Input - • Assembles block of bytes in a buffer •...

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Input /Output Devices
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1/31/12 2 Devices Devices Storage devices (disk, tapes) Transmission devices (network card, modem) Human interface devices (screen, keyboard, mouse) Specialized device (joystick)
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Device-Computer/Device-Device Communication Physically: via signals over a cable or through the air Logically: via a connection point - port (e.g., Serial port, USB port) Multiple devices are connected via a bus A common set of wires and a rigidly defined protocol that specifies a set of messages that can be sent on the wires
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1/31/12 4 Device I/O Controller I/O units typically consist of Mechanical component (device itself) Electronic component (device controller/adapter, e.g., circuit board). Example : Disk controller Implements the disk side of the protocol that does: bad error mapping, prefetching, buffering, caching Converts the serial bit stream, coming off the drive into a block of bytes, Performs error correction
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Unformatted text preview: • Assembles block of bytes in a buffer • Verifies checksum • Copies error-free block to main memory. • Controller components 1/31/12 5 I/O Ports • 4 registers - status, control, data-in, data-out – Status- states whether the current command is completed, byte is available, device has an error, etc – Control- host determines to start a command or change the mode of a device – Data-in- host reads to get input – Data-out- host writes to send output 1/31/12 6 Interrupt-Driven I/O (Host-controller interface) • CPU hardware has the interrupt report line that the CPU senses after executing every instruction – Device raises an interrupt – CPU catches the interrupt and saves the state (e.g., Instruction pointer) – CPU dispatches the interrupt handler – Interrupt handler determines cause, services the device and clears the interrupt • Why interrupts?...
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This note was uploaded on 01/30/2012 for the course CS 354 taught by Professor Staff during the Fall '08 term at Purdue.

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Input - • Assembles block of bytes in a buffer •...

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