Assembler

Assembler

• 1.
  Assembler A short Overview 1
• 2.
  Content  Language Levels  High Level  micro code  Machinecode language  Assembler languages  Structure  Commands 2
• 3.
  Language Levels High Level Language Assembler Language Machine Language Normally deepest free accessible Level Micro „Firmware“ -programming Hardware 3
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  High Level Micro Code  High Level language  Formulating program for certain application areas  Hardware independent  Assembler languages  Machine oriented language  Programs orient on special hardware properties  More comfortable than machine code (e.g. by using symbolic notations) 4
• 5.
  High Level Micro Code  Machine code:  Set of commands directly executable via CPU  Commands in numeric code  Lowest semantic level  Generally 2 executing oportunities: • Interpretiv via micro code • Directly processing via hardware 5
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  High Level Micro Code  Micro programming:  Implementing of executing of machine commands (Control unit - controller)  Machine command executed/shown as sequence of micro code commands  Micro code commands: • Simpliest process controlling • Moving of data • Opening of grids 6 • Tests
• 7.
  Machinecode language  Machinecode command:  Binary word (fix length, causes elementary operations within CPU)  Machinecode program  sequence of machinecode commands 7
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  Machinecode language  Structure: OpCode OpAddress  Operationcode • Defining executable operation  Operandaddress • Spezification of operands • Constants/register addresses/storage addresses  Difference between 1/2/3 address machines 8
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  Machinecode language  Datatransport commands  Arithmetic and logical commands  Process controlling commands  In-/output commands  Special commands  Disadvantage:  Difficultly readable  No symbolic names(Mnemomics) 9
• 10.
  Assembler languages  Translated into machinecode language(Interpreter)  Each operation code(opcode) owns one symbolic command  Assignments of operand addresses are possible  Labels for command addresses 10
• 11.
  Assembler languages  Usage of pseudo commands  Commands for assembler  Assigment of values/addresses(variables)  Definition of the programstart addresses  Allocating of memory for variables 11
• 12.
  Assembler languages-structure <Label> <Mnemomic><Operand> Comments  Label  symbolic labeling of an assembler address (command address at Machine level)  Mnemomic  Symbolic description of an operation  Operands  Contains of variables or addresse if necessary  Comments 12
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  Assembler Languages - Machine Instructions  Bitpatterns are created, executed as commands by CPU  Classes:  Arithmetic/logical Operations(ADD,SUB,XOR, administrative commands - EQU, shifting&rotation commands)  Data transfer(load/save operations, speicher<>register, register<>register)  Control commands(jump op. [un-]conditional /relativ,control op. – STOP)  In-/output commands 13
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  Assembler – AssemblerInstructiuons (Pseudo Commands)  Instructions to assembler  Controlling translation process  No creation of machine code  Affect creation of machine instructions  Types:  Program organisation  equations and symbolic Addresses  Definition of Constants and Memory  Addressing 14
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  Assembler – Allpurpose Register  Arithmetic example:  Source and Destination Data width has to euqal  AX , BX, CX, DX, SI, DI, BP, SP ; arithmetic operations All purpose ADD AX, BX ; AX := AX+BX Register SUB AH,AL ; AH := AH - AL MOV AL, CL ; AL := CL AX AH AL INC CX ; CX := CX+1 DEC CL ; CL := CL-1 BX BH BL NEG CX ; CX := -CX CX CH CL 15
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  Assembler – SpecialRegister  Unless to all-purpose registers  Special register(SS, DS, CS, ES, IP) • Never ever are • Destination/Source of a „mov“ command • Destination of arithmetic operations 16
• 17.
  Assembler – FlagRegister O D I T S Z A P C Zero Sign Carry Trap Parity Interrupt enable Auxiliary carry Direction Overflow 17
• 18.
  Assembler – FlagRegister  FLAG-Bits:  C Carry Area crossing of unsigned numbers  A Aux. Carry Area crossing at BCD-design  O Overflow Area crossing at arithmetic operation with signed numbers  S Sign True if result = negativ  Z Zero Result = Null  P Parity Result has an even number of 1 Bits  D Direction flag Defines direction of string- commands  I Interrupt Global Interrupt Enable/Disable Flag  T Trap Flag Used by debugger, allows single-step- modus 18
• 19.
  Assembler – FlagRegister  Missing flags: • V: Two’s complement overflow indicator • H: Half Carry Flag  Operations and flags ADD, SUB, NEG affects O, S, Z, A, P, C INC, DEC -“- O, S, Z, A, P MUL, DIV -“- O, C AND, OR , XOR -“- S, Z, P, C 19
• 20.
  Assembler – JumpOperations  Un-/conditioned jumps  Example: Mov AX, 0 CMP CX, 0 again: JZ end (jumpzero, conditioned j.) ADD AX, CX DEC CX JMP again (unconditioned jumped) end: NOP 20
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  Sources http://www.informatik.ku-eichstaett.de /studium/skripte/ws0203/einf2/Vorlesung12.ppt http://www-ist.massey.ac.nz /GMoretti/159704/Lectures/1-Languages-Translation-&-Assemblers.pdf http://www.mathematik.uni-marburg.de /~priebe/lehre/ws0001/ti1/Skript/TechInf1Lo08.ppt E:temp4.SemesterIntro into Dig.ComputingDokuBefehlssatz.pdf 21
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  Thanks 4 urAttention Any further questions ?? 22