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Instruction Set Architecture

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Introduction to Instruction Set Architecture and Assembly programming with PIC Instruction Set

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Instruction Set Architecture

  1. 1. Instruction Set Architecture CS2052 Computer Architecture Computer Science & Engineering University of Moratuwa Dilum Bandara Dilum.Bandara@uom.lk
  2. 2. Blocks of a Microprocessor 2 Literal Address Operation Program Memory Instruction Register STACK Program Counter Instruction Decoder Timing, Control and Register selection Accumulator RAM & Data Registers ALU IO IO FLAG & Special Function Registers Clock Reset Interrupts Program Execution Section Register Processing Section Set up Set up Modify Address Internal data bus Source: Makis Malliris & Sabir Ghauri, UWE
  3. 3. Instruction Set Architecture (ISA) 3 Instruction Set Software Hardware Source: Computer Architecture: A Quantitative Approach, J. L. Hennessy & D. A. Patterson, 3rd Edition.
  4. 4. ISA (Cont.)  Part of computer architecture related to programming  Include native data types, instructions, registers, addressing modes, memory architecture, interrupt & exception handling, & external I/O  e.g., R1, R2, …, PC  e.g., MOV, ADD, INC, AND  ISA specifies the set of opcodes (machine language), & native commands implemented by a particular processor 4
  5. 5. Well Known ISAs  x86  Based on Intel 8086 CPU in 1978  Intel family, also followed by AMD  X86-64  64-bit extensions  Proposed by AMD, also followed by Intel  ARM  32-bit & 64-bit  Initially by Acorn RISC Machine  ARM Holding  MIPS  32-bit & 64-bit  By Microprocessor without Interlocked Pipeline Stages (MIPS) Technologies 5
  6. 6. Well Known ISAs (Cont.)  SPARC  32-bit & 64-bit  By Sun Microsystems  PIC  8-bit to 32-bit  By Microchip  Z80  8-bit  By Zilog in 1976  Many extensions  Intel – MMX, SSE, SSE2, AVX  AMD – 3D Now! 6
  7. 7. A Good ISA  Lasts through many implementations  Portability, compatibility  Used in many different ways  Servers, desktop, laptop, mobile, tablet  Provides convenient functions to higher layer  Permit efficient implementation at lower layer 7
  8. 8. Example – Instructions  Microprocessor that we are going to build will support following 2 instructions  ADD  LOAD 8
  9. 9. Activating Necessary Blocks 9 Source: www.transtutors.com/homework-help/computer- science/computer-architecture/cpu/general-register-organization/
  10. 10. Micro-operations  Digital modules are best described by  Registers they contain  Micro-operations performed on data stored on those registers  Elementary operations done on data in registers  Register Transfer Language  Concise symbolic expressions  ADD  ADD RC, RA, RB RC  RA + RB PC  PC + 1  LOAD  LOAD RA, d RA  d PC  PC + 1 10
  11. 11. How to Describe a Computer  Set of registers & their functions  Sequence of micro-operations  Controls that initiates & maintains sequence of micro-operations  Today, from a programming point of view, Assembly is the lowest level we use to define these registers, instructions, & their order of execution 11
  12. 12. Programming in Assembly  To program in Assembly we need 1. Knowledge about hardware design  Registers  Memory addressing  I/O 2. Knowledge about instruction set 12
  13. 13. Registers (Review)  Type of memory located inside CPU  Can hold a single piece of data  Useful in both data processing & control functionalities  Types  Special purpose registers  Program counter (PC)  Instruction register (IR)  Accumulator or working register (A or W)  Flag register (FLAG or STATUS)  General purpose registers  No special name, typically A, B, C, ... Or R1, R2, R3, ... 13
  14. 14. Format of an Assembly Statement 14 [Identifier / Label] Operation/ Command/ Op code [Operand(s)] [;Comment] Labeling code or to indicate a program destination address for jumps What instruction to be carried out by CPU Only valid instructions are allowed Data or register contents to be used in instruction Some instructions don’t need operands Explanatory text. Optional but very useful, as Assembly programs are hard to understand L20: ADD RC, RA, RB ;RC  RA + RB
  15. 15. Example – Instruction Set  We’ll use instruction set from PIC 16F87x for our discussion  Textbook doesn’t use a specific set  Most other textbooks may use MIPS or x86  They are still too complex to start with  When you are more familiar, you can learn/use any new instruction set 15
  16. 16. 16 F file register W working register B bit L literal (number) Z conditional execution d destination bit d=0 store in W d=1 store in f use , w or ,f instead Source: Makis Malliris & Sabir Ghauri, UWE
  17. 17. Opcode  Determines the instruction  Registers, bits, literals depend on the opcode field 17 Source: PIC16F87X Data Sheet by Microchip Technology Inc.
  18. 18. Assembler  Assembler translates human readable code into binary  Binary code specifies opcode & operands  ADDLW 135 means “add literal 135 to W register”  Assembler converts this to 11 1110 1000 0111  This is what the machine understands 18
  19. 19. Program Operations  Load a register with a given number  Copy data from register to another  Carry out arithmetic & logical operations on a data word or a pair of data words  Test a bit or word & jump, or not, depending on result of the test  Jump to a point in the program  Jump to a subroutine  Carry out a special control operation 19
  20. 20. Instruction Classification Instruction Types  Data transfers  Arithmetic, logic  Rotates, shifts  Bit set, bit reset, & bit test  General-purpose, CPU control  Jumps  Calls, returns Instruction Function  Move  Register  Arithmetic  Logic  Test & Skip  Jump 20
  21. 21. Data Transfer Instructions  Used to transfer data from one location to another  Register to Register, Register to Memory, Memory to Register  MOV  MOVLW 3 ; W  03h  MOVWF R1 ; R1  03h  MOV is same as LDA (Load) in textbook 21
  22. 22. Arithmetic Instructions  Used in arithmetic operations  ADD – ADDWF R1 ; W  W + R1  ADD – ADDLW 3 ; W  W + 3  SUB – SUBLW 5 ; W  W - 5  INC – INCF R1 ; R1  R1 + 1 22
  23. 23. ALU (Review)  Data processing unit  Arithmetic unit  Performs arithmetic operations  Logic unit  Performs logical operations 23 Accumulator Source: Introduction to PIC Microcontroller – Part 1 by Khan Wahid
  24. 24. Example – Arithmetic Instructions  Write an assembly program to add 5 & 10  Steps  How many registers?  What registers to use?  What instructions are required?  MOV – MOVLW 5 ; W  05h  ADD – ADDLW 0xA ; W  05h + Ah 24
  25. 25. Logic Operations  Used in bitwise logic operations  AND – ANDLW 3 ; W  W & 0011  OR – IORLW 3 ; W  W | 0011  XOR – XORLW 3 ; W  W  1001  NOT – COMF 0x20,1 ;(0x20)  (0x20)/ 25
  26. 26. Example – Logic Operations  Example  Write an assembly program to convert a given character from uppercase to lowercase & vice versa  If we consider ASCII, this can be achieved by changing the 5th bit  A = 65 =0x41 = 0 1 0 0 0 0 0 1  a = 97 =0x61 = 0 1 1 0 0 0 0 1  Get XOR with 00100000 = 32 = 0x20 26
  27. 27. Transfer Instructions (Jump Instructions)  Can be used to jump here & there within program  Can be used to control loops  GOTO – GOTO loop ;go to loop label  CALL – CALL delay ;call delay subroutine 27
  28. 28. Example – Transfer Instructions  Example  Write a program to calculate the total of all integers from 1 to 10  High-level program 28 int total = 0; for (int i=1 ; i<=10; i++) { total += i; }
  29. 29. Example – Transfer Instructions (Cont.)  Steps  Are there any conditions/loops?  How many registers?  What registers to use?  What instructions to use?  ADDLW  Increment/decrement instruction – INCF, DECF  Let’s use memory address 0020h 29
  30. 30. Transfer Instructions (Cont.) 30 start movlw 0xa ; w  10 movwf 0x20 ; (0x20)  w movlw 0 ; total loop addwf 0x0020,0 ; Add decf 0x0020,1 ; Dec counter btfss STATUS,Z ; is counter 0? goto loop ; repeat nop end int total = 0; for (int i=10 ; i!=0; i--) { total += i; }
  31. 31. 31 Homework  Example  Write an assembly program to multiply 3 & 4  Steps:  How many registers?  What registers to use?  What instructions to use?  MOV – MOVLW 3 ; W  03h  MUL – ???
  32. 32. Shift Operators >> <<  Move all bits in a value by given no of positions to left or right 10011011 01110110 10010011 >> 1 >> 3 >> 3 01001101 00001110 00010010 10011011 01110110 <<1 <<3 00110110 10110000  Multiply by powers of 2 – value << n (value * 2n)  e.g., 4 << 3 ; (4 * 8) =32  Divide by powers of 2 – value >>=n (value / 2n)  e.g., 75 >> 4; 75 / 16 =4 32
  33. 33. Rotate Through Carry  RLF – Rotate Left f through Carry  Suppose carry was 1  RLF 9B  1 = 37  RLF 9B  2 = 6F  RRF – Rotate Right f through Carry  Suppose carry was 1  RRF 9B  1 = CD  RRF 9B  2 = E6 33
  34. 34. Comparison Operations  Comparing 2 numbers need to be treated with care due to non-intuitive nature of Carry flag movlw 2 ; W = 2 subwf Q, W ; W = Q - 2 btfss STATUS, C ; check carry flag goto Gr_eq ; Q >= 2 goto Less ; Q < 2 34

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