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 Three types How many bits it transmits at one time Signaling technique Data transfer speed Three types Address Data Expansion (I/O) continued 3

Buses, continued Address and data buses enable: Expansion bus 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 4

PCI bus slots 5

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 8

Interrupts Signal CPU that attention is needed CPU stops what it was doing Services the device request Returns to its previous task 9

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 10

Device Manager: IRQs 11

Examining IRQ assignments 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 13

Device Manager: I/O addresses 14

Viewing your computer’s I/O address assignments 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 16

Viewing your computer’s DMA channel assignments Activity A-4 Viewing your computer’s DMA 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 18

Device Manager: Base memory 19

Viewing your computer’s memory address assignments 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 33 or 66 MHz clock speed 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 22

PCI adapter 23

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 31

AGP adapter Note the hook 32

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

Identifying graphics connections 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