Chapter 9: Input/Output The Architecture of Computer Hardware and Systems Software: An Information Technology Approach 3rd Edition, Irv Englander John Wiley and Sons  2003 Wilson Wong, Bentley College Linda Senne, Bentley College

Chapter 9 Input / Output 9-2 Basic Model  Processing speed or program execution  determined primarily by ability of I/O operations to stay ahead of processor. Input Process Output

Chapter 9 Input / Output 9-3 I/O Considerations Speed Issues  CPU operates at speeds much faster than the fastest I/O device  Devices operate at different speeds  Bursts of data  Block data transfer required for some devices Coordination  Several devices perform I/O simultaneously  Unexpected input  Various input formats  Status information needed for each device

Chapter 9 Input / Output 9-4 I/O Device Interface Issues  Different formats  parallel interface  serial interface  Buffering of data  Burst vs. stream  Different control requirements  electromechanical

Chapter 9 Input / Output 9-5 Examples of I/O Devices

Chapter 9 Input / Output 9-6 Simple I/O Configuration

Chapter 9 Input / Output 9-7 I/O Modules Functions  Recognizes messages from device(s) addressed to it and accepts commands from the CPU  Provides a buffer where the data from memory can be held until it can be transferred to the disk  Provides the necessary registers and controls to perform a direct memory transfer  Physically controls the device  Copies data from its buffer to the device/from the CPU to its buffer  Notifies with interrupts

Chapter 9 Input / Output 9-8 Input/Output Modules  Programmed I/O  CPU controlled I/O  Interrupt Driven I/O  External input controls  Direct Memory Access Controllers  Method for transferring data between main memory and a device that bypasses the CPU

Chapter 9 Input / Output 9-9 Programmed I/O  I/O data and address registers in CPU  One word transfers  Address information for each I/O device  LMC I/O capability for 100 devices  Full instruction fetch/execute cycle  Primary use:  keyboards  communication with I/O modules (see DMA)

Chapter 9 Input / Output 9-10 Programmed I/O

Chapter 9 Input / Output 9-11 Programmed I/O Example

Chapter 9 Input / Output 9-12 Programmed I/O Example

Chapter 9 Input / Output 9-13 Interrupts  Signal that causes the CPU to alter its normal flow on instruction execution  frees CPU from waiting for events  provides control for external input  Examples  unexpected input  abnormal situation  illegal instructions  multitasking, multiprocessing

Chapter 9 Input / Output 9-14 The CPU - The Interrupt Cycle  Fetch / Execute cycle  Interrupt cycle HALT START Fetch Next Instruction Execute Instruction Check/Process Interrupt Interrupts Disabled

Chapter 9 Input / Output 9-15 Interrupt Terminology  Interrupt lines (hardware)  Interrupt request  Interrupt handlers  Program that services the interrupt  Also known as an interrupt routine  Process Control Block (PCB)  Located in a part of memory known as the stack area  All registers of a program are saved here before control is transferred to the interrupt handler

Chapter 9 Input / Output 9-16 Interrupt Terminology  Servicing the interrupt  suspends program in progress  saves pertinent information including last instruction executed and data values in registers in the PCB (process control block)  branches to interrupt handler

Chapter 9 Input / Output 9-17 Servicing an Interrupt

Chapter 9 Input / Output 9-18 Use of Interrupts  Notify that an external event has occurred  real-time or time-sensitive  Signal completion  printer ready or buffer full  Allocate CPU time  time sharing  Indicate abnormal event (CPU originates for notification and recovery)  illegal operation, hardware error  Software interrupts

Chapter 9 Input / Output 9-19 Multiple Interrupts  Identifying devices  Polling (checking for input in rotation)  Vectored interrupts (include address of interrupting device)  Interrupt priorities  Loss of data vs. task completion  Maskable (disabled) interrupts

Chapter 9 Input / Output 9-20 Vectored Interrupts

Chapter 9 Input / Output 9-21 Polled Interrupts

Chapter 9 Input / Output 9-22 Multiple Interrupts Example

Chapter 9 Input / Output 9-23 Direct Memory Access  Transferring large blocks of data  Direct transfer to and from memory  CPU not actively involved in transfer itself  Required conditions for DMA  The I/O interface and memory must be connected  The I/O module must be capable of reading and writing to memory  Conflicts between the CPU and the I/O module must be avoided

Chapter 9 Input / Output 9-24 DMA Instruction Set  Application program requests I/O service from operating system  privileged instructions  To initiate DMA, programmed I/O is used to send the following information: 1.location of data on I/O device 2.the starting location in memory 3.the size of the block 4.read/write  Interrupt to CPU upon completion

Chapter 9 Input / Output 9-25 DMA Initiation and Control

Chapter 9 Input / Output 9-26 Basic CPU-Memory-I/O Pathway*

Chapter 9 Input / Output 9-27 Bus Configuration

Chapter 9 Input / Output 9-28 Bus Characteristics  Data width in bits carried simultaneously  Throughput, i.e., data transfer rate in bits per second  Point-to-Point vs. Multipoint  Parallel vs. Serial  Use  Distance  Protocol

Chapter 9 Input / Output 9-29 Bus Hierarchy  Processor bus: on-chip  Cache bus (backside bus)  Memory bus (front-side bus)  connects the memory subsystem and processor  Local I/O bus  high-speed bus used to connect performance critical peripherals to memory and processor  Examples: PCI, VESA Local Bus  Standard I/O bus  connects slower peripherals (ISA) to Local I/O bus

Chapter 9 Input / Output 9-30 Wintel Bus Systems  ISA: Industry Standard Architecture  MCA: Micro Channel Architecture  EISA: Extended Industry Standard Architecture  Local Bus  PCI: Peripheral Component Interconnect (also Apple, Sun, Compaq Alpha Server)  VLB: VESA (Video Electronics Standards Association) Local Bus  AGP: Accelerated Graphics Port  Point-to-point channel from graphics controller to main memory  Co-exists with PCI

Chapter 9 Input / Output 9-31 Compaq 7000 and System Architecture

Chapter 9 Input / Output 9-32 External Interface Buses and Ports  Parallel port  Serial port  RS-232C and RS-422 buses  SCSI  Small Computer System Interface  USB, USB-2  Universal Serial Bus  IEEE 1394  Firewire  i.link

Chapter 9 Input / Output 9-33 SCSI Bus  ANSI standard but multiple variations  Really an I/O bus rather than simple interface  Supports multiple devices from a single SCSI port

Chapter 9 Input / Output 9-34 Root Hub USB  Multipoint bus  Hubs provide multiple connection points for I/O devices  Supports 127 devices Hub Topology Example

Chapter 9 Input / Output 9-35 USB and FireWire (IEEE 1394)  Both serial, multipoint bus specifications  Add/remove devices w/o powering down  Packet protocol for isochronous data transfer  Isochronous: delivery at regular time intervals  Guarantee specified throughput

Chapter 9 Input / Output 9-36 USB vs. FireWire  USB: slow to medium speed data transfer applications, i.e., storage devices  12 Mbits/sec  USB-2: high-speed data transfer  480Mbits/sec  FireWire: high-speed data transfer, i.e., full motion video with sound  400 Mbits/sec to 3.2 Gbits/sec

Chapter 9 Input / Output 9-37 Typical FireWire Configuration  Network-like characteristics  Device controllers independent

Chapter 9 Input / Output 9-38 Channel Architecture  Used in IBM mainframe computers  Channel subsystem  Separate I/O processor that serves as a CPU for I/O operations  Channel control words  Programs that transfer data between memory and an I/O device using DMA  Subchannels  Connected to a control unit module through one or more channel paths  Similar role to a device controller

Chapter 9 Input / Output 9-39 I/O Channel Architecture

Chapter 9 Input / Output 9-40 Copyright 2003 John Wiley & Sons All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the permissions Department, John Wiley & Songs, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein.”