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Buses in a Graphics Context:

Buses in a Graphics Context:. PCI vs. AGP. Context: Why use a specialized bus?. Given: I/O takes a significant amount of time, esp. Graphics I/O. If Graphics I/O moves into separate bus, system buses freed up for other devices.

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Buses in a Graphics Context:

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  1. Buses in a Graphics Context: PCI vs. AGP

  2. Context: Why use a specialized bus? • Given: I/O takes a significant amount of time, esp. Graphics I/O. • If Graphics I/O moves into separate bus, system buses freed up for other devices. • Why use a specialized graphics bus (e.g. AGP) over a universal bus (e.g. PCI)?

  3. Features: What is a Bus? • A way of connecting multiple devices together so that data can be transferred between them • Shared by multiple devices --> Only 1 device can send at any particular time • Has multiple lines each transferring a single bit. # of lines known as bus width • Different types of lines: control, address, and data • Multiplexed • Buses can be synchronous or asynchronous

  4. PCI • Intro • Created in 1992 - replaced ISA. • Solved many technical issues of ISA bus • IRQ • Address conflicts (jumpers) • Features Plug-and-Play technology • Because of high speed data transfer only 3-4 devices can be plugged into one PCI bus, as opposed to 6-7 on ISA board. • Two PCI buses can be connected with PCI-to-PCI bridges • These bridges divide into primary and secondary bridges and are physically isolated.

  5. PCI (cont’d)

  6. PCI (cont’d) • Technical Attributes • PCI supports up to 64 bit data transfer and 133MHz clock which allows for transfer of 1066 megabytes per second. • Features direct memory access (DMA) • Bus arbitration: Fair, Round Robin, Master Capable • Several pins on the bus are selected to implement bus mastering • any device can take over the control of the bus at any time • if possible, one device may occupy the whole bandwidth

  7. PCI (cont’d) • Interrupts: • Interrupts are not synchronized with other signals on the bus, since they can be activated and used at any time. • PCI design does not specify how interrupts are to be shared – this is resolved by motherboard manufacturers.

  8. AGP

  9. AGP (cont’d) • Higher throughput, both peak and sustained • Transferring data on rising and falling edges of clock ticks • Uses demultiplexed data and address lines • Sideband addressing allows pipelining (i.e. Sending requests while receiving data • High peak throughput of 533 MB/s on 32 data lines

  10. AGP (cont’d) • Memory access improvements • Direct Memory Execution (DIME) • Uses system memory as own, using GART • Allows concurrent system memory usage • Saves money on expensive graphics memory • Useful for on-board graphics

  11. PCI Address/data multiplexed Non-pipelined Peak at 133MB in 32 bits Multi-target, single master Connects to multiple peripherals besides memory I/O AGP Address/data de-multiplexed Pipelined requests Peak at 533MB/s in 32 bits Single target, single master - makes DIME possible Memory read/write only, no other I/O operations Comparison

  12. Comparisons (cont’d) • Data Transfers • AGP makes multiple requests for data during a bus or memory access. • PCI makes one request, and does not make another until the data it request has been transferred. • AGP does not replace the PCI bus, but it is a dedicated connection that can used only by the graphics subsystem

  13. Conclusions • AGP is faster • PCI is more flexible

  14. Bibliography • AGP Information: • chart@hyperlink.net.au. PCI Information. http://home.hyperlink.net.au/~chart/program.htm#agp (Feb. 2003). • Intel Corporation. Accelerated Graphics Port Technology Home. http://www.intel.com/technology/agp/ (Feb. 2003). • General Bus Information: • Kozierok, Charles M. The PC Guide. http://www.pcguide.com/ (Feb 2003). • Stallings, William. Computer Organization and Architecture: Designing for Performance. 5th ed. New Jersey: Prentice Hall, 2000. • PCI Information: • Adaptec, Inc. Adaptec: A Fundamental Element of the PCI Architecture is the Concept of Bridges. http://www.adaptec.com/worldwide/support/supporteditorial.html?sess=no&language=English+US&prodkey=PCI_bridge_whitepaper (Feb. 2003). • Apple Computer, Inc. PCI Bus Overview1. http://developer.apple.com/techpubs/hardware/DeviceManagers/pci_srvcs/pci_cards_drivers/PCI_BOOK.5.html (Feb. 2003). • Quatech, Inc. PCI Bus Overview. http://www.quatech.com/Application_Objects/FAQs/comm-over-pci.htm (Feb 2003). • Sundance Multiprocessor Technology Ltd. & Sundance Italia S.r.l & Sundance DSP Inc., E&OE. A brief description of the PCI Bus. http://www.sundance.com/edge/files/pci.htm (Feb. 2003).

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