ee488_IO_2 - N orthwestern P olytechnic U niversity EE488...

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Unformatted text preview: N orthwestern P olytechnic U niversity EE488 Lecture Notes Input/Output (System Bus) What is a bus? EE488 - NPU Like a highway that many people (components) can use. The highway (bus) can only support two users at any time. (1 master and 1 slave, more on this later) The bus is physically a bunch of wires . The wires are a collection of Data signals Address signals Control signals A Bus is EE488 - NPU A shared communication link. A common set of wires used to connect Multiple subsystems. Buses are typically named for the function they provide. (i.e. memory bus, I/O bus, local bus, IDE bus...) Registers Registers ALU Bus controller Bus controller Memory Memory disk disk modem modem printer printer Memory bus I/O bus CPU Internal CPU buses Bus Types EE488 - NPU Computers have several types of busses (1) General purpose I/O bus- I.e. PCI Bus- lots of different types of devices use this bus.- Cost effective.- Performance is a compromise- 32-bit, 33MHz = 133MB/s (2) Special High-Speed busses- I.e. AGP (Advanced Graphics Port)- Only Typically only one device can connect- Optimized for high performance- 32-bit, 66MHz = 266MB/s (3) Low cost Serial busses - I.e. USB bus- Cost effective bus adding low speed devices * printers, scanners, mice, etc- Serial bus = 1.5MB/s System Buses Overview EE488 - NPU South Bridge North Bridge Whats inside the north bridge chip? Whats inside the south bridge chip? Theres even more... not shown due to space Modern Computer System EE488 - NPU Advantages of Buses EE488 - NPU System bus Versatility (expandability): New devices can be easily added. Peripherals can be moved between computer systems that use the same bus standards. Significant Cost Benefits : A single set of wires can be shared in multiple ways. Common standards allow many people to design peripherals that can work in the bus. CPU CPU memory memory I/O device I/O device I/O device I/O device I/O device I/O device Disadvantages of Buses EE488 - NPU System bus Creates communication Bottleneck : The bandwidth of the bus can limit the maximum I/O throughput. Busses are designed to meet the needs of many, thus, sacrifice performance for flexibility. Maximum Bus Speed is Largely Limited by Length of bus number of devices on the bus Need to support a wide range of devices with- varying latencies.- varying data transfer rates. CPU CPU memory memory I/O device I/O device I/O device I/O device I/O device I/O device A Closer Look at a Bus EE488 - NPU (Local Bus) (System Bus) CPU CPU bridge bridge A A B B C C D D E E address address control data data control 0030h 0040h 0050h 0010h 0020h Busses typically composed of 3-different functions......
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ee488_IO_2 - N orthwestern P olytechnic U niversity EE488...

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