1 / 28

Chapter 13: I/O Systems

Chapter 13: I/O Systems. Chapter 13: I/O Systems. I/O Hardware Application I/O Interface Kernel I/O Subsystem Transforming I/O Requests to Hardware Operations. Objectives. Explore the structure of an operating system’s I/O subsystem

kateb
Download Presentation

Chapter 13: I/O Systems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 13: I/O Systems

  2. Chapter 13: I/O Systems • I/O Hardware • Application I/O Interface • Kernel I/O Subsystem • Transforming I/O Requests to Hardware Operations

  3. Objectives • Explore the structure of an operating system’s I/O subsystem • Discuss the principles of I/O hardware and its complexity

  4. Overview • The control of devices connected to the computer is a major concern of operating-system designers. • I/O devices vary so widely in their function and speed, varied methods are needed to control them. • Two conflicting trends of I/O-device technology: • Increasing standardization of software and hardware interfaces • An increasingly broad variety of I/O devices. • To encapsulate the details and oddities of different devices, the kernel of an operating system is structured to use device-driver modules • The device drivers present a uniform device-access interface to the I/O subsystem

  5. I/O Hardware • Incredible variety of I/O devices • Common concepts • Port: a connection point • Bus: a set of wires and a rigidly defined protocol that specifies a set of messages that can be sent on the wires • Controller: a collection of electronics that can operate a port, a bus, or a device. • I/O instructions control devices • The controller has one or more registers for data and control signals. The processor communicates with the controller by reading or writing bit patterns in these registers • How can the processor give commands and data to a controller to accomplish an I/O transfer? • Direct I/O instructions • Memory-mapped I/O

  6. A Typical PC Bus Structure

  7. Device I/O Port Locations on PCs (partial)

  8. Polling • Determines state of device • command-ready indicates command is available for the controller to execute • Busy indicates the device is busy working • Error indicates there is something wrong • Basic handshaking notion: • The host repeatedly reads the busy bit until it is clear • The host sets the writes bit in the command register and writes a byte into the data-out register • The host sets the command-ready bit • When the controller notices that the command-ready bit is set, it sets the busy bit • The controller reads the command register and sees the write command. It reads the data-out register to get the byte and does the I/O to the device. • The controller clears the command-ready bit, clears the error bit in the status register to indicate that the device I/O succeeded, and clears the busy bit to indicate that it is finished

  9. Interrupt-Driven I/O Cycle

  10. Interrupts • The hardware mechanism that enables a device to notify the CPU is called an interrupt • Interrupt handler receives interrupts • Most CPU has two Interrupt-request line triggered by I/O device: nonmaskable and maskable • Nonmaskable is reserved for event such as unrecoverable memory erros • Maskable to ignore or delay some interrupts

  11. 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

  12. A Kernel I/O Structure

  13. Characteristics of I/O Devices

  14. Block and Character Devices • Block devices include disk drives • Commands include read, write, seek • Raw I/O or file-system access for OS and database-management systems • Memory-mapped file access possible • Character devices include keyboards, mice, serial ports • Commands include get and put • Libraries layered on top allow line editing

  15. Network Devices • Varying enough from block and character to have own interface • Unix and Windows NT/9x/2000 include socket interface • Separates network protocol from network operation • Includes select functionality: returns information about which sockets have a packet waiting to be received and which sockets have room to accept a packet to be sent

  16. Clocks and Timers • Provide current time, elapsed time, timer to trigger a certain operation at time T • Programmable interval timer used for timings, periodic interrupts

  17. Blocking and Nonblocking I/O • Blocking - process suspended until I/O completed • Easy to use and understand • Insufficient for some needs • Nonblocking - I/O call returns as much as available • User interface, data copy (buffered I/O) • Implemented via multi-threading • Returns quickly with count of bytes read or written

  18. Two I/O Methods Synchronous Asynchronous

  19. Kernel I/O Subsystem • Scheduling • Some I/O request ordering via per-device queue: a waiting queue of request for each device • Some OSs try fairness: rearrange the order of the queue to improve the overall system efficiency and the average response time • Buffering - store data in memory while transferring between devices or between a device and an application • To cope with device speed mismatch • To cope with device transfer size mismatch • To maintain “copy semantics”: the version of the data written to disk is guaranteed to be the version at the time of the application system call, independent of any subsequent changes in the application’s buffer

  20. Device-status Table

  21. Sun Enterprise 6000 Device-Transfer Rates

  22. Kernel I/O Subsystem • Caching - fast memory holding copy of data • Always just a copy • Key to performance • Spooling - hold output for a device • If device can serve only one request at a time • i.e., Printing • Device reservation - provides exclusive access to a device • System calls for allocation and deallocation • Watch out for deadlock

  23. Error Handling • OS can recover from disk read, device unavailable, transient write failures • Most return an error number or code when I/O request fails • System error logs hold problem reports

  24. Kernel Data Structures • Kernel keeps state info for I/O components, including open file tables, network connections, character device state • Many, many complex data structures to track buffers, memory allocation, “dirty” blocks • Some use object-oriented methods and message passing to implement I/O

  25. UNIX I/O Kernel Structure

  26. I/O Requests to Hardware Operations • Consider reading a file from disk for a process: • Determine device holding file • Translate name to device representation • Physically read data from disk into buffer • Make data available to requesting process • Return control to process

  27. Life Cycle of An I/O Request

  28. End of Chapter 13

More Related