UMass Amherst ECE 397A - I/O Systems (13 pages)

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I/O Systems



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I/O Systems

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Lecture Notes


Pages:
13
School:
University of Massachusetts Amherst
Course:
Ece 397a - Operating Systems

Unformatted text preview:

Chapter 12 I O Systems I O Hardware Application I O Interface Kernel I O Subsystem Transforming I O Requests to Hardware Operations I O Hardware Incredible variety of I O devices Common concepts Port typically status control data in data out Bus daisy chain or shared direct access Controller host adapter I O instructions control devices Devices have addresses used by Direct I O instructions Memory mapped I O 1 A Typical PC Bus Structure Device I O Port Locations on PCs partial 2 Device Functionality Progression Polling Determines state of device command ready busy Error Busy wait cycle to wait for I O from device It is a loop reading the status register over and over again A more efficient approach is through interrupts Let the host be notified by the device 3 Interrupts CPU Interrupt request line triggered by I O device Interrupt handler receives interrupts Maskable to ignore or delay some interrupts Can be turned off by CPU Interrupt vector contains the addresses of interrupt handlers to dispatch interrupt to correct handler Based on priority Some non maskable e g reserved for unrecoverable memory memory errors Interrupt mechanism also used for exceptions Interrupt Driven I O Cycle 4 Intel Pentium Processor Event Vector Table Direct Memory Access Used to avoid programmed I O for large data movement Requires DMA controller Bypasses CPU to transfer data directly between I O device and memory 5 Six Step Process to Perform DMA Transfer Application I O Interface I O system calls encapsulate device behaviors in generic classes Device driver layer hides differences among I O controllers from kernel Devices vary in many dimensions Character stream or block Sequential or random access Sharable or dedicated Speed of operation read write read only or write only 6 A Kernel I O Structure Characteristics of I O Devices 7 Block and Character Devices Block devices include disk drives Commands include read write seek Raw I O or file system access Memory mapped file access possible



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