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System software in UG, Essays (university) of System Programming

Madurai Kamaraj UniversitySystem Programming

system Programming note To Unit I

Typology: Essays (university)

2017/2018

Uploaded on 10/06/2018

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INTRODUCTION
What is system software?
•System software consists of a variety of programs that support the
operation of a computer.
•System programs were developed to make computers better adapted to
the needs of their users.
•It allows us to focus on application without knowing details of
machine.
•Examples of system software are text editor, compiler, loader or
linker, debugger, macro processor, operating system etc.
•Text editor is used to create and modify the program.
•Compiler translate the user program into machine
language
•Loaders are system programs that prepare machine
language programs for execution
•Debugger helps to detect errors in the program.
•A translator is used to translate the assembly code into
machine code. This translator is called an assembler.
The most important system software is the OS, which is an integrated
system of programs that manages the system resources, and provides various
support services such as the computer executing the application programs of
users
SYSTEM SOFTWARE AND MACHINE ARCHITECTURE
YSTEM SOFTWARE ( CS 2304) UNIT - I
LALITHAMBIGAI.B
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INTRODUCTION

What is system software?

  • System software consists of a variety of programs that support the

operation of a computer.

  • System programs were developed to make computers better adapted to

the needs of their users.

  • It allows us to focus on application without knowing details of

machine.

  • Examples of system software are text editor, compiler, loader or

linker, debugger, macro processor, operating system etc.

  • Text editor is used to create and modify the program.
  • Compiler translate the user program into machine

language

  • Loaders are system programs that prepare machine

language programs for execution

  • Debugger helps to detect errors in the program.
  • A translator is used to translate the assembly code into

machine code. This translator is called an assembler.

The most important system software is the OS, which is an integrated

system of programs that manages the system resources, and provides various

support services such as the computer executing the application programs of

users

SYSTEM SOFTWARE AND MACHINE ARCHITECTURE

System software is different from application software as follows.

APPLICATION SOFTWARE SYSTEMSOFTWARE

1. It concerns with solution of

some problem.

2. Its focus is on the application

not on the computing system.

It supports the operation and use of the

computer.

It is related to the architecture of the

machine on which they are to run.

(i.e.) Most of the system software is

machine dependent.

Machine dependency

We discuss how the system software dependent on machine

architecture.

Assembler – Assembler translates mnemonics instructions into

machine code. These mnemonics instructions involves different types of

instruction sets, instruction formats, addressing modes, etc. that varies from

one machine architecture to another. Hence the assembler design depends on

machine architecture.

Complier – It translates high level language code into machine code. It

involves the following 5-phases,

1. Lexical phase

2. syntactic analysis phase

3. Intermediate code generation phase

designed to illustrate the most commonly encountered hardware features and

concepts that are often found in real machines.

Versions of SIC

SIC comes in two versions.

1. The standard model.

2. an XE version (XE stands for “extra equipment” or “extra

expensively)

These two versions have been designed to be “upward compatible”,

means that an object program for the standard SIC machine will also execute

properly on a SIC / XE system. Such upward compatibility is often found on

real computers that are closely related to one another.

  • SIC Machine Architecture
  • SIC / XE Machine Architecture
  • SIC Programming Examples

SIC Machine Architecture

Memory

  • Memory consists of 8-bit bytes
  • 3 consecutive bytes form a word (24 bits)
  • All addresses of SIC are byte addresses
  • Words are addressed by the location of their lowest numbered byte.
  • There are total of 32,768 (2^15) bytes in the computer memory

Registers

  • There are five registers each is 24 bits in length.
  • The following table indicates the numbers, mnemonics and uses of

these registers

Mnemonics Number Special Use

A 0 Accumulator, used for

arithmetic operation

X 1 Index register, used for

addressing

L 2 Linkage register, the

Jump to Subroutine

(JSUB) instruction stores

the return address in this

register.

PC 8 Program Counter,

contains the address of

the next instruction to be

fetched for execution.

SW 9 Status word, contains a

variety of information,

including a condition

code (CC)

The numbering scheme has been chosen for compatibility with the XE

version of SIC. i.e., number 3 to 7 is used by SIC / XE.

Data formats

  • Integers are stored as 24-bit binary number
  • Negative values are represented as 2’s compliment representation.
  • Characters are stored using their 8-bit ASCII codes
  • There is no floating point hardware on the standard version of SIC.
  • Arithmetic instructions

ADD, SUB, MUL, DIV

(Ex) ADD WORD (Adds register A with memory WORD and result is

stored in A)

  • Comparison instruction

COMP

(ex) COMP WORD (Compares the value in register A with WORD and sets

condition code CC to indicate the result <, = or >)

  • Condition jump instruction

JLT, JEQ, JGT

These instructions can test the setting of CC and jump accordingly.

  • Subroutine linkage instruction

JSUB – jumps to the subroutine, placing the return address in

register L.

RSUB – returns by jumping to the address contained in

register L.

I nput and output

  • Input and output is performed by transferring 1 byte at a time or

from the rightmost of bits of register A.

  • Each device is assigned a unique 8-bit code.
  • There are three input / output instructions with device code as

operand namely TD, RD and WD.

  • TD – Test Device instruction sets whether the addressed device

is ready to send or receive a byte of data. CC is set for the

result.

  • A setting of < means that the device is ready to send or receive
  • (^) A setting = means that the device is not ready.
  • A program needing to transfer data must wait until the device is

ready then execute

Read Data (RD) or Write Data (WD)

  • This sequence should be continual for each byte of delta.

SIC / XE MACHINE ARCHITECTURE

  • Memory
  • Registers
  • Data formats
  • Instruction formats
  • Addressing modes
  • Input and output

Memory

The memory structure for SIC / XE is the same as SIC standard model

memory. The maximum memory on SIC / XE is1 MB (2^20 bytes). This

increase leads to change in instruction formats and addressing modes.

Registers

Mnemonics Number Special Use

A 0 Accumulator, used for arithmetic

operation

  • Format ( 2 bytes)
  • Format (3 bytes)
  • Format ( 4 bytes)

Format 1 (1 byte):

op {8}

Format 2 (2 bytes):

op {8} r1 {4} r2 {4}

Format 3 (3 bytes):

op {6} n i x b p e displacement {12}

Format 4 (4 bytes):

op {6} n i x b p e address {20}

Formats 3 & 4 introduce addressing mode flag bits:

n=0 & i=

Immediate addressing - TA is used as an operand value (no memory

reference)

n=1 & i=

Indirect addressing - word at TA (in memory) is fetched & used as an

address to fetch the operand from

n=0 & i=

Simple addressing TA is the location of the operand

n=1 & i=

Simple addressing same as n=0 & i=

Flag x:

x=1 Indexed addressing add contents of X register to TA calculation

Flag b & p (Format 3 only):

b=0 & p=

Direct addressing displacement/address field containsTA (Format 4

always uses direct addressing)

b=0 & p=

PC relative addressing - TA=(PC)+disp (-2048<=disp<=2047)*

b=1 & p=

Base relative addressing - TA=(B)+disp (0<=disp<=4095)**

* note - in PC relative, disp is interpreted as a 12 bit signed integer in 2's

complement

** note - in Base relative, disp is interpreted as a 12 bit unsigned integer

Flag e:

e=0 use Format 3

e=1 use Format 4

Input and Output (I/O):

  • 28 (256) I/O devices may be attached, each has its own unique 8-bit

address

  • 1 byte of data will be transferred to/from the rightmost 8 bits of

register A

Three I/O instructions are provided:

RD Read Data from I/O device into A

WD Write data to I/O device from A

TD Test Device determines if addressed I/O device is ready to send/receive

a byte of data. The CC (Condition Code) gets set with results from this test:

< device is ready to send/receive

= device isn't ready

SIC/XE Has capability for programmed I/O (I/O device may input/output

data while CPU does other work) - 3 additional instructions are provided:

SIO Start I/O

HIO Halt I/O

STR2 RESB 11

ZERO WORD 0

ELEVEN WORD 11

Input and Output operation Program

INLOOP TD INDEV : TEST INPUT DEVICE

JEQ INLOOP : LOOP UNTIL DEVICE IS

READY

RD INDEV : READ ONE BYTE INTO A

STCH DATA : STORE A TO DATA

OUTLP TD OUTDEV : TEST OUTPUT DEVICE

JEQ OUTLP : LOOP UNTIL DEVICE IS

READY

LDCH DATA : LOAD DATA INTO A

WD OUTDEV : WRITE A TO OUTPUT DEVICE

INDEV BYTE X ‘F5’ : INPUT DEVICE NUMBER

OUTDEV BYTE X ‘08’ : OUTPUT DEVICE NUMBER

DATA RESB 1 : ONE-BYTE VARIABLE

To transfer two hundred bytes of data from input device to

memory

LDX ZERO

CLOOP TD INDEV

JEQ CLOOP

RD INDEV

STCH RECORD, X

TIX B

JLT CLOOP

INDEV BYTE X ‘F5’

RECORD RESB 200

ZERO WORD 0

B200 WORD 200

Subroutine to transfer two hundred bytes of data from input

device to memory

JSUB READ

READ LDX ZERO

CLOOP TD INDEV

JEQ CLOOP

RD INDEV

STCH RECORD, X

TIX B200 : add 1 to index compare 200 (B200) JLT CLOOP RSUB …….. …….. INDEV BYTE X ‘F5’ RECORD RESB 200 ZERO WORD 0 B200 WORD 200

Example Programs (SIC/XE)

Simple data and character movement operation

LDA

STA ALPHA

LDA

STCH C.

ALPHA RESW 1

C1 RESB 1

Arithmetic operations

LDS INCR

LDA ALPHA

ADD S,A

SUB

STA BETA

ALPHA RESW 1

BEETA RESW 1

INCR RESW 1

Looping and Indexing operation

LDT

LDX #0 : X = 0

MOVECH LDCH STR1, X : LOAD A FROM STR

STCH STR2, X : STORE A TO STR