Bus structures

Unit objectives: Describe the primary types of buses,

and define interrupt, IRQ, I/O address, DMA, and base memory address

Describe PCI and PCIe buses, and PCI and non-PCI video standards

Topic A

Topic A: Buses Topic B: The PCI bus

Buses

Communication pathway Defined by

– How many bits it transmits at one time– Signaling technique– Data transfer speed

Three types– Address– Data– Expansion (I/O)

continued

Buses, continued

Address and data buses enable: – Basic CPU operation – Interactions with memory

Expansion bus– Communication pathway for non-core

components to interact with the CPU, memory, and other core components

– Adapter cards add functionality– PCIe is taking over from PCI– Older buses: ISA, EISA, Micro Channel,

and PC bus

PCI bus slots

The riser bus

Brings the basic wiring and control of a function to a motherboard

Decreases cost Two main riser standards:

– Audio/Modem Riser (AMR) – Communications and Networking Riser

(CNR)

Activity A-1

Examining buses

System interaction

Gain the attention of the CPU Access shared memory locations Extend the system BIOS Transfer data across the bus

Interrupts

Signal CPU that attention is needed– CPU stops what it was doing– Services the device request– Returns to its previous task

IRQs

Numerical identifiers Help CPU identify interrupt source Enforce priority of interrupts Common IRQs

– IRQ 1: Keyboard– IRQ2: Cascade IRQs 8-15– IRQ4: COM1– IRQ6: Floppy– IRQ12: PS/2 mouse– IRQ14: Primary IDE hard drive

Device Manager: IRQs

Activity A-2

Examining IRQ assignments

I/O addresses

Identify devices Have a range of numerical addresses

for each device Allow CPU to communicate multiple

commands Use 16-bit hexadecimal numbers User or BIOS configures the number

ranges

Device Manager: I/O addresses

Activity A-3

Viewing your computer’s I/O address assignments

DMA channels

DMA controller relieves CPU Dedicated channels Largely replaced by other techniques,

such as bus mastering

Activity A-4

Viewing your computer’sDMA channel assignments

Memory addresses

Devices extend system BIOS with new routines– Display adapters– SCSI controllers– IDE controllers

System BIOS locates and loads BIOS extensions using mapped memory location

Historically in upper memory block (UMB) – space between 640KB (0x000A0000) and 1MB

Device Manager: Base memory

Activity A-5

Viewing your computer’s memory address assignments

Topic B

Topic A: Buses Topic B: The PCI bus

PCI bus

32- or 64-bit bus– Pentium PCs

33 or 66 MHz clock speed 133-533 MBps maximum data transfer rate Up to 8 functions on a single card Up to 5 cards/slots per system Requires PnP

PCI adapter

PCIe

Newer standard Uses serial communication Lanes

– 2.5 Gbps in each direction using 8b/10b encoding (0.25 GBps)

– x1 (by one), x2, x4, x8, x12, x16, and x32 bus widths

Links – bidirectional switched lanes Can up-plug (e.g., x1 card in x16 slot) Can’t down-plug (not officially)

Multifunction cards

PCI spec supports multifunction cards Up to 8 functions per card Five slots/cards per system Total of 40 expansion devices

Activity B-1

Identifying a PCI bus

Video adapters

Generates signals sent to monitor Graphical interfaces involve massive

amounts of graphics data Can be built into motherboard or

adapter card Three types of video slots

– PCI– PCIe– AGP

PCI-based video

Low-end systems: video adapter built into motherboard

PCI is slowest of three types Share bus with all other PCI-based

devices Work well for two-monitor system

PCIe-based video

Designed to replace AGP cards x16 PCIe card has 4 GBps bandwidth

– Bidirectional nature allows up to 8 GBps

Simultaneous data movement upstream and downstream

Ideal for multimedia applications, such as gaming, photography, and videography

See http://tinyurl.com/ylpk4lw for comparison among PCI standards

A PCIe video card

AGP video adapters

Technically a port, not a bus Provides direct connection between video

adapter and CPU Referred to as #X Original performance benefit was accessing

and using main system memory– Direct Memory Execute (DIME)

Modern AGP cards use onboard memory, except in laptops

Multiple-monitor support Being phased out for PCIe

AGP adapter

Note the hook

AGP characteristics

32-bit bus Multiple of 33 MHz clock speed Speed “pumped” to as much as 533

MHz 266-2133 MBps data transfer rate PnP configurable

AGP slots

Typically brown; sometimes maroon or other dark color

Separated from other bus slots to help cooling

High-end systems include multiple, independent AGP slots

Activity B-2

Identifying graphics connections

Unit summary

Described the primary types of buses, and defined interrupt, IRQ, I/O address, DMA, and base memory address

Described PCI and PCIe buses, and PCI and non-PCI video standards