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ITFN 2601 Introduction to Operating Systems

ITFN 2601 Introduction to Operating Systems. Lecture 19 Input/Output Device Drivers. Agenda. I/O Hardware Memory-Mapped & DMA I/O Software Principles Programmed, Interrupt-based, & DMA I/O Device Drivers Device Independent I/O. I/O Hardware. Block devices

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ITFN 2601 Introduction to Operating Systems

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  1. ITFN 2601Introduction to Operating Systems Lecture 19 Input/OutputDevice Drivers

  2. Agenda • I/O Hardware • Memory-Mapped & DMA • I/O Software Principles • Programmed, Interrupt-based, & DMA I/O • Device Drivers • Device Independent I/O

  3. I/O Hardware • Block devices • Stores info in fixed-size blocks • Each independent & has own address • Ex. Drives • Character Devices • Stream-based • Ex. Printers, NICs, & mice

  4. Various Data Rates

  5. Device Controllers • Controls the device • Establishes a standard (IDE, SCSI, etc.) • Sits between the bus & device

  6. Memory-Mapped I/O • CPU writes to registers on the controller • CPU can also write to data buffer on controller (ex. video RAM) • Memory chunk in main RAM assigned to corresponding space on controller • Write to memory chunk : this writes to controller • Must be able to selectively disable cache!

  7. “Listening In On” Memory-Mapped I/O All I/O controllerslisten on main bus Multi-bus systems requiresnooping or address filtering

  8. DMA (Direct Memory Access) • Without DMA • WithDMA

  9. I/O Software Principles • Device Independence • Uniform Naming • Error Handling • Synch vs. Asynch transfers • Buffering • Dedicated vs. Sharable resource/device

  10. Programmed I/O Disadvantage – ties up CPU

  11. Interrupt-Driven I/O • Sending multiple blocks/chunks of data to device • Why not do something while device processes request • Let the device generate an interrupt when request complete – then resume with next block/chunk • Downside – too many interrupts!

  12. DMA-based I/O • Let DMA handle the I/O transaction • Reduces need for interrupts • Downsides: • DMA controller is slower than CPU • CPU might be idle anyway 

  13. Device Drivers • Code that provides an API to controller • Allows OS to access controller’s registers, memory buffer, etc. • Must conform to OS standard for block or character devices

  14. Device Driver Location

  15. Device Independent I/O • Uniform Interface for Drivers • OS to communicate w/out “hacking OS” each time a device is added

  16. Device Independent I/O • Buffering • Allow device to read/write data w/out having to flood process w/ interrupts

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