Extra-credit QUIZ Pipelining -due next time-

Transcription

1 QUIZ Pipelining A computer pipeline has 4 processors, as shown above. Each processor takes 15 ms to execute, and each instruction must go sequentially through all 4 processors. A program has 10 instructions. Calculate how long it takes to run it: without pipelining with pipelining 1

2 Extra-credit QUIZ Pipelining -due next time- 2

3 Low-level software Components Circuits Gates Transistors

4 Abstractions and more abstractions You are here 4

5 6.1 Computer Operations Computer = programmable electronic device that can store, retrieve, and process data Von Neumann architecture: Data and instructions to manipulate the data are represented in the same way (binary) and are stored in the same place (memory) For processing, both data and instructions have to be brought into the CPU (fetch-execute cycle) 5

6 6.2 Machine Language Machine language = The language made up of binary coded instructions built into the hardware of a particular computer and used directly by the computer Why would anyone use machine language? (Hint: they had no choice. Why?) Image source: 6

7 Remember: The Fetch-Execute Cycle According to the CPU s machine language 7

8 Characteristics of machine language: Every processor type has its own set of specific machine instructions The relationship between the processor and the instructions it can carry out is completely integrated Each machine-language instruction does only one very low-level task 8

9 Pep/8 Virtual Computer Virtual computer A hypothetical machine designed to contain the important features of a real machine Pep/8 A virtual computer designed by Stanley Warford that has 39 machine-language instructions (We re going to cover only a few of them!) 9

10 Pep/8 Virtual Computer Virtual computer Extra-credit for next time: Figure out what Pep and 8 stand for! A hypothetical machine designed to contain the important features of a real machine Pep/8 A virtual computer designed by Stanley Warford that has 39 machine-language instructions (We re going to cover only a few of them!) 10

11 Pep/8 Registers The program counter (PC) (contains the address of the next instruction to be executed) The instruction register (IR) (contains a copy of the instruction being executed) The accumulator (register A) The memory unit is made up of 65,636 Bytes of storage Can you figure out how long the Pep/8 address is? 11

12 QUIZ The previous version of Pep, Pep/7, could use only 12 bits for memory addresses. How many Bytes of memory could Pep/7 address? 12

13 24 bits 16 bits Explain the address format! 13

14 Can you show what instructions look like in memory? Explain the address format! 14

15 Instruction Format 15

16 Instruction Format Operation code, a.k.a. opcode Specifies which instruction is to be carried out Register specifier Specifies which register is to be used (only use A in this chapter) Addressing-mode specifier Says how to interpret the operand part of the instruction: Direct Immediate Say that again?!? 16

17 Instruction Format Addressing-mode specifier Says how to interpret the operand part of the instruction: Direct Immediate?? Immediate A + B Direct 17

18 Immediate and direct addressing modes 18

19 Immediate and direct addressing modes Example: ADD 42 to accumulator A What exactly am I to add? 19

20 Instruction Format Addressing modes: immediate direct Is there something we are not telling you about Pep s addressing modes? 20

21 QUIZ Pipelining A computer pipeline has 5 stages. Each stage takes 12 ns (nanosec.) to execute, and each instruction must go sequentially through all 5 stages. A program has 20 instructions. Calculate how long it takes to run it: without pipelining with pipelining 21

22 QUIZ Name all the 4 parts of the fetch-execute cycle. What do IR, A, and PC stand for in the computer s architecture? Name and explain the 2 addressing modes we ve covered. 22

23 QUIZ: Immediate and direct addressing SUB 31 from accumulator A What exactly am I to subtract? modes 23

24 PEP/8 machine instructions 24

25 What does this instruction mean, what is its hex code, and what exactly does it do? 25

26 What does this instruction mean, what is its hex code, and what exactly does it do? 26

27 What do these instructions mean, what are their hex codes, and what exactly do they do? 27

28 Wait a second... 28

29 Conclusions It is useless to write operands into IR. IR should be written only in the FETCH stage of the Fetch-Execute cycle, when the 3 bytes of the instruction are brought from memory. Operands can be written only to: Accumulator Memory Some instructions cannot have the immediate addressing mode 29

30 What do these instructions mean, what are their hex codes, and what exactly do they do? 30

31 What does this instruction mean, what is its hex code, and what exactly does it do? Why is there only one on this page?

32 32 What do these instructions mean, what are their hex codes, and what exactly do they do?

33 QUIZ Name all the 4 parts of the fetch-execute cycle. What do IR, A, and PC stand for in the computer s architecture? Name and explain the 2 addressing modes we ve covered. 33

34 Trick QUIZ: Immediate and direct addressing modes We have this Pep instruction: LOAD 20 (decimal) into accum. A What exactly am I to load? 34

35 Problem 16 / 189 The PEP/8 memory has the following contents: 0001 A FF What are the contents of reg. A after this instruction is executed: C

36 0001 A FF Instruction executed: C

37 Problem 17 / 190 The PEP/8 memory has the following contents: 0001 A FF What are the contents of reg. A after this instruction is executed: C The first step is 37

38 Problem 17 / 190 The PEP/8 memory has the following contents: 0001 A FF What are the contents of reg. A after this instruction is executed: C

39 6.3 Program to write "Hello" Every program ends with this! 39

40 Hand Simulation What is the fetch/execute cycle? How much is the PC incremented? What ASCII character is this?

41 Hand Simulation What is the fetch/execute cycle here? What ASCII character is this? 41

42 Your turn! What does this program do?

43 Steps for executing a machine-language program Machine code program in a file on disk Loader Execute Program in memory 43

44 SKIP Pep/8 Simulator 44

45 Problem 33 / 191 The PEP/8 computer has the following program in memory (in hex): Convert the program to binary and explain in your own words what it does. 45

46 Problem 33 / 191 The PEP/8 computer has the following program in memory (in hex): ?? Character input, direct mode, to memory address 0x0008 Character output, direct mode, from memory address 0x0008 STOP ASCII code of character entered by user 46

47 Code (instructions) Remember: In a Von Neumann architecture, code and data are stored in the same memory! ?? Character input, direct mode, to memory address 0x0008 Character output, direct mode, from memory address 0x0008 STOP ASCII code of character entered by user data 47

48 Fact: Writing programs in machine language sucks! (i.e. it is time-consuming, boring, errorprone, unintuitive, etc.) 48

49 that s why they invented assembly language 49

50 6.4 Assembly Language Assembly language A language that uses mnemonic codes to represent machine-language instructions Assembler A program that reads each of the instructions in mnemonic form and translates it into the machine-language equivalent 50

51 Steps for executing an assembly-language program Loader 51 Execute Program in memory

52 Pep/8 Assembly Language Opcode is 04 Opcode is 31 Opcode is 38 Opcode is 39 52

53 Hello program in assembly mnemonic operand addressing mode comments CHARO CHARO CHARO CHARO CHARO STOP.END 0x0048, i ;Outputs character 'H' 0x0065, i 0x006C, i 0x006C, i 0x006F, i What in the world is this?! 53

54 A New Program Problem: Read and sum three values and print the sum How would you do it by hand? 54

55 Declaring variables in assembly: We simply reserve space in memory for them! These are labels. They are placeholders for memory addresses - the assembler will replace them with numeric addresses when generating the machine code! 55

56 Assembler directives, a.k.a. pseudo-ops What is the difference between operations and pseudo operations? 56

57 Completed Program sum:.word 0x0000 num1:.block 2 num2:.block 2 num3:.block 2 main: LDA sum,d DECI num1,d ADDA num1,d DECI num2,d ADDA num2,d DECI num3,d ADDA num3,d STA sum,d DECO sum,d STOP.END 57

58 Completed Program Houston, we have a problem! How does the CPU know that the program starts here? sum:.word 0x0000 num1:.block 2 num2:.block 2 Num3:.BLOCK 2 main: LDA sum,d DECI num1,d ADDA num1,d DECI num2,d ADDA num2,d DECI num3,d ADDA num3,d STA sum,d DECO sum,d STOP.END 58

59 Solution: Branch instruction BR main sum:.word 0x0000 num1:.block 2 num2:.block 2 num3:.block 2 main: LDA sum, d DECI num1, d ADDA num1, d DECI num2, d ADDA num2, d DECI num3, d ADDA num3, d STA sum, d DECO sum, d STOP.END 59

60 QUIZ: Show the memory contents! BR main sum:.word 0x0000 num1:.block 2 num2:.block 2 num3:.block 2 main: LDA sum, d DECI num1, d ADDA num1, d DECI num2, d ADDA num2, d DECI num3, d ADDA num3, d STA sum, d DECO sum, d STOP.END Memory map on next slide 60

61 61

62 sum num1 num2 num3 BR LDA DECI ADDA DECI 62

63 Challenge: Write all the machine code (in hex) sum num1 num2 num3 BR LDA DECI ADDA DECI 63

64 Extra-credit sum num1 num2 num3 BR LDA DECI ADDA DECI 64

65 Your turn! Change the program so it adds up four numbers 65

66 We have covered sections 6.1, 6.2, 6.3, and part of 6.4. Read the text carefully and make sure you can explain in your own words what each instruction accomplishes. Individual work (to do in notebook for next time): 16, 17, 19, EoL2 66