1 / 50

TK 2123 COMPUTER ORGANISATION & ARCHITECTURE

TK 2123 COMPUTER ORGANISATION & ARCHITECTURE. Lecture 9: Input/output. Contents. This lecture will discuss: Computer Modules . Input Output Techniques Interrupts. Introduction.

richardsa
Download Presentation

TK 2123 COMPUTER ORGANISATION & ARCHITECTURE

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. TK 2123COMPUTER ORGANISATION & ARCHITECTURE Lecture 9: Input/output

  2. Contents • This lecture will discuss: • Computer Modules. • Input Output Techniques • Interrupts.

  3. Introduction • I/O operations take up a lot of computer time - much CPU time is wasted waiting for the completion of the I/O task. • Several different techniques are combined to resolve the problem of synchronising and handling I/O between a variety of different I/O devices operating with different quantities of data at different speeds.

  4. Connecting • All the units must be connected • Different type of connection for different type of unit • Memory • Input/Output • CPU

  5. Computer Modules

  6. Memory Connection • Receives and sends data • Receives addresses (of locations) • Receives control signals • Read • Write • Timing

  7. Input/Output Connection(1) • Similar to memory from computer’s viewpoint • Output • Receive data from computer • Send data to peripheral • Input • Receive data from peripheral • Send data to computer

  8. Input/Output Connection(2) • Receive control signals from computer • Send control signals to peripherals • e.g. spin disk • Receive addresses from computer • e.g. port number to identify peripheral • Send interrupt signals (control)

  9. CPU Connection • Reads instruction and data • Writes out data (after processing) • Sends control signals to other units • Receives (& acts on) interrupts

  10. Input/Output Problems • Wide variety of peripherals • Delivering different amounts of data • At different speeds • In different formats • All slower than CPU and RAM • Need I/O modules

  11. Input/Output Module • Interface to CPU and Memory • Interface to one or more peripherals

  12. Generic Model of I/O Module

  13. External Devices • Human readable • Screen, printer, keyboard • Machine readable • Monitoring and control • Communication • Modem • Network Interface Card (NIC)

  14. External Device Block Diagram

  15. I/O Module Function • Control & Timing • CPU Communication • Device Communication • Data Buffering • Error Detection

  16. I/O Steps • CPU checks I/O module device status • I/O module returns status • If ready, CPU requests data transfer • I/O module gets data from device • I/O module transfers data to CPU • Variations for output, DMA, etc.

  17. I/O Module Diagram

  18. I/O Module Decisions • Hide or reveal device properties to CPU • Support multiple or single device • Control device functions or leave for CPU

  19. Input Output Techniques • Programmed • Interrupt driven • Direct Memory Access (DMA)

  20. Three Techniques for Input of a Block of Data

  21. Programmed I/O • CPU has direct control over I/O • Sensing status • Read/write commands • Transferring data • CPU waits for I/O module to complete operation • Wastes CPU time

  22. Programmed I/O - detail • CPU requests I/O operation • I/O module performs operation • I/O module sets status bits • CPU checks status bits periodically - polling • I/O module does not inform CPU directly • I/O module does not interrupt CPU • CPU may wait or come back later

  23. I/O Commands • CPU issues address • Identifies module (& device if >1 per module) • CPU issues command • Control - telling module what to do • e.g. spin up disk • Test - check status • e.g. power? Error? • Read/Write • Module transfers data via buffer from/to device

  24. Addressing I/O Devices • Under programmed I/O data transfer is very like memory access (CPU viewpoint) • Each device given unique identifier • CPU commands contain identifier (address)

  25. I/O Mapping • Memory mapped I/O • Devices and memory share an address space • I/O looks just like memory read/write • No special commands for I/O • Large selection of memory access commands available • Isolated I/O • Separate address spaces • Need I/O or memory select lines • Special commands for I/O • Limited set

  26. Memory Mapped and Isolated I/O

  27. Interrupt Driven I/O • Overcomes CPU waiting • No repeated CPU checking of device • I/O module interrupts when ready

  28. Interrupts • Mechanism by which other modules (e.g. I/O) may interrupt normal sequence of processing • Allows to time share the CPU between several different programs at once. • Modern computers provide interrupt capability by providing special control lines to the central processor known as interrupt lines. • Program • e.g. overflow, division by zero • Timer • Generated by internal processor timer • Used in pre-emptive multi-tasking • I/O • from I/O controller • Hardware failure • e.g. memory parity error

  29. Interrupt Cycle • Added to instruction cycle • Processor checks for interrupt • Indicated by an interrupt signal • If no interrupt, fetch next instruction • If interrupt pending: • Suspend execution of current program • Save context • Set PC to start address of interrupt handler routine • Process interrupt • Restore context and continue interrupted program

  30. Transfer of Control via Interrupts

  31. Multiple Interrupts • Disable interrupts • Processor will ignore further interrupts whilst processing one interrupt • Interrupts remain pending and are checked after first interrupt has been processed • Interrupts handled in sequence as they occur • Define priorities • Low priority interrupts can be interrupted by higher priority interrupts • When higher priority interrupt has been processed, processor returns to previous interrupt

  32. Multiple Interrupts - Sequential

  33. Multiple Interrupts – Nested

  34. Interrupt Driven I/O: Basic Operation • CPU issues read command • I/O module gets data from peripheral whilst CPU does other work • I/O module interrupts CPU • CPU requests data • I/O module transfers data

  35. Simple Interrupt Processing

  36. CPU Viewpoint • Issue read command • Do other work • Check for interrupt at end of each instruction cycle • If interrupted:- • Save context (registers) • Process interrupt • Fetch data & store

  37. Changes in Memory and Registers for an Interrupt

  38. Design Issues • How do you identify the module issuing the interrupt? • How do you deal with multiple interrupts? • i.e. an interrupt handler being interrupted The interrupt handler (or interrupt service routine, ISR) - determines appropriate course of action. This process is known as servicing the interrupt.

  39. Identifying Interrupting Module (1) • Different line for each module • Limits number of devices • A vectored interrupt is used, in which the address of the interrupting device is included as part of the interrupt. • Faster, but requires additional hardware to implement. • Software poll • Use a general interrupt that is shared by all devices. • CPU asks each module in turn • Slow

  40. Vectored Interrupt vs Polled Interrupt Vectored Interrupt Polled Interrupt

  41. Identifying Interrupting Module (2) • Daisy Chain or Hardware poll • Interrupt Acknowledge sent down a chain • Module responsible places vector on bus • CPU uses vector to identify handler routine • Bus Master • Module must claim the bus before it can raise interrupt

  42. Multiple Interrupts • Each interrupt line has a priority • Higher priority lines can interrupt lower priority lines • If bus mastering, only current master can interrupt

  43. Direct Memory Access • Interrupt driven and programmed I/O require active CPU intervention • Transfer rate is limited • CPU is tied up • DMA is the answer. • DMA is more efficient for transferring large volumes of data.

  44. DMA Function • Additional Module (hardware) on bus • DMA controller takes over from CPU for I/O operations.

  45. Typical DMA Module Diagram

  46. DMA Operation • CPU tells DMA controller:- • Read/Write • Device address • Starting address of memory block for data • Amount of data to be transferred • CPU carries on with other work • DMA controller deals with transfer • DMA controller sends interrupt when finished

  47. DMA Transfer: Cycle Stealing • DMA controller takes over bus for a cycle • Transfer of one word of data • Not an interrupt • CPU does not switch context • CPU suspended just before it accesses bus • i.e. before an operand or data fetch or a data write • Slows down CPU but not as much as CPU doing transfer.

  48. Fly-By • While DMA using buses processor idle • Processor using bus, DMA idle • Known as fly-by DMA controller • Data does not pass through and is not stored in DMA chip • DMA only between I/O port and memory • Not between two I/O ports or two memory locations • Can do memory to memory via register

  49. I/O Channels • I/O devices getting more sophisticated • e.g. 3D graphics cards • CPU instructs I/O controller to do transfer • I/O controller does entire transfer • Improves speed • Takes load off CPU • Dedicated processor is faster

  50. Thank youQ & A

More Related