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

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 ConsiderationsSpeed 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/ProcessInterrupt

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 device2. the starting location in memory3. the size of the block4. 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 10000 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

Hub 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