TK 6123

1. TK 6123 Lecture 14: Instruction Set Architecture Level (Level 2)

2. ISA Level • OS level – ISA level- Microarchitecture level. • Historically, ISA level was developed before any of the other levels (originally the only level). • Sometimes referred as “the architecture” of a machine or “assembly language” (incorrect). • Interface between software and hardware. • The ISA level defines the interface between the compilers and hardware. Prepared by: Dr Masri Ayob

3. ISA Level The ISA level is the interface between the compilers and the hardware. Prepared by: Dr Masri Ayob

4. ISA Level • Is defined by how the machine appears to a machine language programmer. • No person does machine language programming. • Redefined: • ISA-level code is what a compiler outputs. • The compiler writer has to know: • Memory model • Registers • Data type • Addressing mode • Instruction set . Prepared by: Dr Masri Ayob

5. Memory Models • What order do we read numbers that occupy more than one byte • e.g. (numbers in hex to make it easy to read) • 12345678 can be stored in 4x8bit locations as follows Prepared by: Dr Masri Ayob

6. Memory Models (example) • Address Value (1) Value(2) • 184 12 78 • 185 34 56 • 186 56 34 • 186 78 12 • i.e. read top down or bottom up? Prepared by: Dr Masri Ayob

7. Memory Models • The problem is called Endian • The system on the left has the most significant byte in the smallest address: • Big-endian • The system on the right has the least significant byte in the smallest address: • Little-endian Prepared by: Dr Masri Ayob

8. Example of C Data Structure Prepared by: Dr Masri Ayob

9. Standard…What Standard? • Pentium (80x86), VAX are little-endian • IBM 370, Motorola 680x0 (Mac), and most RISC are big-endian • Internet is big-endian. Prepared by: Dr Masri Ayob

10. What is an Instruction Set? • The complete collection of instructions that are understood by a CPU • Machine Code • Binary • Usually represented by assembly codes Prepared by: Dr Masri Ayob

11. Elements of an Instruction • Operation code (Opcode) • Do this…i.e. the task to be performed • Source Operand reference • To this..i.e. the data to be operated on • Result Operand reference • Put the answer here….. • Next Instruction Reference • When you have done that, do this... Prepared by: Dr Masri Ayob

12. Where have all the Operands Gone? • Main memory (or virtual memory or cache) • CPU register • I/O device Prepared by: Dr Masri Ayob

13. Instruction Cycle State Diagram Prepared by: Dr Masri Ayob

14. Instruction Representation • In machine code each instruction has a unique bit pattern • For human consumption (well, programmers anyway) a symbolic representation is used • e.g. ADD, SUB, LOAD • Operands can also be represented in this way • ADD A,B • Usually there are not enough bits in one byte to store enough instructions and addresses: • Instructions stored in more than one byte. Prepared by: Dr Masri Ayob

15. Simple Instruction Format Prepared by: Dr Masri Ayob

16. Number of Addresses (a) • 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 Prepared by: Dr Masri Ayob

17. Number of Addresses (b) • 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 Prepared by: Dr Masri Ayob

18. Number of Addresses (c) • 1 address • Implicit second address • Usually a register (accumulator) • Common on early machines Prepared by: Dr Masri Ayob

19. Number of Addresses (d) • 0 (zero) addresses • All addresses implicit • Uses a stack • e.g. push a • push b • add • pop c Prepared by: Dr Masri Ayob

20. How Many Addresses • More 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 Prepared by: Dr Masri Ayob

21. Design Decisions (1) • Operation issues: • How many ops? • What can they do? • How complex are they? • Data types • Instruction formats • Length of op code field • Number of addresses Prepared by: Dr Masri Ayob

22. Design Decisions (2) • Registers • Number of CPU registers available • Which operations can be performed on which registers? • Addressing modes (later…) • RISC v CISC Prepared by: Dr Masri Ayob

23. Addressing Modes • Instructions can be categorized according to their method of addressing the hardware registers and/or memory. • Implied Addressing • Register Addressing • Immediate Addressing • Direct Addressing • Register Indirect Addressing • Combined Addressing Modes. The various ways of addressing data in an instruction are known as addressing mode. Prepared by: Dr Masri Ayob

24. Implied Addressing • The addressing mode of certain instructions is implied by the instruction’s function. • For example: • the STC (set carry flag) instruction deals only with the carry flag • the DAA (decimal adjust accumulator) instruction deals with the accumulator. Prepared by: Dr Masri Ayob

25. Register Addressing • The accumulator is implied as a second operand. • For example, • the instruction CMP E may be interpreted as 'compare the contents of the E register with the contents of the accumulator. Prepared by: Dr Masri Ayob

26. Immediate Addressing • These instructions have data assembled as a part of the instruction itself. • For example, the instruction CPI 'C' may be interpreted as ‘compare the contents of the accumulator with the letter C. Prepared by: Dr Masri Ayob

27. Direct Addressing • These instructions directly specify the memory address of the operand. • Example: • JMP 1000H causes a jump to the address 1000H by replacing the current contents of the PC with the new value 1000H. • LDA 2000H will loadthe contents of memory location 2000H into the accumulator. Prepared by: Dr Masri Ayob

28. Register Indirect Addressing • These instructions reference memory via a register pair. • For example: MOV M,C • moves the contents of the C register into the memory location pointed by the H and L register pair. • The instruction LDAX B loads the accumulator with the byte of data specified by the address in the B and C register pair . Prepared by: Dr Masri Ayob

29. Combined Addressing Modes • Some instructions use a combination of addressing modes. • A CALL instruction, for example, combines direct addressing and register indirect addressing. • The direct address in a CALL instruction specifies the address of the desired subroutine; • the register indirect address is the stack pointer. The CALL instruction pushes the current contents of the program counter into the memory location specified by the stack pointer. . Prepared by: Dr Masri Ayob

30. Discussion of Addressing Modes A comparison of addressing modes. Prepared by: Dr Masri Ayob

31. Timing Effects of Addressing Modes • Addressing modes affect both: • the amount of time required for executing an instruction. • the amount of memory required for its storage. • For example, instructions that use implied or register addressing, execute very quickly since they deal directly with the processor’s hardware or with data already present in hardware registers. • the entire instruction can be fetched with a single memory access. The number of memory accesses required is the greatest factor in determining execution timing. Prepared by: Dr Masri Ayob

32. Timing Effects of Addressing Modes • More memory accesses require more execution time. • A CALL instruction, for example, requires five memory accesses: three to access the entire instruction and two more to push the contents of the program counter onto the stack. Prepared by: Dr Masri Ayob

33. Types of Operand • Addresses • Numbers • Integer/floating point • Characters • ASCII etc. • Logical Data • Bits or flags Prepared by: Dr Masri Ayob

34. Pentium 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 Prepared by: Dr Masri Ayob

35. Types of Instruction Operation • Data Transfer (data movement) • Arithmetic • Logical • Conversion • I/O • System Control • Program Control Prepared by: Dr Masri Ayob

36. Data Transfer (Data Movement) • 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 • E.g. MOV A,B Move 8-bit data from register B to accumulator A. Prepared by: Dr Masri Ayob

37. Data Transfer (Data Movement) • Data Movement Instructions are the most frequently used and computer designers provide a lot of flexibility to these instructions. • E.g. Intel 8085 provides data transfer between: • Register-to-register • Register-to-memory • Memory-to-register • Stack operation. Prepared by: Dr Masri Ayob

38. Arithmetic • Add, Subtract, Multiply, Divide • E.g. ADD C Add the content of register C to the content of accumulator A. • Signed Integer • Floating point ? • May include • Increment (a++) • Decrement (a--) • Negate (-a) Prepared by: Dr Masri Ayob

39. Shift and Rotate Operations Prepared by: Dr Masri Ayob

40. Logical • Bitwise operations • AND, OR, NOT • Example: ANA B A= A AND B Prepared by: Dr Masri Ayob

41. Conversion • E.g. Binary to Decimal Prepared by: Dr Masri Ayob

42. Input/Output • May be specific instructions • E.g. IN 12 Read input data from port location 12 • May be done using data movement instructions (memory mapped) • May be done by a separate controller (DMA) Prepared by: Dr Masri Ayob

43. Systems Control • Privileged instructions • CPU needs to be in specific state • Ring 0 on 80386+ • Kernel mode • For operating systems use Prepared by: Dr Masri Ayob

44. Program Control Instructions • Branch/Jump • e.g. branch to x if result is zero • JZ • Skip • e.g. increment and skip if zero • ISZ Register1 • Branch xxxx • Subroutine call • E.g. CALL sum • Return from subroutine • E.g. RET Prepared by: Dr Masri Ayob

45. Nested Procedure Calls Prepared by: Dr Masri Ayob

46. Use of Stack Prepared by: Dr Masri Ayob

47. The Pentium 4’s primary registers. Prepared by: Dr Masri Ayob

48. The Pentium 4 Instruction Formats The Pentium 4 instruction formats. Prepared by: Dr Masri Ayob

49. Example of 8051 Instructions More…… Prepared by: Dr Masri Ayob

50. Thank youQ&A Prepared by: Dr Masri Ayob