EISA), and Video Electronics Standards Association’s VESA, Local Bus (VL-Bus).

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Modern expansion busThey each had shortcoming that made them

less than optimal less than optimal replacements for ISA.Ex. MCA, EISA was expensive to make.

By 1993, the PC world was eager for a big name to come forward with a fast, wide, easy-to-configure, and cheap new expansion bus (PCI Bus)

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PCI BusMade by Intel.PCI (PPeripheral CComponent IInterconnect) bus.It provided a wider, faster, more flexible

alternative than any previous expansion bus.It could coexist with other expansion buses

(ex. ISA) to enable users to keep their old ISA cards and slowly migrate to PCI

It had a powerful burst modemode feature that enabled very efficient data transfers32-bit wide 33-Mhz speedSelf-configuring (plug and play - PnP)

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PCI slot PCI card

PCI and ISA

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PCI bus expansion slot are shorter than ISA slot and offset farther from the edge of the system board

Accelerated Graphics Port (AGP)An AGP slot is a PCI slot but one with a direct

connection to the Northbridge. A specialized video-only version of PCI.

Don’t try to snap a sound card or modem card in to it.

Usually one AGP in Motherboard. Why?Brown color.

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Accelerated Graphics Port (AGP)

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PCI-X A huge enhancement to current PCI

fully backward compatible (h/w, S/w). 64-bit wide bus. much enhanced speed.

Its slots will accept regular PCI cards.PCI-X 2.0: 44 speed grades (measured in MHz)

PCI-X 66, PCI-X 133, PCI-X 266, and PCI-X 533 .Its candidate for workstationworkstation and serversservers

because they have the “need for speedneed for speed” and the need for “backward compatibilitybackward compatibility”.

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PCI-X and PCI

PCI-X

PCI

Mini PCIMini-PCI is used for laptops

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PCI Express (PCI-E)

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PCI-E is the latest and the fastest expansion bus, and most popular expansion bus used today.A PCIe device has its own direct connection to the

Northbridge, so it does not wait for other device.PCIe uses a point-to-point serial connection

instead of shared parallel communication used by PCI.

A PCIe connection uses oneone wire for sending and oneone for receiving (instead of using one wire instead of using one wire for each bit in PCI parallel communicationfor each bit in PCI parallel communication).

Each of these pairs of wires between a PCIe controller and a device is called a LaneLane

Each lane allows a maximum transfer rate of 2.5 Gbps Gbps in each direction.

PCI Express PCI-EPCI Express bus can be built by combining

several lanes on order to achieve higher performance .

PCI Express can use 1,2,4,8,12,16 and 32 lanes. to achieve max. bandwidth of 160 Gbps160 Gbps

Most common is 16-lane (x 16) version used for video cards

Other version of PCIe are general purpose (x4).

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PCI Express PCI-E

PCI Express x2 busPCI-E with two lanes.Highly scalable because bandwidth can be

increased by increasing the number of lanes.

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PCI-E Slots

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The PCI Express bus defines a different type of slot based on the number of lanes in the system.

Why Serial Communication? Almost all PC buses PC buses (ISA, EISA, PCI, AGP) use

parallel communication.Parallel transmits several bits several bits at a time and serial

only one bitone bit at a time. For example in a PCI which is parallel 32 bit communication 32 wires carry one bit of data.

Serial communication requires two wires ( one to transmit and another to receive data).

Serial communication allows operations at much higher clock speeds than in parallel because in parallel communication problems with propagation delay appear most frequently .

Parallel communication is half duplex while serial is full duplex. 32

Full and Half duplexA half-duplex system provides for communication in both

directions, but only one direction at a time (not simultaneously).

Full duplex means, connection that allows communication in two directions simultaneously at once.

Example: PCI Express can use 1,2,4,8,12,16 and 32 lanes. to achieve

max. bandwidth of 160 Gbps160 Gbps Max bandwidth= (32lanes X 2.5GB)X 2 (Ful duplex)=160

GBPS.

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System resourcesYou can divide communication with CPU into 4 aspects

called system resourceSystem resource are:

1. I/O addressI/O address: how CPU sends commands to devices2.2. IRQIRQ: how devices tell CPU they need communication3.3. DMADMA: how CPU enables devices to talk directlydirectly to RAM4.4. MemoryMemory: how CPU talks to RAM on devices

Not all devices use all 4 resources: all use #1, most use #2, few use #3 or #4.

New devices must have their system resource configuration.

System resources are now automated

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I/O AddressAll devices connect to the address and data

buses.Every device in the computer needs an I/O I/O

addressaddress.Is different patterns used by the CPU to talk to the

devices inside the computer.All devices respond to unique patterns of ones

and zeros built into them. Most PCs have 65,535 different I/O addresses

(16 bits for I/O address 2^16). I/O addresses are shown in hexadecimal format

from 0000 to FFFF.36

Hexadecimal and BinaryRepresenting tenten in binary and hex

Binary 1 0 1 0 (1 eight and 1 two)Hexadecimal Ah (pronounced “A hex”)

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1

8

22 21 20

0 1 0

1010 Binary Hexadecimal Table

0 0 0 0 01 0 0 0 12 0 0 1 03 0 0 1 14 0 1 0 0 5 0 1 0 1 6 0 1 1 07 0 1 1 1

8 1 0 0 09 1 0 0 1A 1 0 1 0B 1 0 1 1C 1 1 0 0 D 1 1 0 1 E 1 1 1 0F 1 1 1 1

4 2 1

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I/O Address1. If CPU wants to send I/O address it put the

expansion bus into I/O mode through (IO/MEM) wire.

2. When bus goes into I/O mode, all device on bus look for patterns of one and zeroes to appear on the address bus.

Rules of I/O AddressesAll devices must have an I/O addressAll devices respond to more than one pattern

(I/O address is a range of patterns)- at least four discrete address.The first value of a range are generally refereed

to as base address.Once a device is using an I/O address no other

device can use it (not-shared) Most I/O addresses were set up by standard IBM.

(Example?Example?) Or can be set at boot by operating system (OS).Exercise: how do you know I/O addresses

for devices of your computer.39

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Interrupt Requests

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CPU can communicatecommunicate and talktalk to all device in computer using:I/O Address busBIOS

But how device tell CPU its need attentions:Interrupt request Interrupt request

used by devices to get the CPU’s attention

•IRQ0 = System Timer

•IRQ1 = Keyboard Controller

Interrupt Requests

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Every CPU has an INT (interrupt) wire.

If device puts voltage on this wire. The CPU will:Stop what it is doing and deal with the

interrupting device.This will be fine if the PC had only one device But PCs have many device and all of them need

to interrupt the CPU.Therefore PC needs some kind of “traffic coptraffic cop”.

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This Traffic cop called IOAPIC

This Traffic cop called IOAPIC

Interrupt and IOAPIC chip

IOAPICIOAPIC chip (I/O Advanced Programmable Interrupt Controller) chip was hooked to the INT wire and had special interrupt wiress called IRQs that run to all devices on the expansion bus.

IRQ (Interrupt ReQuest)Note: IOAPIC functions are usually built into

Southbridge.Each device that needs to interrupt the CPU

activate its IRQ line. IOAPIC then interrupts CPUCPU queries IOAPIC to know the device and

begins communication with it over the address bus.

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IRQ No two devices could share IRQsPIC is the previous generation to IOAPIC.PIC system use fewer IRQs.

PIC had 16 IRQ lines where as IOAPIC has 24 IRQs lines.Which IRQ controller do you have in your system?

Some IRQs are not assigned to device we call them “Open IRQs”.

Plug and Play assigns IRQs to new devices as needed

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COM and LPT PortsIBM created standardstandard preset combinations of

IRQs and I/O addresses for serial and parallel ports.

COM port for serial device connections and LPT for parallel device connections.COM terms came from communicationLPT came from line printer

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COM and LPT PortsLack of available IRQs in early system lead

IBM to double up the IRQ for serial devices.ExceptionException of rule that NO two device could

share IRQ.Combination of I/O address and IRQs:

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Ports I/O base address IRQCOM1 03F8 IRQ4COM2 02F8 IRQ3COM3 03E8 IRQ4COM4 02E8 IRQ3LPT1 0378 IRQ7LPT2 0278 IRQ5

Direct Memory Access (DMA)

Direct Memory Access (DMA) is the process of Accessing memory directly without involving the CPU in time CPU does internal calculation and address and data bus are available.

It enables the system to run background applications without interrupting the CPU. Example?Example?

ProblemsProblems:More than one device wants to use DMA.CPU suddenly need to use the bus system will

another device use it.

DMA: Direct Memory Access8237 chip (or DMA controllerDMA controller) controls all DMA

functions. It assigns numbers called DMA channels DMA channels to enable

devices to request use of DMA. AMD controller also handles the data passes from

I/O devices to RAM and vice versa.

DMA chip sends data along the external data bus whenthe CPU is busy with internal calculation and not using the external data bus.

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Direct Memory Access (DMA)

DMA Map

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DMA: Direct Memory Access DMA type:

Classic DMA.Ultra DMA.

Classic DMA Classic DMA is dying as it is very slow and only supports 16-bit data transfers. On most systems, only floppy drivesfloppy drives still use classic DMA. All systems still support classic DMA

Ultra DMAUltra DMA Most devices today that use DMA do so without

going through DMA controller. These devices known as bus mastersbus masters

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Bus Mastering devicesThey have circuitry that enables them to

watch for other devices accessing the external data bus; they can detect a potential conflict and get out of the way on their own.

They ignore DMA controller, and do not have DMA channels Popular in hard drives and totally automatic

and invisible.High speed data transfers, popular in EIDE

hard drives.

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Bus Mastering devicesBus-mastering capabilities are much more

efficient than DMA.Neither PCI nor PCIe support DMA. So you So you

will never find DMA device that snaps into will never find DMA device that snaps into these expansion busthese expansion bus.

Any device that want to use DMA must do so through onboard connection.

ExerciseExercise: identify DMA channels in your system

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Memory addressesSome expansion cards need memory

addresses.Two reasons:

1. a card may have onboard RAM that CPU needs to address.

2. a few cards come with an onboard ROM, called adapter or option ROM.

The RAM or ROM must steal memory addresses away from the main system RAM to enable CPU to access RAM or ROM

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