No interleaving Single interleaving Double interleaving 12 IO Software Goals of

No interleaving single interleaving double

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No interleaving Single interleaving Double interleaving 12 I/O Software Goals of I/O Software Structured I/O Software » Interrupt Handlers » Device Drivers » Device-Independent I/O SW » User-Space I/O SW
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13 Goals of I/O Software Device independence » Read and Write from Floppy, Disk, CD-ROM without modifying programs Uniform naming » Names are not dependent on the specific device Different devices of same type have similar name » In UNIX, all I/O is integrated with the file system Error handling done as close to HW as possible » Propagate errors up only when lower layer cannot handle it. » Hide errors as much as possible—many HW errors are transient Synchronous read/write at application level » Most I/O hardware operates asynchronously » Synchronous (blocking) read/write easier to program 14 Structured I/O SW to meet Goals Structured I/O SW to meet these Goals Interrupt Handlers Device Drivers Device-Independent OS SW User-level Software
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15 Interrupt Handlers Hidden from applications Used to bridge gap between asynchronous I/O hardware and synchronous read/write semantics Often implemented as top-half and bottom-half handlers » Top-half does as little as possible not scheduled » Bottom-half closely related to (if not exactly) the device driver scheduled 16 Device Drivers Device dependent code Each device driver handles (at most) one class of devices Device drivers communicate with the device controllers » Only part that knows the details of the device.
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