Chapter 9 Instruction Sets: Characteristics and Functions

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Chapter 9Instruction SetsCharacteristicsand
Functions
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Contents

• Machine Instruction Characteristics
• Types of Operands
• Pentium II and PowerPC Data Types
• Types of Operations
• Pentium II and PowerPC Operation Types
• Assembly Language
• Stacks
• Little-, Big-, and Bi-Endian

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What is an instruction set?
Machine instruction characteristics

• The complete collection of instructions that are
  understood by a CPU
• Machine Code
• Binary
• Usually represented by assembly codes

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Instruction Cycle State Diagram
Machine instruction characteristics
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Elements of a Machine Instruction
Machine instruction characteristics

• Operation code (Op code)
• Do this
• Source Operand reference
• To this
• Result Operand reference
• Put the answer here
• Next Instruction Reference
• When you have done that, do this...

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Where have all the Operands gone?
Machine instruction characteristics

• Long time passing.
• (If you dont understand, youre too young!)
• Three areas including source and result operands
• Main memory (or virtual memory or cache)
• CPU register
• I/O device

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Instruction Representation
Machine instruction characteristics

• A Simple Instruction Format
• In machine code each instruction has a unique bit
  pattern
• During instruction execution, and instruction is
  read into an IR in the CPU which must be able to
  extract the data from the various instruction
  fields to perform the required operation

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Instruction Representation
Machine instruction characteristics

• For human consumption (well, programmers anyway)
  a symbolic representation is used
• e.g. ADD, SUB, LOAD
• Common examples
• ADD Add
• SUB Subtract
• MPY Multiply
• DIV Divide
• LOAD Load data from memory
• STOR Store data to memory
• Operands can also be represented in this way
• ADD A,B

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Instruction Types
Machine instruction characteristics

• Example
• X X Y
• Assume that the variable X and Y correspond to
  locations 513 and 514
• Operation
• Load a register with the contents of memory
  location 513
• Add the contents of memory location 514 to the
  register
• Store the contents of the register in memory
  location 513

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Instruction Types
Machine instruction characteristics

• Data processing
• Data storage (main memory)
• Data movement (I/O)
• Program flow control

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Number of Addresses
Machine instruction characteristics

• 3 addresses
• Operand 1, Operand 2, Result
• a b c
• May be a forth - next instruction (usually
  implicit)
• Not common
• Needs very long words to hold everything

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Number of Addresses
Machine instruction characteristics

• 2 addresses
• One address doubles as operand and result
• a a b
• Reduces length of instruction
• Requires some extra work
• Temporary storage to hold some results

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Number of Addresses
Machine instruction characteristics

• 1 address
• Implicit second address
• Usually a register (accumulator)
• Common on early machines

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Number of Addresses
Machine instruction characteristics

• 0 (zero) addresses
• All addresses implicit
• Uses a stack
• e.g. push a
• push b
• add
• pop c
• c a b

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Utilization of Instruction Addresses
Machine instruction characteristics
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How Many Addresses
Machine instruction characteristics

• More addresses
• More complex (powerful?) instructions
• More registers
• Inter-register operations are quicker
• Fewer instructions per program
• Fewer addresses
• Less complex (powerful?) instructions
• instructions of shorter length
• More instructions per program
• Faster fetch/execution of instructions
• more total instructions
• longer execution times and longer,more complex
  programs

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Number of Addresses
Machine instruction characteristics

• One-address instruction
• one general-purpose register (accumulator)
• Multiple-address instruction
• multiple general-purpose register
• Issue of whether an address references a memory
  location or a register
• A machine may offer variety of addressing modes

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Design Decisions
Machine instruction characteristics

• Operation repertoire
• How many ops?
• What can they do?
• How complex are they?
• Data types
• Instruction formats
• Length of op code field
• Number of addresses
• Registers
• Number of CPU registers available
• Which operations can be performed on which
  registers?

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Design Decisions
Machine instruction characteristics

• Addressing modes (later)
• RISC vs CISC

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Types of Operand
Types of operands

• Addresses
• Numbers
• Characters
• Logical Data

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Numbers
Types of operands

• A limit to the magnitude of numbers representable
  on a machine
• A limit to their precision in the case of
  floating-point numbers
• rounding, overflow and underflow
• Three types of numerical data
• Integer of fixed point
• Floating point
• Decimal

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Characters
Types of operands

• ASCII code(unique 7-bit pattern,128 characters)

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Characters
Types of operands

• The eighth bit may be set to 0 or used as a
  parity bit for error detection
• Bit pattern 011XXXX, the digits 0 through 9 are
  represented by their binary equivalents, 0000
  through 1001, in the right-most 4 digits
• Extended Binary Coded Decimal Interchange Code
  (EBCDIC)

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Logical Data
Types of operands

• Two advantages to the bit-oriented view
• Store an array of Boolean or binary data items,
  in which each item can take on only the values 1
  and 0
• Manipulate the bits of a data item

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Pentium II Data Types
Pentium II and PowerPC data types

• 8 bit Byte
• 16 bit word
• 32 bit double word
• 64 bit quad word
• Addressing is by 8 bit unit
• A 32 bit double word is read at addresses
  divisible by 4

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Specific Data Types
Pentium II and PowerPC data types

• General - arbitrary binary contents
• Integer - single binary value
• Ordinal - unsigned integer
• Unpacked BCD - One digit per byte
• Packed BCD - 2 BCD digits per byte
• Near Pointer - 32 bit offset within segment
• Bit field
• Byte String
• Floating Point

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Pentium II Numerical Data Formats
Pentium II and PowerPC data types
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Pentium II Numerical Data Formats
Pentium II and PowerPC data types
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PowerPC Data Types
Pentium II and PowerPC data types

• Data types recognized by fixed-point processor
• Unsigned byte
• used for logical or integer arithmetic operations
• loaded from memory into a general register by
  zero extending on the left to the full register
  size
• Unsigned halfword
• as for unsigned bytes, but, for 16-bit quantities
• Signed halfword
• used for arithmetic operations
• loaded into memory by sign extending on the left
  to full register size

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PowerPC Data Types
Pentium II and PowerPC data types

• Unsigned word
• used for logical operations and as an address
  pointer
• Signed word
• used for arithmetic operations
• Unsigned doubleword
• used as an address pointer
• Byte string
• from 0 to 128 bytes in length

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Types of Operation
Types of operations

• Data Transfer
• Arithmetic
• Logical
• Conversion
• I/O
• System Control
• Transfer of Control

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Common Instruction Set Operation
Types of operations
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Common Instruction Set Operation
Types of operations
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Common Instruction Set Operation
Types of operations
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CPU Actions for Various Types of Operations
Types of operations
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Data Transfer
Types of operations

• Specify
• Source
• Destination
• Amount of data
• May be different instructions for different
  movements
• e.g. IBM 370
• Or one instruction and different addresses
• e.g. VAX

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IBM S/370 Data Transfer Operations
Types of operations
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Arithmetic
Types of operations

• Add, Subtract, Multiply, Divide
• Signed Integer
• Floating point ?
• May include
• Increment (a)
• Decrement (a--)
• Negate (-a)

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Logical
Types of operations

• Bitwise operations
• AND, OR, NOT
• Logical shift the bits of a word are shifted
  left or right. On one end, the bit shifted
  out is lost
• Arithmetic shift treats the data as a signed
  integer and does not shift the sigh bit

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Shift and Rotate Operations
Types of operations
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Shift and Rotate Operations
Types of operations
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Conversion
Types of operations

• change the format or operate on the format of
  data
• E.g. Binary to Decimal

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Input/Output
Types of operations

• May be specific instructions
• May be done using data movement instructions
  (memory mapped)
• May be done by a separate controller (DMA)

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Systems Control
Types of operations

• Executed only while
• the processor is in a certain privileged state
• the processor is executing a program in a special
  privileged area of memory
• CPU needs to be in specific state
• Ring 0 on 80386
• Kernel mode
• For operating systems use

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Transfer of Control
Types of operations

• Branch
• e.g. branch to x if result is zero
• conditional branch instruction
• two ways of generating the condition
• most machines provide a 1-bit or multiple-bit
  condition code that is set as the result of some
  operations
• to perform a comparison and specify a branch in
  the same instruction

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Branch Instructions
Types of operations
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Transfer of Control
Types of operations

• Skip
• implied address
• the implied address equals the address of the
  next instruction plus one instruction length
• e.g. increment and skip if zero
• ISZ Register1
• Branch xxxx
• ADD A

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Transfer of Control
Types of operations

• Procedure Call Instructions
• self-contained computer program incorporated into
  a larger program
• Two principal reasons for the use of procedures
• economy and modularity
• Two basic instructions
• a call instruction branching from the present
  location to the procedure
• return instruction returning from the procedure
  to the place from which it was called

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Transfer of Control
Types of operations

• Nested Procedures

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Transfer of Control
Types of operations

• A procedure can be called from more than one
  location
• A procedure call can appear in a procedure
• allows the nesting of procedures to an arbitrary
  depth
• Each procedure call is matched by a return in the
  called program

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Transfer of Control
Types of operations

• Procedure Call Instructions (continued)
• CPU must somehow save the return address
• the return can take place appropriately
• Common places for storing the return address
• Register
• Start of procedure
• Top of stack

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Transfer of Control
Types of operations

• Procedure Call Instructions (continued)
• If the register approach is used
• CALL X causes the following actions
• RN ? PC ?
• PC ? X
• RN register always used for this purpose
• ? instruction length
• If storing the return address at the start of the
  procedure
• CALL X causes
• X ? PC ?
• PC ? X 1

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Transfer of Control
Types of operations

• Procedure Call Instructions (continued)
• The only limitation of these approaches
• Prevention the use of reentrant procedures
• A reentrant procedure is one in which it is
  possible to have several cells open to it an the
  same time
• A more general and powerful approach
• Stack
• When CPU executes a call
• it places the return address on the stack

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Transfer of Control
Types of operations

• Use of Stack

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Transfer of Control
Types of operations

• Procedure Call Instructions (continued)
• necessary to pass parameters(can be passed in
  registers) with a procedure call
• possible to store the parameters in memory just
  after the CALL instruction
• more flexible approach to parameter passing
• stack
• Entire set of parameters, including return
  address, stored for a procedure invocation
• stack frame

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Transfer of Control
Types of operations
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Pentium II Operation Types
Pentium II and PowerPC operation types
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Pentium II Operation Types
Pentium II and PowerPC operation types
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Pentium II Operation Types
Pentium II and PowerPC operation types
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Pentium II Operation Types
Pentium II and PowerPC operation types
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Call/Return Instructions
Pentium II and PowerPC operation types

• CALL instruction
• pushes the current instruction pointer value onto
  the stack
• causes a jump to the entry point of the procedure
  by placing the address of the entry point in the
  instruction pointer
• ENTER instruction
• added to the instruction set to provide direct
  support for the compiler

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Pentium II Condition Codes
Pentium II and PowerPC operation types
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Pentium II Conditions
Pentium II and PowerPC operation types
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Pentium II Conditions
Pentium II and PowerPC operation types

• With comparison two numbers as signed integers
• use the terms less than and greater than
• With comparison them as unsigned integers
• use the terms below and above

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Pentium II MMX Instructions
Pentium II and PowerPC operation types

• 57 new instructions treating data in a SIMD
  fashion
• possible to perform the same operation, such as
  addition or multiplication, on multiple data
  elements at once
• Each data type is 64-bits in length and consists
  of multiple smaller data fields, each of which
  holds a fixed-point integer
• Packet byte
• Packed word
• Packed doubleword

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MMX Instruction Set
Pentium II and PowerPC operation types
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MMX Instruction Set
Pentium II and PowerPC operation types
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Image Compositing
Pentium II and PowerPC operation types
Alpha
Alpha
B
B
G
G
R
R
Image A
Image A
Unpack byte R pixel components from images A and
B
1.
Subtract
Subtract image B from image A
2.
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Image Compositing
Pentium II and PowerPC operation types
Subtract image B from image A
2.
Multiply result by fade value
3.
Add image B pixels
4.
Pack new composit pixels Back to bytes
5.
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Image Compositing
Pentium II and PowerPC operation types
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PowerPC Operation Types
Pentium II and PowerPC operation types
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PowerPC Operation Types
Pentium II and PowerPC operation types
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Load/Store Instructions
Pentium II and PowerPC operation types

• accesses memory locations in the PowerPC
  architecture
• arithmetic and logical instructions performed
  only on registers
• Two features characterizing the different
  load/store instructions
• Data size
• Sign extension

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Assembly Language
Assembly language

• N I J K (initialize I,J and K to 2,3,4)
• Computation of the Formula N I J K

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Assembly Language
Assembly language

• The program starts in location 101(hexadecimal)
• Memory reserved for the four variables starting
  at location 201
• Four consisted instructions
• Load the contents of location 201 into the AC
• Add the contents of location 202 to the AC
• Add the contents of location 203 to the AC
• Store the contents of the AC in location 204
• Symbolic name or mnemonic of each instruction

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Assembly Language
Assembly language

• Use of the symbolic name or mnemonic of each
  instruction
• The first field contains the address of a
  location
• The second field contains the three-letter symbol
  for the opcode

• With memory-referencing instruction, a third
  field contains the address
• Pseudoinstruction

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Assembly Language
Assembly language

• Use of symbolic addresses
• The first field still for the address
• a symbol used instead of an absolute numerical
  address

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Assembly Language
Assembly language

• Assembly programs are translated into machine
  language by an assembler
• This program not only does the symbolic
  translation discussed earlier, but also assigns
  some form of memory addresses to symbolic
  addresses

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Stacks
Stacks

• An ordered set of elements, only one of which can
  be accessed at a time
• The point of access is called the top of the
  stack
• The number of elements in the stack, or length of
  the stack, is variable
• Also known as a pushdown list or a
  last-in-first-out(LIFO) list

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Stack-Oriented Operations
Stacks
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Typical Stack Organizations
Stacks

• Three addresses needed for proper operation
• Stack pointer
• Stack base
• Stack limit

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Typical Stack Organizations
Stacks

• To speed up stack operations, the top two stack
  elements are often stored in registers

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Expression Evaluation
Stacks

• Applied rules for each element of the expression
• If the element is a variable or constant, push it
  onto the stack
• If the element is an operator, pop the top tow
  items of the stack, perform the operation, and
  push the result

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Comparison of Programs to Calculate f
(a-b)/(cde)
Stacks
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Use of Stack to Compute f (a-b)/(dec)
Stacks
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Conversion of an Expression
Stacks
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Byte Ordering
Little-, big-, and bi-endian

• big-endian
• The mapping on the left stores the most
  significant byte in the lowest numerical byte
  address
• IBM System 370/390, the Motorola 6800, Sun
  SPARC, and most RISC machines
• little-endian
• The mapping on the right stores the least
  significant byte in the lowest numerical byte
  address
• Intel 80x86, Pentium II, VAX, and Alpha
• presents problems when data are transferred from
  a machine of one endian type to the other

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C Data Structure and its Endian Maps
Little-, big-, and bi-endian
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Another View
Little-, big-, and bi-endian
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Byte Ordering
Little-, big-, and bi-endian

• No general consensus as to which is the superior
  style of endianness.
• Points favoring the big-endian style
• Character-string sorting
• Decimal / ASCII dumps
• Consistent order
• points favoring the little-endian style
• big-endian processor has to perform addition when
  it converts a 32-bit integer address to a 16-bit
  integer address, to use the least significant
  bytes
• easier to perform higher-precision arithmetic
• not required to find least-significant byte and
  move backward

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Byte Ordering
Little-, big-, and bi-endian

• PowerPC is a bi-endian processor that supports
  both big-endian and little-endian modes
• The bi-endian architecture enables software
  developers to choose either mode when migrating
  operating systems and applications from other
  machines
• To support this hardware feature, 2 bits are
  maintained in the machine in the MSR maintained
  by the operating system as part of the process
  state

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Bit Ordering
Little-, big-, and bi-endian

• Questions faced with in ordering the bits within
  a byte
• Do you count the first bit as bit zero or as bit
  one?
• Do you assign the lowest bit number to the bytes
  least significant bit(little endian) or to the
  bytes most significant bit(big-endian)