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Input/Output

Input/Output. 5.1 Principles of I/O hardware 5.2 Principles of I/O software 5.3 I/O software layers 5.4 Disks 5.5 Clocks 5.6 Character-oriented terminals 5.7 Graphical user interfaces 5.8 Network terminals 5.9 Power management. Chapter 5. Principles of I/O Hardware. Geschwindigkeit

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Input/Output

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  1. Input/Output 5.1 Principles of I/O hardware 5.2 Principles of I/O software 5.3 I/O software layers 5.4 Disks 5.5 Clocks 5.6 Character-oriented terminals 5.7 Graphical user interfaces 5.8 Network terminals 5.9 Power management Chapter 5

  2. Principles of I/O Hardware Geschwindigkeit Some typical device, network, and data base data rates

  3. Device Controllers • I/O devices have components: • mechanical component • electronic component • The electronic component is the device controller • may be able to handle multiple devices • Controller's tasks • convert serial bit stream to block of bytes • perform error correction as necessary • make available to main memory

  4. E/A-Befehle A] Spezielle Ein/Ausgabe-Befehle, die spezielle Ein/Ausgangsports des Prozessors ansprechen: • E/A-Vorgang definieren, Gerätestatus setzen • E/A-Vorgang anstoßen • Ende des Vorgangs erkennen, Gerätestatus lesen B] Memory-Mapped I/O:Arbeitsspeicher-Adressbereiche werden für die E/A reserviert • Speicherzugriffe mit diesen Adressen sind Zugriffe auf einen I/O-Controller

  5. Memory-Mapped I/O (1) • Separate I/O and memory space • Memory-mapped I/O • Hybrid

  6. I/O, Memory, and Data Transfer (a) A single-bus architecture (b) A dual-bus memory architecture

  7. Principles of I/O SoftwareGoals of I/O Software • Device independence • programs can access any I/O device • without specifying device in advance • (floppy, hard drive, or CD-ROM) • Uniform naming • name of a file or device a string or an integer • not depending on which machine • Error handling • handle as close to the hardware as possible

  8. Further Aspects of I/O Software • Synchronous vs. asynchronous transfers • blocked transfers vs. interrupt-driven • Buffering • data coming off a device cannot be stored in final destination • Sharable vs. dedicated devices • disks are sharable • tape drives would not be

  9. E/A-Verfahren Schneller Prozessor  langsames E/A-Gerät • Prozessor-gesteuert“Langer” E/A-Befehl oder aktive Warteschleife:Ausführung dauert solange, bis Gerät mit Abwicklung fertig ist) • Interrupt-gesteuerte E/AProzessor tauscht Daten mit Controller aus und stößt E/A an. Controller führt E/A durch und signalisiert danach Prozessor per Interrupt • Direct Memory Access (DMA)Prozessor stößt Block-E/A an. Controller tauscht Daten mit Arbeitsspeicher in eigener Regie aus. Interrupt an Prozessor bei Blockende.

  10. Programmed I/O (1) Steps in printing a string

  11. Programmed I/O (2) Writing a string to the printer using programmed I/O

  12. Interrupts How interrupts happens. (Connections between devices and interrupt controller actually use interrupt lines on the bus rather than dedicated wires) Bus

  13. Interrupt-gesteuerte E/A Programm: versorge Controller starte E/A blockiere Controller: führe E/A mit Gerät durch gebe Interrupt Gerät: bedrucke Papier FortsetzungnachInterrupt: Lese Controller Status Auftragsendebehandlung Interrupt-routine: quittiere Interrupt Setze Programm fort Hardware / Peripherie Systemsoftware / Prozessor

  14. Interrupt-Driven I/O Writing a string to the printer using interrupt-driven I/O • Code executed when print system call is made • Interrupt service procedure

  15. Direct Memory Access (DMA) Operation of a DMA transfer

  16. I/O Using DMA Printing a string using DMA • code executed when the print system call is made • interrupt service procedure

  17. I/O Software Layers Layers of the I/O Software System

  18. Interrupt Handlers (1) Interrupt handlers are best hidden • have driver starting an I/O operation block until interrupt notifies of completion Interrupt procedure does its task • then unblocks driver that started it Steps must be performed in software after interrupt completed • Save regs not already saved by interrupt hardware • Set up context for interrupt service procedure

  19. Interrupt Handlers (2) • Set up stack for interrupt service procedure • Ack interrupt controller, reenable interrupts • Copy registers from where saved • Run service procedure • Set up MMU context for process to run next • Load new process' registers • Start running the new process

  20. Device Drivers • Logical position of device drivers is shown here • Communications between drivers and device controllers goes over the bus

  21. Device-Independent I/O Software (1) Functions of the device-independent I/O software

  22. Device-Independent I/O Software (2) (a) Without a standard driver interface (b) With a standard driver interface

  23. Device-Independent I/O Software (3) (a) Unbuffered input (b) Buffering in user space (c) Buffering in the kernel followed by copying to user space (d) Double buffering in the kernel

  24. Device-Independent I/O Software (4) Networking may involve many copies

  25. User-Space I/O Software Layers of the I/O system and the main functions of each layer

  26. Plattenspeicher

  27. Plattenspeicher • Sektor • Spur / Track • Zylinder • Oberfläche / Kopf • Cluster

  28. Disks Disk parameters for the original IBM PC floppy disk and a Western Digital WD 18300 hard disk

  29. RAID - Systeme RAID:Redundant Array of Independent (or Inexpensive) Disks • Geschwindigkeit:Gestreute Speicherung • Zuverlässigkeit: Redundante Speicherung RAID Levels: 0: Gestreute Speicherung 1: Redundante Speicherung 2: Gestreute Speicherung und Fehlerkorrektur 3: Gestreute Speicherung und verbesserte Fehlerkorrektur

  30. RAID Strip / Stripe:Teilfolge von Sektoren • Raid levels 0 through 2 • Backup and parity drives are shaded paralleles Lesen Sicherungskopien und paralleles Lesen Fehlerkorrektur

  31. RAID • Raid levels 3 through 5 • Backup and parity drives are shaded

  32. CD Hardware (1) Recording structure of a CD or CD-ROM

  33. CD Hardware (2) Logical data layout on a CD-ROM

  34. CD Hardware (3) • Cross section of a CD-R disk and laser • not to scale • Silver CD-ROM has similar structure • without dye layer • with pitted aluminum layer instead of gold

  35. Disk Formatting (1) A disk sector

  36. Disk Formatting (2) An illustration of cylinder skew

  37. Disk Formatting (3) • No interleaving • Single interleaving • Double interleaving

  38. Disk Arm Scheduling Algorithms (1) • Time required to read or write a disk block determined by 3 factors • Seek time • Rotational delay • Actual transfer time • Seek time dominates • Error checking is done by controllers

  39. Disk Arm Scheduling Algorithms (2) Pending requests Initial position Shortest Seek First (SSF) disk scheduling algorithm

  40. Disk Arm Scheduling Algorithms (3) The elevator algorithm for scheduling disk requests

  41. Error Handling • A disk track with a bad sector • Substituting a spare for the bad sector • Shifting all the sectors to bypass the bad one

  42. Stable Storage(by means of mirror disk) Analysis of the influence of crashes on stable writes

  43. ClocksClock Hardware Üblich sind 2 Arten von Zeitgeber-Funktionen: • Uhr • Uhr stellen • Uhr lesen • Selbsttätige Zeit- und Datumsfortschaltung • Wecker (Timer) • Wecker stellen • Wecker läuft selbsttätig • Wecker erzeugt Interrupt

  44. ClocksClock Hardware A programmable clock (Wecker-Funktion) 00000 ....... 5499 5500 5496 00001 5498 00002 5497 Alarm: Zeit abgelaufen 5500

  45. Clock Software (2) Simulating multiple timers with a single clock • Zeitauftragsliste (sortiert nach Zeit) • jeweils Wecker passend zum vorderstenAuftrag stellen

  46. Soft Timers • A second clock available for timer interrupts • specified by applications • no problems if interrupt frequency is low • Soft timers avoid interrupts • kernel checks for soft timer expiration before it exits to user mode • how well this works depends on rate of kernel entries

  47. Character Oriented TerminalsRS-232 Terminal Hardware • An RS-232 terminal communicates with computer 1 bit at a time • Called a serial line – bits go out in series, 1 bit at a time • Windows uses COM1 and COM2 ports, first to serial lines • Computer and terminal are completely independent

  48. Character Oriented TerminalsRS-232 Terminal Hardware

  49. RS-232 Terminal Hardware Bitserielle Übertragung, zeichenweise asynchron: • 1-2 Startbits (Aktivieren und Einsynchronisieren des Empfängers) • 7 Datenbits • 1 Parity Bit • 1-2 Stopbits (garantierte Pause bis zum nächsten Zeichen) start start 1 2 3 4 5 6 7 9 stop

  50. Input Software (1) • Central buffer pool • Dedicated buffer for each terminal

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