Chapter 7Input/Output

Kristian NaessQicai Guo

Roy TorresMark Bacchus

Yue KunAlberto Chestaro

External Devices

The three key elements to a computer are: • Processor(CPU), memory, and I/O devices

I/O devices are called peripherals. Peripherals can be classified as:• Human Readable, Machine Readable, and Communication.

Input devices. Examples: mouse, keyboard, joystick, scanners, microphone, ect. Output devices. Examples: monitors, speakers, printer, ect.

I/O Modules

Peripherals are connected through I/O modules. Data transfers significantly slower than memory and processor.

Generic Model of I/O Module Basic and major function of a

module:• Control and Timing• Processor

Communication• Device Communication• Data Buffering• Error Detection

Device Communcation

Three type of signals:• Control Signal• Data Signal• Status Signal

Generic Model of I/O Module Basic and major function of a

module:• Control and Timing• Processor

Communication• Device Communication• Data Buffering• Error Detection

Intel 82C55A I/O module

Operations

Three types of I/O operations:• Interrupt• Non-Interrupt• Programmed

ATA Device

What is the problem with programmed I/O ?Delays

Any solutions to this problem ?

Issue an I/O command do some useful work

Interrupt Driven I/O

Why are interrupts useful ? • External analogy to exceptions • Allow response to unusual external events without inline

overhead (polling)

Idea: Use interrupts to reduce polling overhear for Input/output • Processor initiates I/O operations• Device interrupts processor when its ready• Interrupt handler transfers data into memory• Control returned to currently executing program

Using Interrupts for Input/Output

Interrupt Processing Hardware Software

Device controller or other system

hardware issue an interrupt

Processor finishes execution of

current instruction

Processor signals acknowledgment

of interrupt

Processor pushes PSW and PC onto

control stack

Processor loads new PC value

based on interrupt

Save remainder of process state information

Process interrupt

Restore process state information

Restore old PSW and PC

How does the processor determines which device issued the interrupt ?

Design Issues

• The most straightforward approach

• Impractical to use • Multiple I/O

modules attached

Multiple interrupt

lines

• Time Consuming • Poll each I/O

module to determine which module caused the interrupt

Software Poll

• More efficient• It provides a

hardware poll Daisy Chain

• Must gain control of the bus before it can raise the interrupt requested line

• In responds on the interrupt acknowledge line

Bus arbitration

Advantages

Reduced vs. interrupt cost polling time

Improved program modularity (no more polling code)

Preserves the ability of old programs to run in new configurations

Complications

Additional hardware required (interrupt controller, etc)

How to deal with several devices ?

What if more than one interrupt occurs at one ?

Advantage & Complications

Processor sets up I/O operation, continues its work Device performs I/O (a long time) Device completes, interrupts the processor Processor responds to interrupt, transfers the data I/O is complete. => Interrupts save overhead of polling.

Interrupt-Driven I/O (Overview)

P MemI/O I/O

Memory Bus

I/O Bus

82C59A InterruptController

Direct Memory Access (DMA)

Drawbacks of Interrupt I/O

What is DMA???

Programming DMA Transfers

Major Components (Registers) of a DMA Controller

What Type of Devices Use DMA

DMA and Multi-Core Processors

Downside Of DMA

The External Interface: Firewired and Infiniband

There are two major characteristics of interface:• Parallel Interface- which involves multiple lines to

transfer data• Serial Interface- which only has one line to transmit

data

Types of Interface

Parallel• Multiple bits are

transferred simultaneously, just as all of the bits of a word are transferred simultaneously over the data bus

• Traditionally been used for higher-speed peripherals

Serial• Bits must be transmitted

one at a time• Traditionally been used

for printers and terminals• new generation of high-

speed serial interfaces, are making parallel interfaces much less common.

Types of Interface

Types of Interface

• Point-to-Point interface provides a dedicated line between the I/O module and the external device.

• Multipoint interfaces are in effect external buses and they exhibit the same type of logic as the buses

Point-to-Point & Multipoint Configuration

• There has been great interest in developing a high-speed alternative to Small Computer System Interface (SCSI) and other small-system I/O interfaces. The result is the IEEE standard 1394,for a High Performance Serial Bus, commonly known as FireWire.

• It is very high speed, low cost, and easy to implement.• One of the strengths of the FireWire interface is that it uses serial

transmission (bit at a time) rather than parallel.

FireWire Serial Bus

• Uses a daisy-chain configuration (Tree-structure)• up to 63 devices connected off a single port• up to 1022 FireWire buses can be interconnected

using bridges, enabling a system to support as many peripherals as required.

• Provides hot plugging• Provides Automatic configuration

FireWire Configuration

FireWire Configuration

FireWire Configuration

The three layers (Stacks) Physical Layer- Defines the transmission media that are

permissible under FireWire and the electrical and signaling characteristics of each

Link Layer-Describes the transmission of data in the packets

Transaction Layer-Defines a request–response protocol that hides the lower-layer details of FireWire from applications

Stacks

Physical• specifies several alternative transmission media and their connectors,

with different physical and data transmission properties• converts binary data into electrical signals for various physical media• provides the arbitration service that guarantees that only one device at a

time will transmit data• Contains logic that allows all the attached devices to configure themselves

so that one node is designated as the root of the tree and other nodes are organized in a parent/child relationship forming the tree topology

Stacks

LinkTwo types of transmission are supported:• Asynchronous: A variable amount of data and several

bytes of transaction layer information are transferred as a packet to an explicit address and an acknowledgment is returned.

• Isochronous: A variable amount of data is transferred in a sequence of fixed-size packets transmitted at regular intervals

Stacks

• Is a recent I/O specification aimed at the high-end server market

• Not necessary to have the basic I/O interface hardware inside the server chassis

• net- working, and connections between servers are accomplished by attaching all devices to a central fabric of switches and links

• Unlike PCI, InfiniBand’s channel design enables I/O devices to be placed up to 17 meters away from the server using copper, up to 300m using multimode optical fiber, and up to 10 km with single-mode optical fiber

InfiniBand Architecture

InfiniBand uses virtual lanes

InfiniBand Operation

• Physical: Specification defines three link speeds (1X,4X, and 12X) giving transmission rates of 2.5, 10, and 30Gbps, respectively. The physical layer also defines the physical media, including copper and optical fiber.

• Link: Defines the basic packet structure used to exchange data, including an addressing scheme that assigns a unique link address to every device in a subnet. It also, includes the logic for setting up virtual lanes and for switching data through switches from source to destination within a subnet.

• Network: Routes packets between different InfiniBand subnets.• Transport: Provides reliability mechanism for end-to-end

transfer of packets across one or more subnets.

InfiniBand Operation

InfiniBand Operation