Subject Name:-
System Programming and
Operating System
1
Savitribai Phule Pune University
Third Year of Computer Engineering (2019
Course)
310243 : Systems Programming and Operating System
Teaching Scheme:
TH: 03 Hours/Week
Credit : 03
Examination Scheme:
In-Sem (Paper): 30 Marks
End-Sem (Paper): 70 Marks
2
Course Objective
To
understand basics of System Programming.
To learn and understand data structures used in design of
system software.
To learn and understand basics of compilers and tools.
To understand functions of operating system.
To learn and understand process, resource and memory
management.
Course Outcome
On
completion of the course, student will be able to–
Analyze and synthesize system software
Use tools like LEX & YACC.
Implement operating system functions.
3
Unit 1
Introduction
4
Input / Output Process Model
Input: keyboard, mouse, scanner, punch cards
Processing: CPU executes the computer program
Output: monitor, printer, fax machine
Storage: hard drive, optical media, diskettes, magnetic tape
10
Typical Computer System
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Major Types of Software
Application software
System software
Hardware
System Software
Operating Systems
Schedules computer events
Allocates computer resources
Monitor events
Language translators
Users
Application Software
Programming languages
Assembly language
FORTRAN, BASIC, PL/1
PASCAL, C
Interpreters
Compilers
Utility programs
Routine operations
(e.g. sort, list, print)
Manage data
(e.g. create files, merge files
14
Need of System Programming
System
programming
is
the
activity
of programming computer system software.
Application programming aims to produce software
which provides services to the user directly (e.g. word
processor), whereas systems programming aims to
produce software and software platforms which provide
services to other software.
Its goal is to achieve efficient use of available resources.
15
Components of System Programming

1.
2.
3.
4.

1.
2.
3.
4.
5.
6.
Program Development Environment:
Text editors
Compilers
Assemblers
Micro processors
Run Time Environment
Linker
Loaders
Debuggers
Interpreter
Operating System
Device Driver
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Text editors
A
text editor is a program that enables you to create and edit text files.
The
distinction between editors and word processors is not clear-cut,
but in general, word processors provide many more formatting features.
They
compose, organise, study and manipulate computer-based
information.
They
allow the user to enter the program in text
Tasks
of editor
Facilitate programmer to enter and save
Allow to modify the code, if needed
code
Examples:
Note
/ Word pad, vi, gedit and many more
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Compiler
Software that translates a high-level language program
into machine language
Input to the compiler is a source file (created by word
processor or editor) containing the text of a high-level
language program.
If it is syntactically correct, compiler will save in an
object file which is a machine language instructions for
the same job.
21
Interpreter
Program execution requires either compiler or
interpreter.
Interpreter accepts the source program and performs
the actions associated with the instructions.
Interpreter reads tge source code one instructon/ line
at a time and converts this lines to a machine code.
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Debugger
It is a tool to facilitate programmer to remove
logical programming errors
Features
Execute program in various modes
Complete,
breakpoint, single stepping
Display contents of the microprocessor and
memory
All
the CPU registers, memory locations in use
Present status of the execution
Present status of flags (psw), location of next
instruction (pc)
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Role of Loader
29
Role of Both Loader and Linker
35
Linker
Linker
combines several object files, resolving
cross references between the files, into one
executable file (machine language program)
36
Role of Loader with Assembler
39
Operating System
Software Component
•Operating System
–API: application program interface
–File management
–I/O
–Kernel
•Memory management
•Resource scheduling
•Program communication
•Security
–Network Module
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Macro processors
Concept
Macro allows a sequence of source language code
to be defined once and then referred to by name
each time it is to be reffered.
Each time this name occurs in the program the
sequence of code is subsituted at that point.
Macro Consist of :
lName of the macro
lSet of parameters
lBody of the macro (Code)
43
Macro Processor
Recognize
macro definitions
Save the macro definition
Recognize macro calls
Expand macro calls
Source
Code
(with
macro)
Macro
Processor
Expande
d Code
Compiler
or
Assembler
obj
44
IDE(Integrated Development
Environment )
Most
high-level languages now include an
Integrated Development Environment (IDE)
consisting of a simple word processor, compiler,
linker and loader tools for finding errors
This
software package provides menus from
which user can select the next step
It
leaves all versions of the program in memory.
For safety, we need to explicitly save the source file
to disk
45
Assembler: Definition
An assembler is a translator which takes its input in the form of an
assembly language program & produces machine language code as its
output.
Translating source code written in assembly language to object code.c
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Machine code
Machine
code:
Set of commands directly executable
Commands in numeric code
Lowest semantic level
via CPU
Machine code language
Structure:
Operation
code
OpCode
Defining executable operation
Operand
OpAddress
address
Specification of operands
Constants/register addresses/storage addresses

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Elements of the Assembly Language
Programming
An
Assembly language is a
machine
dependent,
low level Programming language specific to a certain computer
system.
o Three features when compared with machine language are
1.Mnemonic Operation Codes
2.Symbolic operands
3.Data declarations
Elements of the Assembly Language
Programming
Mnemonic operation codes: eliminates the need to memorize
numeric operation codes.
Symbolic operands: Symbolic names can be associated with
data or instructions. Symbolic names can be used as
operands in assembly statements (need not know details of
memory bindings).
Data declarations: Data can be declared in a variety of
notations, including the decimal notation (avoids conversion
of constants into their internal representation).
Mnemonic Operation Codes
Each
statement has two operands, first operand is always a
register and second operand refers to a memory word using a
symbolic name and optional displacement.
Assembly language-structure
<Label> <Mnemomic> <Operand> Comments

Label
symbolic
labeling of an assembler address
(command address at Machine level)

Mnemonic
Symbolic

description of an operation
Operands
Contains
of variables or addresses if
necessary
Comments
55
Statement format
An Assembly language statement has following format:
[Label] <opcode> <operand spec>[,<operand spec>..]
If a label is specified in a statement, it is associated
as a symbolic name with the memory word
generated for the statement.
<operand spec> has the following syntax:
<symbolic name> [+<displacement>] [(<index register>)]
Eg. AREA, AREA+5, AREA(4), AREA+5(4)
Meaning of Some instructions
MOVE instructions move a value between a memory word
and a register
MOVER – First operand is target and second operand is
source
MOVEM – first operand is source, second is target

All arithmetic is performed in a register (replaces the
contents of a register) and sets condition code.

condition code can be tested by a Branch on Condition
(BC) instruction and the format is:
BC <condition code spec> , <memory address>

Machine Instruction Format

sign is not a part of the instruction

Opcode: 2 digits, Register Operand: 1 digit, Memory
Operand: 3 digits
In a Machine Language Program, all addresses and
constants are shown in decimal as shown in the next
slide
Example: Machine Language Program
Location
Counter
(LC)
MOT
(OPCODE)
Register
Address
Assembly Language Statements
An
assembly program contains three kinds of statements:
1)Imperative Statements
2)Declaration Statements
3)Assembler Directives
Imperative Statements: They indicate an action to be
performed during the execution of an assembled program.
Each imperative statement is translated into one machine
instruction.
Assembly Language Statements
Declaration
Statements: syntax is as follows:
[Label] DS <constant>
[Label] DC '<value>'
The DS (declare storage) statement reserves memory and associates names with
them.
Ex:
A
DS
1 ; reserves a memory area of 1 word, associating the name A
to it
G
DS 200 ; reserves a block of 200 words and the name G is associated
with the
first word of the block (G+6 etc. to access the other words)
The DC (declare constant) statement constructs memory words containing
constants.
Ex:
ONE
DC
'1’ ; associates name one with a memory word
containing value 1

Assembly Language Statements
Assembler Directive
Assembler
directives instruct the assembler to perform
certain actions during the assembly of a program.
Some
assembler directives are described in the following:
1) START
<constant>
This directive indicates that the first word of the target
program generated by the assembler should be placed in the
memory word having address <constant>.
2) END [<operand spec>]
This directive indicates the end of the of the source
program. The optional <operand spec> indicates the address
of the instruction where the execution of the program should
begin.
A simple Assembly Scheme
Design Specification of an assembler
There are four steps involved to design the
specification of an assembler:
Identify information necessary to perform a task.
Design
a suitable data structure to record info.
Determine
processing necessary to obtain and
maintain the info.
Determine
task
processing necessary to perform the
A simple Assembly Scheme
There
are two phases in specifying an
assembler:
1.Analysis Phase
2.Synthesis Phase(the fundamental
information requirements will arise in this
phase)
Tasks Performed : Analysis Phase
Isolate
the labels, mnemonic, opcode and
operand fields of a statement.
If
a label is present, enter (symbol, <LC>) into
the symbol table.
Check
validity of the mnemonic opcode using
mnemonics table.
Update
value of LC.
Analysis Phase
Primary
function of the Analysis phase is
to build the symbol table.
It
must determine the addresses with which
the symbolic names used in a program are
associated
It is possible to determine some addresses
directly like the address of first instruction in
the program (ie.,start)
 Other addresses must be inferred
To determine the addresses of the symbolic
names we need to fix the addresses of all
program elements preceding it through Memory
Allocation.
To implement memory allocation a data structure
called location counter is introduced.
Analysis Phase – Implementing memory
allocation
LC(location
counter) :
is always made to contain the address of the next memory word
in the target program.
 It is initialized to the constant specified at the START
statement.

When
a LABEL is encountered,
it
enters the LABEL and the contents of LC in a new entry of
the symbol table.
LABEL – e.g. N, AGAIN, SUM etc
It
then finds the number of memory words required by the
assembly statement and updates the LC contents
To
update the contents of the LC, analysis phase needs to
know lengths of the different instructions
This
information is available in the Mnemonics table and is
extended with a field called length
We
refer the processing involved in maintaining the LC as
LC Processing
Tasks Performed : Synthesis Phase
Obtain
machine opcode corresponding to the
mnemonic from the mnemonic table.
obtain
address of the memory operand from
symbol table.
Synthesize
a machine instruction or machine form
of a constant, depending on the instruction.
Data structures in synthesis phase
--built by the analysis phase
The two primary fields are name and
address of the symbol used to specify a
value.
Symbol Table
Mnemonics Table --already present
- The two primary fields are mnemonic
and opcode, along with length.
Synthesis phase uses these tables to obtain
The
machine address with which a name is
associated.
The machine op code corresponding to a mnemonic.
The
tables have to be searched with the
Symbol
name and the mnemonic as keys
Data structures of an assembler During analysis and Synthesis phases
Mnemon
ic
Opcod lengt
e
h
ADD
01
1
SUB
02
1
Mnemonic
Table
Source
Program
Analysis
Phase
-------------------------------Synthesis
->
Phase
Target
Program
Symbol Table
Symbol
Address
N
104
AGAIN
113
Data Access
-- > Control
Access
Mnemonics
table is a fixed table which is accessed by
the analysis and synthesis phases
Symbol
table is constructed during analysis and used
during synthesis
Advantages of Assembly Language
•The
primary advantages of assembly language
programming over machine language programming are
due to the use of symbolic operand specifications.
(in comparison to machine language program)
•Assembly
language programming holds an edge over HLL
programming in situations where it is desirable to use
architectural features of a computer.
(in comparison to high level language program)
Assembler’s functions
Convert
mnemonic operation codes to their machine
language equivalents
Convert symbolic operands to their equivalent
machine addresses
Build the machine instructions in the proper format
Convert the data constants to internal machine
representations
Write the object program and the assembly listing
Assembler Design
Pass
of a language processor – one complete scan
of the source program
Assembler Design can be done in:
Single pass
Two pass
Single Pass Assembler:
Does everything in single pass
Cannot resolve the forward referencing
Two pass assembler:
Does the work in two pass
Resolves the forward references
Pass Structure of Assembler
Single Pass Assembler
Single Pass Assembler
Two Pass Assembler
Two Pass Assembler
Task performed by Two Pass Assembler
Task performed by Two Pass Assembler
Two Pass Assembler
Read
from input line
LABEL,
OPCODE, OPERAND
Source
program
Pass 1
OPTAB
SYMTAB
Intermediate
file
Pass 2
SYMTAB
Object
codes
Assembler Design
First pass:
Validate Opcodes
Scan the code by separating the symbol, mnemonic op code and operand
fields .
Assign Address to all the statements in the program
Scan the source for labels and save their values
Perform some processing of assembler directives
Determine the length of areas defined by DC, DS
Build the symbol table
Perform LC processing
Second Pass:
Translate/assemble the instructions
Generate Data Values defined by DC
Process the rest of the assembler directives
Write the Object Code and Assembly Listing
Solves forward references
Converts the code to the machine code
Advanced Assembler Directives
ORIGIN
ORIGIN
<address Specification>
EQU
<symbol>
EQU <address specification>
LTROG
Allocated
address for literals
84
Advanced Assembler
Directives
1. ORIGIN < address specification>
It sets the address of LC to the address given by
address specification.
2. EQU
<symbol> EQU <address specification>
The EQU simply associate the <symbol> with the
<address specifcation>
e.g. BACK EQU LOOP
The symbol BACK is set to the address of LOOP
3. LTORG
At every LTORG statement , memory is allocated
to the literals of the current pool of literals.
85
How to Design an Assembler :
Two Pass Algorithm
Pass 1 (Define symbols):
a.Assign addresses to all statements (LOC)
b.Save the addresses assigned to all labels in symbol
table
c.Perform some processing for assembler directives
Pass 2 (Generate object code):
a.Translate
opcode and operands
b.Generate data values for WORD
c.Write object program
86
An enhanced machine opcode
table (MOT)
87
Intermediate Code Generation
88
Intermediate Code Generation
89