bus structures unit objectives: describe the primary types of buses, and define interrupt, irq, i/o...
TRANSCRIPT
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