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

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

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