7300697-assember-sessio 1-ppt

8/13/2019 7300697-assember-Sessio 1-ppt

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ASM Version 1.0ASM Version 1.0 11

Assembler/Session 1

Course Title :

ASSEMBLER

LANGUAGEDuration : 5 Half - DAYS

Course Title ::

ASSEMBLERASSEMBLER

LANGUAGELANGUAGEDurationDuration :: 5 Half5 Half -- DAYSDAYS


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Assembler/Session 1

Course Title :

SSEMBLER L NGU GEDuration : 5 Half - DAYS


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Objectives

Objectives

Familiarise with IBM 370 Assembly Language

Assembler/Session 1


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SESSION 1

Day 1Introduction

SESSION 2

Day 1

Addressing

SESSION 3

Day 2 Machine Instructions

Assembler/Session 1

COURSE SCHEDULE


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Macro LanguageSESSION 8

Day 4

Other TopicsSESSION 9

Day 5

Assembler/Session 1

COURSE SCHEDULE


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Assembler Language

SESSION 1

Assembler/Session 1


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ObjectivesINTRODUCTION

An assembler language is a symbolic form of

machine language

Assembler translates assembler language

program to machine language

An assembler program consists of many

statements

In general, one assembler language statement

corresponds to one machine language

instruction

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ObjectivesSTATEMENT FORMAT

1 10 16 30label operation operands comments

e.g..

INIT1 LA R5,4 ;INITIALISE REGISTER 5

Rules for choosing labels:

maximum 8 characters Alphabets, digits, @, #, $

First character should not be a digit

label should begin in column 1

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Operation

One of the 200 M/C instruction mnemonics

Operand

can be a register or memory location

Continuing a statement

Place any character in column 72 of the line to be continued Continue the statement from column 16 of next line

Maximum 2 continuation lines for a statement

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Comment Statement

* in column 1

Any text in columns 2 - 71

Note : Fields separated by one or moreblanks

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ObjectivesTYPES OF INSTRUCTIONS

1. Machine Instructions

2. Assembler Instructions (Directives)

3. Macro Instructions

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ObjectivesREGISTERS

Registers are storage areas inside the processor

Advantages:

- No need to retrieve data from main storage

(saves time)

- Shared resource that allows intercommunication between programs

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ObjectivesREGISTERS

General purpose registers:

* 16 registers available

* Numbered 0 - 15

* Holds 32 bits (4 bytes) of data

F loating point registers:

* 4 registers available

* Numbered 0,2,4,6* Holds 64 bits (8 bytes) of data

Note : The registers 0, 1, 13, 14 and 15 are reserved for special purpose

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ObjectivesDATA REPRESENTATION

Binary fields

-Always fixed in length, either 2 or 4 bytes

(Fullword or Halfword)

- Negative numbers stored in 2s complement form

Examples:

A DC H295 01 27

B DC H-75 FF 35

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Characters

- One byte (EBCDIC form)

- Character representation of decimal digits is called

Zoned Decimal (first nibble is zone and next is digit)

Zone digit Zone Code

0 - 9 + C- D

+, - , blank Blank F

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F loating Point Numbers

- Always fixed in length, 4, 8 or 16 bytes

(Full word, double word, double double word)

- Left most bit represents sign

(0 - positive; 1 - negative)

- Next 7 bits represent exponent

- Remaining bytes represent the fraction

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Decimal numbers ( Packed Decimal representation)

- Each byte but the rightmost has 2 decimal digits (0-9)

- The right most byte contains a digit in the left half anda sign indicator in the right

Sign indicator: C- Positive

D - Negative

Example: 753 - 7 5 3 C

Assembler/Session 1

A bl /S i 1


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ObjectivesAddressing Operands

Register addressing

Base, displacement addressing

Base, index and displacement addressing

Assembler/Session 1

A bl /S i 6


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ObjectivesI NSTRUCTION FORMATS

RR opcode R1 R2

SI opcode I2 B1 D1

SS opcode L B1 D1 B2 D2

SS opcode L1 L2 B1 D1 B2 D2

RX opcode R1 X2 B2 D2

RS opcode R1 R3 B2 D2

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Assembler Language

SESSION 2

Addressing

Assembler/Session 2

A bl /S i 2


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ObjectivesSTORAGE DEFINITIONS

Two ways to define fields :

1. Define a field and initialise the data in it usingthe DCassembler directive

2. Define a field without initialising using the DSassembler directive

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A bl /S i 2


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Format:

label {DS/DC} dtLnvalue

where :label : Label used to name the field (optional)

d : Duplication factor (optional)

t : Type of data ( required)

Ln : The letter L followed by the length of the field in

bytes (optional)

value : Represents the value enclosed in apostrophes

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Examples:

ALPHA DC CABC EF

FLDS DS 3CL2

H1 DC H29

F2 DC F-10

F1 DC X03

F3 DC PL4-72

Note : for character constants truncation or padding is to

the right and for almost all others it is to the left.

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DC TYPESType Implied Alignment Data Representation

Length

C - None Character

X - None Hex digitsB - None Binary digits

F 4 Full word Binary

H 2 Half word Binary

E 4 Full word Floating point

D 8 Double word Floating point

L 16 Double word Floating point

P - None Packed decimal

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Data Representation in other languages:

Assembler FORTRAN COBOL PASCAL BASIC

Language

DC Type

C Character Display String StringF, H Integer COMP Integer Integer

E Real COMP-1 Real Single

precision

D Double COMP-2 Real DoublePrecision Precision

X, B Logical N/A Boolean Hex

P N/A COMP-3 N/A N/A

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Literals

A literal is a constant preceded by an equals sign =.

Can be used as a main-storage operand but not as adestination field of an instruction

Causes assembler to define a field that is initialised with

the data specified

All constants defined by literals are put by the assembler

in a literal pool, usually at the very end of the program

L R4,=F1

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ObjectivesExercise 1 Q 1 and Q2.

2.What will happen in the following cases

DC CL5123

DC CL5123456

DC XA1245

DC XL2A1245

DC XL5A1245DC F19

DC FL1513

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ObjectivesEQU (Assembler directive)

The EQU statement is used to associate a

fixed value with a symbol

R4 EQU 4

DRBACK EQU OUT+25

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ObjectivesESTABLISHING ADDRESSABILITY

By establishing the addressability of a

coding section, you can refer to the

symbolic addresses defined in it in theoperands of machine instruction

Assembler will convert the implicit

addresses into explicit addresses(base - displacement form)

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To establish the address of a coding section :

Specify a base address from which the

assembler can compute displacements

Assign a base register to contain this baseaddress

Write the instruction that loads the base

register with the base address

Note: The base address should remain in the baseregister throughout the execution of the program

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Establishing Base Register

The USING and DROP assembler instructions

enable one to use expressions representing

implicit addresses as operands of machine

instruction statements, leaving the assignment of

base registers and the calculation of

displacements to the assembler

USING- Use Base Address Register

- allows one to specify a base address and assign

one or more base registers

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To use the USING instruction correctly, one should know :

which locations in a coding section are made addressable

by the USING statement

where in a source module you can use these established

addresses as implicit addresses in instruction operands

Format:

symbol USING base address,basereg1| basereg2|,..

e.g. USING BASE,9,10,11

USING *,12

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Range of a USING instruction:

The range of a USING instruction is the 4096

bytes beginning at the base address specified in

the USING instructionDomain of a USING instruction

The domain of a USING instruction begins

where the USING instruction appears in a source

module to the end of the source module

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The assembler converts implicit address references into theirexplicit form:

if the address reference appears in the domain of a

USING instruction

if the addresses referred to lie within the range of thesame USING instruction

Guideline:

Specify all USING instructions at the beginning of thesource module

Specify a base address in each USING instruction that lies

at the beginning of each control section

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ObjectivesRELATIVE ADDRESSING

Relative addressing is the technique of addressinginstructions and data areas by designating their location

in relation to the location counter or to some symbolic

location

ALPHA LR 3,4

CR 4,6 ALPHA+2 or BETA-4

BCR 1,14

BETA AR 2,3

Note : Always avoid using relative addressing

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Assembler Language

SESSION 3 & 4

Machine Instructions

Assembler/Session 3 & 4



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ObjectivesHANDLING CHARACTER DATA

Move Character Instruction (MVC)

Copy data from one place in memory to another

Format: MVC operand1,operand2

S1(L), S2 - implicit

D1(L,B1),D2(B2) - explicit

e.g...

MVC INPUT(5),OUTPUT




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Move Immediate Instruction (MVI)

Can move only one byte of constant data to a field

Format: MVI operand1,operand2

S1,I2 - implicit

D1(B1),I2 - explicit

e.g..

MVI CTL,CB

DBSS TRAINING CENTRE




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Advanced Techniques

1. Explicit lengths and relative addressing

MVC PAD+6(4),=CL4

PAD DS CL10

2. Overlapping fields and the MVC instruction

MVC FLDB,FLDA

FLDS DC CA

FLDB DS CL3




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Comparison Instructions

Compares 2 values - the values are found in fields, in

registers or in immediate data

CLC - Compare logical charactere.g. CLC FLDA,FLDB

CLI - Compare logical immediate

e.g. CLI FLDA,CK




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ObjectivesExercise 2 Q1 and Q2

2. What will be the effect of the following instructions :

MVI OUTAREA,C

MVC OUTAREA+1(132),OUTAREA

OUTAREA DS 133C

sse b e /Sess o 3 &



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ObjectivesBINARY INSTRUCTIONS

Three types of binary instructions

Full word

Half word

Register

The Binary Move Instructions

L, LH, LR ,ST, STH

Type : R,X Register and indexed storage

e.g... L 5,FULL LR 5,7

STH 7,HALF



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Note : Do not mix up the instruction types and field types

e.g.

LH 5,FULL - right half of Reg 5 gets 1st 2 bytes at FULL

L 6,HALF - Reg 6 gets 4 bytes starting from HALF

ST 3,RES - 4 bytes of reg 3 are stored starting from RES

RES DS H

HALF DC H15

FULL DC F8



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Binary Addition (A, AH and AR)

Fixed-point overflow occurs when the sum will not

fit in the receiving register

Type R-X

e.g.

A 5,FULL

AH 6,HALF

AR 7,3



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Binary Subtraction (S, SH and SR)

Type R-X

e.g.

S 5,FULL

SH 6,HALF

SR 7,3



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Binary comparisons (C, CH and CR)

e.g.

C 5,FULL

CH 6,HALF

CR 7,3

Condition code set as HIGH, LOWor EQUAL



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ObjectivesBinary Multiplication (M, MR, MH)

Format : M op1,op2

op1 : An even numbered register; refers to an even-odd

pair of registers(any register in case of halfword format)

op2 : storage area (fullword/halfword/register)


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Binary Multiplication (M, MR, MH) ...

Function : The value in OP2 is

multiplied by the value in the odd

register of the even-odd pair and theresult placed in even-odd registers

(For half word format : The half word

specified in OP2 is multiplied by the

value in OP1 and result stored in OP1.)



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Binary Division (D, DR)

Format: D op1,op2

Type : R-X / R-R

Op1 : An even numbered register. It refers to an even-odd pairof registers. The pair holds the double word to be

divided. The even register receives the remainder; the

odd register receives the quotient.

e.g. D 4,FULL



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ObjectivesBRANCHING

A branch causes execution to continue at some

other instruction in the program

Branch conditions : B, BH, BL, BE, BNH, BNL,

BNE, BZ, BNZ, BM, BNM, BO, BNO

e.g : CLI FLDA,CK

BNL GOOD



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ObjectivesCONDITION CODE PROCESSING

condition code occupies 2 bits of PSW

condition code is set by each of a number of instructions

condition code is an extremely important intermediary

between arithmetic instructions and conditional branch

instructions

very important in implementing control structures

0 Zero

1 < Zero

2 >Zero

3 Overflow



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ObjectivesBC and BCR Instructions

instructions that do or do not branch depending onthe value of the condition code

Format : BC M1,S2

BCR M1,R2

e.g. BC B1001,BRPTA

will cause a branch to the instruction named

BRPTA, if at the time the instruction is executed,

the condition code is 0 or 3.



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ObjectivesBIT MANIPULATIONS

Operation S-I S-S R-R R-X

OR OI OC OR O

AND NI NC NR N

Exclusive OR XI XC XR X

e.g... OI FLDA,X0F

NR 5,7

X 9,FULL



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Testing individual bits - Test under mask (TM)

TM S1,I2

Function : The bits of S1 ( a single byte) are testedunder the control of the mask in I2 and condition

code is set as all zeroes, all ones or mixed

e.g. TM EMP,B00000101BNM NEXT



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Bit Shifting Instructions

SLL, SLDL Left logical

SRL, SRDL Right logical

SLA, SLDA Left arithmetic (sign bit not affected)

SRA, SRDA Right arithmetic(& condition code set)

e.g. SLL 5,1

SRDA 4,5



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Translations

To translate from one bit combination to another

Format: TR S1(L),S2 or S1,S2

S1 : The field whose data is to be translated

S2 : A 256-byte translation table

Function : The value of the original byte is used as adisplacement into the translation table. The byte found there

replaces the original byte.

e.g. TR WORK,XTABLE



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ObjectivesBINARY CONVERSIONS

1. Conversion to binary (CVB)

Format: CVB operand1,operand2

operand1 : Register

operand2 : a double word (containing

valid packed decimal number)

e.g. CVB 5,DOUBLE

Use : character data -(PACK)->packed decimal-(CVB)->binary



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ObjectivesBINARY CONVERSIONS

2. Conversion from binary (CVD)

Format: CVD operand1,operand2

operand1 : Register

operand2 : a double word

e.g. CVD 5,DOUBLE

Use : binary-(CVD)->packed decimal-(UNPK)->character data



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ObjectivesTABLE PROCESSING

A table is a named storage structure consisting ofsubunits or entries

e.g. RATE DS 6F

L 4,RATE+8

Accessing table elements with indexed storage

operands:

e.g. LH 9,=H2

L 5,RATE(9) (9 - index register)



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ObjectivesMulti-purpose branching instructions

Convenient when counted repetition structure (table processing) is

needed

Branch on count (BCT and BCTR)

Format: BCT op1,op2 (R-X)

Function: First the op1 value is decremented by 1. Second thebranch is taken to the address specified in op2 only if the value in op1

is not 0.

e.g. LH 9,=H12

REPEAT EQU *

..

BCT 9,REPEAT



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Objectives Branch on index high and branch on index low or equal (BXH

and BXLE)

Format: BXLE op1,op2,op3

BXH

op1: A register known as the index register

op2: A even-odd pair of registers

Even register - increment register

Odd register - Limit register

op3: A storage operand. This is the branch addres.



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ObjectivesFunction : First, the value in the increment

register is added to the indexed register. Second,

the branch is taken only when the value in the

index register is lower than or equal to / higher

thanthe value in the limit register

Useful when the same register is to be used as the

count and index register



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ObjectivesBXLE - DO UNTIL repetitions

BXH - DO WHILE repetitionse.g... LH 7,=H0 index

LH 2,=H2 increment amount

LH 3,=H18 the limit

---

REPEAT ...

LH 6,TABLE(7)

...

BXLE 7,2,REPEAT



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ObjectivesLoad instructions with additional features

Load and Test (LTR)

e.g... LTR 15,15

BNZ ERROR

Load Address (LA)

LA R1,D2(X2,B2)



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ObjectivesUSING EQUATES

To associate a fixed value with a symbol

Useful for length and relative address calculation

e.g. TABLE DS 0H

DC C01

DC C02

...

TBLEND EQU *

TBLSIZE EQU TBLEND-TABLE



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ObjectivesUSING EQUATES

Can be used for the following purposes:

1. To assign single absolute values to symbols.

2. To assign the values of previously defined

symbols or expressions to new symbols, thusallowing you to use different mnemonics for

different purposes.

3. To compute expressions whose values areunknown at coding time or difficult to calculate.

The value of the expressions is then assigned to a

symbol.

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Assembler Language

SESSION 5

Program Sectioning

Assembler/Session 5

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ObjectivesBeginning and End of Source Modules

Code a CSECT segment before any

statement that affects the location

counter

END statement is required as the last

statement in the assembly

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ObjectivesCONTROL SECTIONS

A source module can be divided intoone or more control sections

A control section is the smallestsubdivision of a program that can be

relocated as a unit


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At coding time, establish the addressabilityof each control section within the source

module, and provide any symbolic linkages

between control sections that lie in differentsource modules.

Initiated by using the START or CSECT

instruction

CONTROL SECTIONS

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ObjectivesCONTROL SECTIONS

Any instruction that affects the locationcounter, or uses its current value,

establishes the beginning of the first

control section.


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Format of CSECT:

Name Operation Operand

Any symbol CSECT Not required

or blank

Note: The end of a control section or portion of acontrol section is marked by (a) any instruction that

defines a new or continued control section, or (b) the

END instruction.

CONTROL SECTIONS

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ObjectivesDUMMY SECTIONS

A dummy control section is a reference

control section that allows you to describe

the layout of data in a storage area without

actually reserving any virtual storage.


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Use the DSECT instruction to initiate a

dummy control section or to indicate its

continuation.

Format of DSECT:

Name Operation Operand

Any symbol DSECT Not required

or blank

DUMMY SECTIONS

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ObjectivesDUMMY SECTIONS

To use a dummy section :

Reserve a storage area for the

unformatted data Ensure that this data is loaded into the area

at execution time


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Ensure that the locations of the symbols inthe dummy section actually correspond to

the locations of the data being described

Establish the addressability of the dummy

section in combination with the storage area

You can then refer to the unformatted datasymbolically by using the symbols defined in the

dummy section.

DUMMY SECTIONS

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ObjectivesASMBLY2 CSECT

BEGIN BALR 2,0

USING *,2

... Reg 3 points to dataarea

USING INAREA,3

CLI INCODE,C'A'

BE ATYPE

...ATYPE MVC WORKA,INPUTA

MVC WORKB,INPUTB

. .


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WORKA DS CL20WORKB DS CL18

...

INAREA DSECT

INCODE DS CL1

INPUTA DS CL20

INPUTB DS CL18

...

END

A i i

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ObjectivesAssembler Directives

TITLE : To provide headings for each page ofthe assembly listing of the source modules.

EJECT : To stop the printing of the assemblerlisting on the current page, and continue the

printing on the next page.

ORG : To reset the location counter

A bl Di i


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LTORG: A literal pool is createdimmediately after a LTORG instruction or,

if no LTORG instruction is specified, at the

end of the first control section.

PRINT : Tocontrol the amount of detail to

be printed in the listing of programs.PRINT NOGEN / GEN

Assembler Directives

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Assembler Language

SESSION 6

Writing a complete program

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ObjectivesProgram Entry and Exit Logic

Program entry - Preserve register contents

Program Exit - Restore register contents

Register save areaAlways calling program provides a savearea of

18 words long used for storage of registers

Savearea address passed through register 13

A i

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ObjectivesA register save area

Word Address Contents

1 SAV

2 SAV+4 Address of calling programs save area

3 SAV+8 Address of called programs save area

4 SAV+12 Contents of Register 14



...


R ibili i f ll d

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ObjectivesResponsibilities of called program

Program entry conventions1.Save contents of registers 0-12,14 & 15 in

calling programs save area

2.Establish base register

3.Store calling programs save area in the 2nd

word of its own save area

P t ti ( td )

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ObjectivesProgram entry conventions (contd..)

4. Store the address of its register savearea in thethird word of the calling programs register save area

(The addresses in the 3d word of save area establish

a chain of register save areas. This will be useful inreading the dump when program crashes).

R ibiliti f ll d ( td )

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ObjectivesResponsibilities of called program (contd..)

Program Entry

STM R14,R12,12(R13)

BALR R12,0

USING *,R12

ST R13,SAVOWN+4 store calling programs save area

LR R14,R13

LA R13,SAVOWN Reg 13 contains current progs SA...

ST R13,8(R14)


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Program Exit conventions1. Restore registers 0-12 and 14

2. Place the address of the save area provided by thecalling program in Reg 13

3. Place a return code in the low order byte of

register 15 if one is required. Otherwise restoreregister 15.


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Program Exit

L R13,4(R13)

LM R14,R12,12(R13)

BR R4

Responsibilities of calling program

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ObjectivesResponsibilities of calling program

1. Register 13 must contain the address of a register

save area.

2. Register 15 should be set to the beginning address

of the subroutine

L R15,=V(SUBENTRY)

where SUBENTRY is the entry address (usually the CSECT

name) of the subroutine

Responsibilities of calling program (contd )

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ObjectivesResponsibilities of calling program (contd...)

3. Register 14 should have the return address

4. Register 1 sould have the address of the parameter

list

A BALR instruction stores the address of the next

instruction in the calling program into register 14 and

transfers control to the called subroutine

BALR R14,R15

Passing parameters to a subroutine

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ObjectivesPassing parameters to a subroutine

The standard interface requires that addresses of

parameters be placed in a block of storage, and theaddress of the block be loaded into register 1 as the

subroutine is called

Both input and output parameters are treated the sameway

e.g... ADDS DC A(T)

DC A(U)

DC A(V)

LA R1,ADDS

R1 M i t

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ObjectivesR1 Main storage

Addr of parmlist Parmlist parm3

Addr of parm1

Addr of parm2 parm1

Addr of parm3 parm2

C ll d b i B h d

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ObjectivesCalled subroutine B may get the second parameter

by

L R3,4(,R1)

L R8,0(,R3)

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Objectives

Registers with special useR0 : Contains single word output of a

subroutine

R1 : contains the address of an area of

main storage that contains addresses of

parameters

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Objectives

Registers with special use (contd...)R14 : Contains the return address, the address

in the calling routine to which a subroutine

should return control when finished

R15 : contains the address of the entry point in

the subroutine

R13 : contains the address of an area in which

register contents can be stored by a subroutine

The subroutine RANDOM

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ObjectivesThe subroutine RANDOM

RANDOM STM RR14,R12,12(R13)

BALR R12,0

USING *,R12

L R7,RN

M R6,=F65541

ST R7,RN

LR R0,R7

LM R1,R12,24(R13)

BR R14

RN DC F8193

Subroutine RDIGIT

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ObjectivesRDIGIT STM R14,R12,12(R13)BALR R12,0

USING *,R12

ST R13,SAV+4

LA R13,SAV

...

L R15,RANDADBALR R14,R15

...

L R13,SAV+4

LM R14,R15,12(R13)

LM R1,R12,24(R13)

BR R14

SAV DS 18F

RANDAD DC A(RANDOM)

Linkage Conventions

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ObjectivesLinkage Conventions

Program divided into 2 or more sourcemodules

Source module divided into 2 or more control

sections

For link-editing, a complete object module or

any individual control section of the object

module can be specified

C i ti b t t

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ObjectivesCommunicating between program parts

To communicate between 2 or more sourcemodules, symbolically link them together

To communicate between 2 or more control

sections within a source module, establish proper

addressability

Establishing symbolic linkage

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ObjectivesEstablishing symbolic linkage

Identify external symbols in the EXTRN or WXTRN

instruction or the V-type address constant

provide A-type or V-type address constants to reserve

storage for addresses represented by external symbols

In the external source modules, identify these symbols

with the ENTRY instruction

(name entry of a START or CSECT instruction is

automatically identified as an entry symbol)

External symbol dictionary

Establishing symbolic linkage (contd...)Assembler/Session 6


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Objectivesg y g ( )

e.g. program A

EXTRN TABLEB

WXTRN TABLEB

TABADR DS V(TABLEB)

program B

ENTRY TABLEB

TABLEB DS ...

Add C t t (A d V)

Assembler/Session 6


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ObjectivesAddress Constants (A and V)

An address constant is a main storage address containedin a constant

A V-type constant is the value of an external symbol - a

relocatable symbol that is external to the current control

section.Used for branching to locations in other control sections

e.g L 5,ADCON

ADCON DC A(SOMWHERE)

GSUBAD DC V(READATA)

Assembler/Session 7


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Assembler Language

SESSION 7

Assemble and Link Program

Processing of Instructions

Assembler/Session 7


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ObjectivesProcessing of Instructions

Time/ M/C Assembler ENTRY Macro

Activity instruc. EXTRN Instr.

Code source m/c DC,DS

instruc.

Preassembly Refer to macro

instruc.

Assembly object code

LKED

Prog fetch

Execution data area form data

area in load mod

JCL parm processing

Assembler/Session 7


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ObjectivesJCL parm processing

EXEC PGM=pgmname,PARM=

When program gets control :

Register 1 contains the address of a fullwordon a fullword boundary in programs address

space

the high order bit of this fullword is set to 1

(this convention is to indicate the last word in a

variable length parameter list)


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JCL parm processing ...

Bits 1-31 of the fullword contain theaddress of a 2-byte length field on a

halfword boundary

The length field contains a binary countof the no. of bytes in the PARM field

which immediately follows the length

field

COBOL to Assembler

Assembler/Session 7


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ObjectivesCALL asmpgm USING COMM-AREA

PL/I to Assembler

DCL ASMSUB ENTRY OPTIONS(ASSEMBLER)

CHARSTRING CHAR(25);

CALL ASMSUB(CHARSTRING);

Ref : PL/I Programming Guide, COBOL programming

Guide

Assembler/Session 8


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Assembler Language

SESSION 8

Macro Language

Assembler/Session 8


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ObjectivesMacros

Short source routines written and

stored in libraries

Assembler inserts the source

statements in the program where

the macro appears


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Macro Definition

Format :

A header statement

A prototype

Model statements

A trailer statement

Header statement:

Assembler/Session 8


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ObjectivesHeader statement:

MACRO

Prototype:

&name MOVE &TO,&FROM,&LENGTH

Model statements:

A set of machine and assembler instructions

Trailer statement:

&name MEND

Macro Instruction:Assembler/Session 8


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Objectives

A statement containing the name of amacro

when expanded, the symbolic parameters in

the model statements are replaced bycorresponding parameters from the macro

instructions

symbolic prarameters may be positional or

keyword

Macro Instruction ...


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MACRO

&LABEL HALFSWAP &REG,&SV

&LABEL ST &REG,&SV

SLL &REG,8

IC &REG,&SV

SLL &REG,8

IC &REG,&SV+1

MEND

SET Symbols (global or local)

Assembler/Session 8


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ObjectivesSET Symbols (global or local)

3 types :

arithmetic (SETS)

binary (SETB)

character (SETC)

SET symbols are declared using,

LCLA LCLB LCLC

GCLA GCLB GCLC

Format:Assembler/Session 8


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ObjectivesLabel operation operands

symbol-name SETA An expression

SETB

SETC

e.g.

LCLA &A1

GCLA &A2

&A1 SETA 1

&A2 SETA &A1+3

Attributes

Assembler/Session 8


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ObjectivesAttributes

There are 6 attributes of a symbol orsymbolic parameter :

type, length, scaling, integer, count and

number

System variable symbols

&SYSINDX, &SYSDATE, &SYSTIME, &SYSECT,

&SYSPARM, &SYSLOC

Conditional Assembly

Assembler/Session 8


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ObjectivesConditional Assembly

The assembler can be made to branch and loopamong assembler language statements using

sequence symbols and the assembler

instructions AIFand AGO

Sequence symbol : Period followed by 1 to 7

alphabets or digits of which the first is a letter

e.g. .Z23Ab

Format:

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ObjectivesFormat:

Label Operation Operandseq symbo AGO seq. symbol

or blank

-do- AIF A logical expression

enclosed in parenthesis,

followed by seq symbol


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A logical expression is composed of one ormore relations or values of SETB symbols

connected by logical connects AND, OR, AND

NOT, OR NOT

A relation consists of 2 arithmetic expressions

or 2 character expressions connected by a

relational operator EQ, NE, LT, LE, GT, GE

Obj ie.g.

Assembler/Session 8


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ObjectivesMACROPSRCH &PARAMS,&STRING

GBLB &FOUND

LCLA &I

&FOUND SETB 0

.LP AIF ((&I GE N&PARAMS) OR &FOUND) .E

&I SETA &I+1

&FOUND SETB (&PARAMS(&I) EQ &STRING)

AGO .LP

.E MEND

Assembler/Session 9


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Assembler Language

SESSION 9

Other Topics

Obj i

Assembler/Session 8


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ObjectivesCharacteristics of good assembler program

has simple, easy to understand logic

uses mostly simple instructions

has no relative addressing

uses subroutines

Ch t i ti f d bl


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Characteristics of good assembler program ...

uses DSECTs

has efficient code (LA R10, 4(0,R10 - A R10,=F4)

does not abnormally terminate due to user error

requests and check feedback from macro instruction

provides meaningful error messages

Obj iCharacteristics of good assembler program

Assembler/Session 8


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ObjectivesCharacteristics of good assembler program

(contd..)

lets the assembler determine lengths

has opcodes, operand and comments aligned

contains meaningful comments

uses meaningful labels

Obj tiStructured Programming

Assembler/Session 8


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Objectivesg g

To improve design and understandability of aprogram

made up of building blocks of subroutines

Conventions for general purpose registers

Base registers

Link registers

Obj tiThe EXecute Instruction

Assembler/Session 9


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Objectives

the EX instruction is a R-X type instruction thatdirects the execution of an instruction called the

subject instruction, which is addressed by the second

operand

the subject instruction is in effect a one-instruction

subroutine

The EXecute Instruction (contd...)


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The subject instruction is modified before execution(though not altered at its main storage location) : bits

8-15 of the instruction ORed with bits 24-31 of

register R1 to form the second byte of the instructionactually executed

e.g. Let reg 9 have the length of string to be moved

EX R9,VARMVC

VARMVC MVC A(0),B

The EXecute Instruction (contd...)

Obj ti

DEBUGGING

Assembler/Session 9


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Objectives

Exceptions and InterruptsInterrupts that result directly from attempts at invalid

program execution are called program-check

interrupts; identified by a code

Interruption code 1 : Operation

Interruption code 2 : Privileged operation

Interruption code 4 : Protection

Interruption code 5 :Addressing

Interruption code 6 :Specification

Obj ti

DEBUGGING

Assembler/Session 9


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Objectives

Exceptions and Interrupts (contd..)

Interruption code 7 : Data

Interruption code 8 : Fixed-Point Overflow

Interruption code 9 : Fixed-Point Divide

Other Interruption codes ( 3, 10, 11, 12, 13,14, 15)

Obj ti

DEBUGGING

Assembler/Session 9


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Objectives

Reading dumps

whenever a program abends an indicative

dump is generated

The completion code is a code furnished by

the O/S to designate the reason for the

termination of the job step

In case of program check interruption, the first

2 digits of the completion code is 0C

DEBUGGING


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Locate the entry point of your program

Reading dumps ...

Obj ti

DEBUGGING

Assembler/Session 9


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Objectives

Reading dumps (contd...)

The register contents are the contents at the

point of interruption (the instruction that

caused the interrupt is usually the one justbefore the interrupt address given)

use address at interrupt and entry address to

locate the instruction that caused the program-check interruption

Obj ti

DEBUGGING

Assembler/Session 9


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Objectives

Full and Partial dumps

//SYSUDUMP DD SYSOUT=A

SNAP macro

DEBUGGING


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Reading the dump

SAVE AREA trace

P/P Storage

Examine register contents, PSW and listed entry

point to find the portion of program being executed

Look at main storage dump to determine the databeing used

Objectives

SYSTEM MACROS

Assembler/Session 9


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ObjectivesData Management Macros

DCB - Construct a data control block

OPEN - Logically connect a dataset

CLOSE - Logically disconnect a dataset

GET - Obtain next logical record (queued access)

PUT - Write next logical record (queued

access)

READ - Read a block (basic access)

WRITE - Write a block (basic access)

Objectives

SYSTEM MACROS

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Objectives

Supervisor Services MacrosABEND - Abnormally terminate a task

CALL - Pass control to a control section

GETMAIN - Allocate virtual storage

FREEMAIN - Free virtual storage

LOAD - Bring a load module into virtual storageRETURN - return control to the calling program

SAVE - Save register contents

Objectives

SYSTEM MACROS

Assembler/Session 9


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Objectives

Supervisor Services Macros (contd)

SNAP - Dump virtual storage and continue

LINK - Pass control to a Program in

Another load module

WTO - Write to operator

Objectives

SYSTEM MACROS

Assembler/Session 9


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Objectivese.g. File I/O

OPEN (INFILE,INPUT)

GET INFILE,RECAREA

PUT OUTFILE,RECAREA

CLOSE (INFILE)

INFILE DCB

DSORG=PS,MACRF=GM,DDNAME=IFILE

OUTFILE DCB

DSORG=PS,MACRF=PM,DDNAME=OFILE

(RECFM=,LRECL=,BLKSIZE=,)

Objectives

SYSTEM MACROSAssembler/Session 9


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ObjectivesThree forms :

Standard form : Results in instructions that store

into an inline parameter list and pass control to the

required program

List form : Provides asn out-of-line parameter list

Execute form : Provides the executable instructions

required to modify the out-of-line parameter list

and pass control to the required program


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7300697-assember-sessio 1-ppt

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