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Chapter 10 Instruction Sets: Characteristics and Functions

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1 Chapter 10 Instruction Sets: Characteristics and Functions

2 What is an Instruction Set?
The complete collection of instructions that are understood by a CPU Machine Code Binary Usually represented by assembly codes 2

3 Elements of an Instruction
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... Ref (wikipedia) In mathematics, an operand is one of the inputs (arguments) of an operator For instance, in = 9, '+' is the operator and '3' and '6' are the operands In computer programming languages, the definitions of operator and operand are almost the same as in mathematics. 3

4 Instruction Cycle State Diagram

5 Instruction Representation
In machine code each instruction has a unique bit pattern For human conception, a symbolic representation is used e.g. ADD, SUB, LOAD Operands can also be represented in this way ADD A,B 5

6 Simple Instruction Format

7 Data storage (main memory) Data movement (I/O) Program flow control
Instruction Types Data processing Data storage (main memory) Data movement (I/O) Program flow control 6

8 Number of Addresses (a)
Operand 1, Operand 2, Result a = b + c; May be a forth - next instruction (usually implicit) Not common Needs long words to hold everything 7

9 Number of Addresses (b)
One address is used twice as operand and result a = a + b Reduces length of instruction May require some extra work Temporary storage to hold some results 8

10 Number of Addresses (c)
Implicit second address Usually a register (accumulator) Common on early machines 9

11 Number of Addresses (d)
0 (zero) addresses All addresses are implicitly interpreted Uses a stack e.g. push a push b add pop c c = a + b 10

12 How Many Addresses More addresses Fewer addresses
More complex (powerful?) instructions More registers Inter-register operations are quicker Fewer instructions per program Fewer addresses Less complex (powerful?) instructions More instructions per program Faster fetch/execution of instructions 11

13 In operation code (OP code)
Design Decisions (1) In operation code (OP code) How many ops? What can they do? How complex they are ? Data types Instruction formats Length of op code field Number of addresses 12

14 Design Decisions (2) Registers Addressing modes RISC vs. CISC
Number of CPU registers available Which operations can be performed on which registers? Addressing modes RISC vs. CISC 13

15 Types of Operand Addresses Numbers Characters Logical Data
Integer/floating point Characters ASCII etc. Logical Data Bits or flags 14

16 Addressing is by 8 bit unit
Pentium Data Types Byte : 8 bit Word : 16 bit Double word : 32 bit Quad word : 64 bit Addressing is by 8 bit unit A 32 bit double word is read at addresses divisible by 4 15

17 General - arbitrary binary contents Integer - single binary value
Specific 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 16

18 Pentium Numeric Data Formats
17

19 Some instructions need operand aligned on 32 bit boundary
PowerPC Data Types 8 (byte), 16 (halfword), 32 (word) and 64 (doubleword) length data types Some instructions need operand aligned on 32 bit boundary Can be big- or little-endian Fixed point processor recognises: Unsigned byte, unsigned halfword, signed halfword, unsigned word, signed word, unsigned doubleword, byte string (<128 bytes) Floating point IEEE 754 Single or double precision

20 Types of Operation Data Transfer Arithmetic Logical Conversion I/O
System Control Transfer of Control 18

21 Types of Operation 18

22 Types of Operation 18

23 Types of Operation 18

24 May be different instructions for different movements
Data Transfer 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 19

25 Add, Subtract, Multiply, Divide
Arithmetic Add, Subtract, Multiply, Divide Signed Integer Floating point ? May include Increment (a++) Decrement (a--) Negate (-a) 20

26 Shift and Rotate Operations

27 Logical Bitwise operations AND, OR, NOT 21

28 Conversion E.g. Binary to Decimal 22

29 May be specific instructions
Input/Output May be specific instructions May be done using data movement instructions (memory mapped) May be done by a separate controller (DMA) 23

30 Privileged instructions CPU needs to be in specific state
Systems Control Privileged instructions CPU needs to be in specific state Ring 0 on Most privileged mode, Kernel mode For operating systems use [ source : wikipedia ] 24

31 Transfer of Control Branch Skip Subroutine call
e.g. branch to x if result is zero Skip e.g. increment and skip if zero ISZ Register1 ISZ(Increment operand and skip next instruction if the result is zero) Branch xxxx ADD A Subroutine call c.f. interrupt call < Example of loop > 301 ISZ R1 // initially set to negative value BR 301 // if R1 is zero, then skip next instruction [BR 301] // and code [311] will be executed, // otherwise, loop is executed (i.e., go 301) 25

32 Branch Instruction

33 Nested Procedure Calls

34 Use of Stack

35 Stack Frame Growth Using Sample Procedures P and Q

36 Byte Order (A portion of chips?)
What order do we read numbers that occupy more than one byte e.g. (numbers in hex to make it easy to read) can be stored in 4x8bit locations as follows 27

37 Address Value (1) Value(2) 184 12 78 185 34 56 186 56 34 186 78 12
Byte Order (example) Address Value (1) Value(2) i.e. read top down or bottom up? 28

38 The problem is called Endian Big-endian
Byte Order Names The problem is called Endian Big-endian [ source : wikipedia ] 29

39 Byte Order Names Little-endian [ source : wikipedia ] 29

40 Example of C Data Structure

41 Alternative View of Memory Map

42 Standard…What Standard?
Pentium (80x86), VAX are little-endian IBM 370, Motorola 680x0 (Mac), and most RISC are big-endian Internet is big-endian Makes writing Internet programs on PC more awkward! WinSock provides htoi and itoh (Host to Internet & Internet to Host) functions to convert 30


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