Chapter 4Computer Organization

Vishal Shah

Vishal Pinto

Contents

• The Von Neumann Architecture• The Central Processing Unit• The Primary Memory• I/O devices• Interrupts• Conventional Contemporary Computers• Mobile Computers• Multiprocessors and Parallel Computers

Interrupts

Why Device Drivers?

read ( devID, myData, dataLength );

x = f ( myData, dataLength, …)

…// Start the device…while ((busy = = 1) || ( done = = 1)) wait( );//Device I/O complete…done = 0;

busy done

…while (( busy = = 0) && (done = = 1)) wait( );// Do the I/O operationbusy = 1;…

Software

Hardware

I/O Polling

A process in which a number of I/O devices are interrogated, one at a time, to determine if service is required.

Introduces Busy-wait situation.

. . . Device DeviceDevice

. . .

CPU

InterruptRequest flag

Detecting an Interrupt

Fetch-Execute cycle with an Interrupt

while (haltFlag not set during execution) { IR = memory[PC]; PC = PC + 1; execute (IR); if ( InterruptRequest) { memory[0] = PC; PC = memory [1]; }}

Conceptually ,hardware connects all device-done flags to the interrupt request flag using inclusive-OR logic

The Interrupt handler

Interrupt_Handler {

SaveProcessorState( );

for ( i = 0; i<Number_of_devices; i++)

if (device[i].done = = 1) goto device_handle(i);

/* Something wrong if we get here

}

• Extension to detect interrupt more rapidly?

Interrupt vector.

• Race condition ?

Interrupt occurs while the Interrupt handler is in the midst of execution.

Solution: Avoid it.

Disabling Interrupts

If ( InterruptRequest && InterruptEnabled ) {

/* Interrupt current process */

disableInterrupts ( );

memory [0] = PC;

PC = memory[1];

}

Trap InstructionUsed by a process running in user mode that wants to perform an operation that requires privileged instructions

trap

S

Mode

1

2

3

User SupervisorTrusted Code

Von Neumann Architecture

Primary Memory Unit

Device Controller

Device

CUALU

Address Bus

Data Bus

CPU

Bootstrapping the Machine

CMOS

POST

BIOS

Boot Prog

Loader

OS

Power UP

ROM

RAM

Boot Device

Boot Loader Program

Fixed_LOC:// Bootstrap loader entry point

load R1, =0

load R2, =LENGTH_OF_TARGET

/*The next instruction is really more like a procedure call than a machine instruction. It copies a block from BOOT_DISK to BUFFER_ADDRESS.*/

read BOOT_DISK, BUFFER_ADDRESS

Loop: load R3, [BUFFER_ADDRESS, R1]

store R3,[FIXED_DEST, R1]

incr R1

bleq R1, R2, loop

br FIXED_DEST

Mobile Computers

Features:• Physically light and small• Severely constrained in the rate at which it can

consume power• O/P devices are small and usually is speaker• Does not contain a storage device• Has removable devices like CF cards, NIC..

System-on-chip Technology

Set of memory and device functions that is needed by the onboard processor on a single chip.

Power Management

• Notebook computers– Switch OFF LCD display– Power down Disks

• Mobile computers– Switch OFF or dim displays– Reducing the clock speed of processor

Multiprocessors and Parallel Computers

• Parallel instruction Execution

• Pipelined function unit

Function UnitOperand 1

Operand 2Result

Operand 1

Operand 2 Result

Array processors

ALU

ALU

ALU

ALU

ALUControl Unit

Control Unit

Conventional Architecture SIMD Architecture

Shared Memory Multiprocessors

• Processors are Interconnected with one another with primary memory using specialized hardware

• Popular among programmers tools used to develop s/w for single process could easily be used with the shared memory architecture

• Distinct from Von Neumann architecture but rely upon it.

Distributed memory Multiprocessors

• Collection of CPU’s with their memory interconnected using high-speed n/w– High speed LAN or High speed fiber optic n/w

• Do not support ordinary sequential Programming languages like Shared memory machines do

• Exchanges data as messages

Network of workstations

• PC’s interconnected with a network• Usually individual computers with autonomous

executing units with their own OS