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ICS 51 Introductory Computer Organization. Fall 2009. Agenda. Computer System Assembly Language (to help w/ lab) Introduction of Assembly Language Data types and registers Instruction categories. Computer System. Storage Architecture. Closer to CPU Faster. Hard Disk. Memory.

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Ics 51 introductory computer organization

ICS 51Introductory Computer Organization

Fall 2009


Agenda
Agenda

  • Computer System

  • Assembly Language (to help w/ lab)

    • Introduction of Assembly Language

    • Data types and registers

    • Instruction categories



Storage architecture
Storage Architecture

Closer to CPU

Faster

Hard Disk

Memory

Registers

Larger

Space


Registers
REGISTERS

  • A type of internal fast memory

    • Assume operations are on register operands

    • Very few in x86 - only 8!

  • Need to know how to “address” them

    • For example, Add R1, R2

      • means R1 = R1 + R2

  • All x86 computation instructions are of the form

    • Op Rx, Ry

      • Op indicates operation

      • Rx and Ry present operands

        • Rx is destination operand

        • Rx and Ry are source operands

      • For example: Add R1, R2

        • R1 = R1 + R2


Assembly language
Assembly Language

  • High level language

    • C, C++, Java language

    • Abstraction

    • Human friendly

      (e.g.)

      a = b + c;

  • Assembly language

    • X86 Assembly language for Intel machine

    • Hard for human to read

      (e.g.)

      Mov eax, b

      Mov ebx, c

      Add eax, ebx

      Mov a, eax

    • High efficiency to use registers

  • Machine language

    • Machine code for a specific machine

    • Machine readable

      (e.g.)

      00110100100100100100111010101010

      10100100100100100111010101010111

      10101010101111101010101011110010


Assembly language programming
Assembly Language Programming

  • Assembly Language

    • Processor-specific, low-level programming language

      • exposes most of processor features to the programmer

    • Describes

      • Data types and operations

        • Size: Byte, Word, etc

        • Meaning: integer, character

      • Storage

        • Registers

        • Memory

      • Specific instructions

  • Will use Intel Assembly (x86, IA-32)

    • A small subset of all instructions


Generic instructions
Generic Instructions

  • Specify operation and operands

  • Simple enough for hardware to execute directly

  • For example: SUB R4, R3

    • Operation is subtract

    • Operands are contents of memory locations called or addressed as R4, R3


Data types size
Data Types - size

Always take care of the type of data an instruction accesses!!!!


Operands
Operands

  • The registers are operands of the instruction

  • There are source and destination registers

  • AND R7, R5

    • R7 = R7 AND R5

      • R7 is the destination operand (register)

      • R7 and R5 are source operands (registers)


X86 examples
X86 Examples

  • Add EAX, EBX

    • Add the contents

  • Is the same as earlier example: Add R1, R2

    • here operands are in registers called R1 and R2

  • Intel uses the following names for 32b registers

    • EAX for R1, EBX for R2

    • ECX for R3, EDX for R3

    • The other four are registers called ESI, EDI, EBP, ESP

  • Use only Intel register names in Assembly



  • (E)AX, BX, CX, and DX are general purpose registers

    • AX is usually called accumulator register, or just accumulator. Most of arithmetical operations are done with AX.

    • BX is usually called base register. The common use is to do array operations. BX is usually used with other registers, most notably SP to point to stacks.

    • CX is commonly called counter register. This register is used for counter purposes.

    • DX register is the data register. It is usually used for keeping data value.

  • CS, DS, ES, and SS are segment registers

    • You do not need to fiddle with these registers.

  • SI and DI are index registers

    • Usually used to process arrays or strings. SI is called source index and DI is destination index.

  • BP, SP, and IP are pointer registers

    • BP is base pointer. Used for preserving space to use local variables in C/C++ (the same as frame pointer?) Don’t need to fiddle with it.

    • SP is stack pointer. Points to the last used location in the stack.

    • IP is instruction pointer (it is the same as PC or program counter on other architectures). Points to the instruction that is going to be executed next. Cannot be directly modified.


Flag register
Flag register

  • Flag is a register that contains processor status

    • No direct access to it

    • C: carry flag (bit 0). Turns to 1 whenever the last arithmetical operation has carry or borrow, otherwise 0.

    • P: parity flag (bit 2). It is set to 1 if the last operation result has even number of 1’s.

    • A: auxiliary flag (bit 4). It is set in Binary Coded Decimal (BCD) operations.

    • Z: zero flag (bit 6). Is 1 if the last operation result is zero.

    • S: sign flag (bit 7). It is set to 1 if the most significant bit of the last operation is 1.

    • T: trap flag (bit 8). It is only used in debuggers to turn on the step-by-step feature.

    • I: interrupt flag (bit 9). Disables or enables interrupts.

    • D: direction flag (bit 10). If set, all string operations are done backward.

    • O: overflow flag (bit 11). If the bit is set, the last arithmetic operation resulted in overflow.

    • IOPL: I/O Privilege Level flag (bit 12 to 13). It is used to denote the privilege level of the running programs.

    • N: Nested Task flag (bit 14). Used to detect whether multiple tasks (or exceptions) occur.

  • Most often used flags are O, D, I, S, Z, and C.


Instruction categories
Instruction Categories

  • Data movement instructions

  • Arithmetic operations

  • Logical operations

  • Comparison instructions

  • Control Transfer Instructions

    • Unconditional

    • Conditional


Data movement instructions
Data Movement Instructions

REGISTER, REGISTER1 and REGISTER2 can be any of the Intel registers (EAX, EBX, ECX, etc)

  • Between registers

    mov REGISTER1, REGISTER2

  • To registers

    mov REGISTER, value

    mov REGISTER, variable

  • To a variable

    mov variable, REGISTER

  • From a variable

    mov REGISTER, variable


Simple arithmetic operations
Simple Arithmetic Operations

add REGISTER, VALUE

  • REGISTER = REGISTER +VALUE

    add REGISTER1, REGISTER2

  • REGISTER1 = REGISTER1 +REGISTER2

    sub REGISTER, VALUE

  • REGISTER = REGISTER -VALUE

    sub REGISTER1, REGISTER2

  • REGISTER1 = REGISTER1 -REGISTER2


Boolean operation instructions
Boolean Operation Instructions

  • NOT

  • AND

  • OR

  • XOR

  • Example: OR EAX, EBX

  • One way to set a register to 0

    • XOR R1, R1

      • (R1 AND (NOT R1) OR ((NOT R1) AND R1)


Comparison instructions
Comparison Instructions

CMP Op1,Op2

cmp REGISTER, VALUE

cmp REGISTER1, REGISTER2

  • Sets special registers called flags

    • Each flag 1-bit storing 0 or 1

  • x86 has the following flag registers

    • N, Z, C, V

  • Flags are used by the conditional jumps


Control transfer instructions
Control Transfer Instructions

  • Instructions execute sequentially, except for CTI

  • Unconditional Transfer Instructions

    • e.g.) jmp Label

  • Conditional Transfer Instructions

    • e.g.) jg Label

  • Labels

    a_label:

    ...

    CODE

    ...

    another_label:

    ...



Conditional transfer instructions
Conditional Transfer Instructions

jg LABEL

greater

jge LABEL

greater or equal

jl LABEL

less

jle LABEL

less or equal

je LABEL

equal

jne LABEL

not equal


Lab assignments
Lab Assignments

  • You will use assembly blocks inside C programs

  • Visual Studio is the software tool we use in the lab



int sum (int firstparam, int secondparam)

{ int retval;

__asm {

mov eax, firstparam

mov ebx, secondparam

add eax, ebx

mov retval, eax

}

return retval;

}


Turning in lab assignments
Turning in Lab Assignments

  • Start lab assignment ASAP

  • Turnins past the deadline are automatically

    rejected


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