Computers

Internal Communication

Basic Computer System

MAIN MEMORY

ALU CNTL.....

BUS

CONTROLLER

Processor

I/O moduleInterconnections

BUS

Memory

Local and Peripheral

Bus

Bus Operation

Transfer Quantity (word)Address busControl busData bus

SpeedClock speed

Controller

PROCESSOR REGISTER

REGISTER

REGISTER

BUFFER

Controller Operation

PROCESSOR REGISTER

REGISTER

REGISTER

BUFFER

VALUE

VALUE

VALUE

PROCESSOR

BUFFERHEADER CRC

PROCESSOR

BUFFERBUFFERBUFFERBUFFERBUFFERBUFFERBUFFERBUFFERBUFFERBUFFERBUFFERBUFFER

CRC

CPU passes parameters into the registersController transfers data into the card bufferCard processor checks the CRC Data is transferred from the buffer to the bus

I/O Operations

For the I/O device to communicate with the CPU, the designer includes additional registers in the CPU.

•I/O Address Register contains address of I/O device•I/O Buffer Register contains the value to be transferred to/from the I/O device

I/O Registers

IR

300 PC

CONTROL ARITHMETIC-LOGIC

ACCUM

PROGRAM

1940

5941

2941

300

301

302

DATA

0003

0002

940

941

I/O Address

I/O Buffer

I/O Processing

Programmed I/OControlTestRead/Write

Interrupt Driven I/ODirect Memory Access

1. Programmed I/O

Issue an I/O request

CPU is tied up checking the I/O device until the response is ready.

Solution: Interrupt Processing

Wait until I/O finished

Continue program

2. Interrupt Processing

Issue an I/O requestStore program parametersStart another processProcess interruptReturn to original process

3. DMA

Processor issues a request, thenGoes about its businessDMA module transfers the data, thenTells the processor

Programmed I/O

Issue an I/O request

CPU is tied up checking the I/O device until the response is ready.

Solution: Interrupt Processing

Wait until I/O finished

Continue program

Interrupt Processing

Interrupt Processing

Interrupt Processing

Start FETCH EXECUTE

Halt

CHECKINTERRUPT

Interrupt Processing

Issue an I/O requestStore program parametersStart another processProcess interruptReturn to original process

Classes of Interrupts

Program: illegal program operations

Timer: scheduled special operationsI/O: device controller signals completion of operations or errorHardware Failure: power failure, memory parity error, etc.

Interrupt Request (IRQ) Registers

IR

300 PC

CONTROL ARITHMETIC-LOGIC

ACCUM

PROGRAM

1940

5941

2941

300

301

302

DATA

0003

0002

940

941

I/O Address

I/O Buffer

IRQ

Stack Addr.

Interrupt Stack

Add a CPU register: stack pointer.Recognize interruptStore register contents (push stack)Process interruptRestore register contents (pop stack)

STACK

PROGRAM COUNTER

INSTRUCTION REGISTER

ACCUMULATOR

Etc.

Base Address

May also contain interim program values

Data Transfer:Interrupt Driven I/O

MAIN MEMORY

BUFFER

CPU

T AAD

CONTROLLER

DASD

CPUCPUCPUCPU

Data Transfer:Direct Memory Access

MAIN MEMORY

BUFFER

CPU

T AAD

DASD

CONTROLLERCONTROLLERCONTROLLERCONTROLLERCONTROLLER