CS.17.A.MachineI.Overview

Transcription

1 P R T I I : L G O R I T H M S, M H I N E S, a n d T H E O R Y P R T I I : L G O R I T H M S, M H I N E S, a n d T H E O R Y omputer Science 7. omputing Machine omputer Science 7. omputing Machine Overview Data types Instructions Operating the machine n Interdisciplinary pproach Section. Machine language programming ROERT SEDGEWIK K E V I N WY N E S.7..MachineI.Overview computing machine Reasons to study Prepare to learn about computer architecture is an imaginary machine similar to: How does your computer's processor work? What are its basic components? How do they interact? ncient computers. Today's smartphone processors. ountless other devices designed and built over the past years. Learn about machine-language programming. How do Java programs relate to your computer? Key to understanding Java references. Intellectual challenge of a new programming regime. Still necessary in some modern applications. multimedia, computer games, embedded devices, scientific computing, Learn fundamental abstractions that have informed processor design for decades. Smartphone processor, s PDP-, 97s 3 4

2 its and words Inside the box Everything in is encoded with a sequence of bits (value or ). Why? Easy to represent two states (on and off) in real world. its are organized in 6-bit sequences called words. More convenient for humans: hexadecimal notation (base 6) 4 hex digits in each word. onvert to and from binary 4 bits at a time. E 7 binary hex D E omponents of machine rithmetic and logic unit (LU) Program counter (P) Instruction register (IR) IR P Holds data and instructions 6 words 6 bits in each word onnected to registers Words are addressable Use hexadecimal for addresses Number words from to Think in hexadecimal Use array notation Example: M[] = 4 LU 6 rithmetic and logic unit (LU) LU D E E D D E D E D E D 's computational engine LU calculator, not a computer Hardware that implements all data-type operations How? Stay tuned for computer architecture lectures Table of 6 words completely specifies contents of memory. 7

3 Program counter and instruction register 6 words, addressable in hex from to (use names R[] through R[]) Scratch space for calculations and data movement. onnected to memory and LU y convention, R[] is always. often simplifies code (stay tuned) Q. Why not just connect memory directly to LU?. Too many different memory names (addresses). Q. Why not just connect memory locations to one another?. Too many different connections. In our code, we often also keep in R[]. R[] R[] R[] E R[3] R[4] R[] R[6] E R[7] R[] R[9] R[] R[] R[] D R[D] R[E] R[] operates by executing a sequence of instructions. ritical abstractions in making this happen Program ounter (P). address of next instruction. Instruction Register (IR). Instruction being executed. etch-increment-execute cycle etch: Get instruction from memory into IR. Increment: Update P to point to next instruction. Execute: Move data to or from memory, change P, or perform calculations, as specified by IR. P EXEUTE IR ETH INREMENT Table of 6 words completely specifies contents of registers. 9 The state of the machine ontents of memory, registers, and P at a particular time Provide a record of what a program has done. ompletely determines what the machine will do. LU and IR hold intermediate states of computation Image sources LU IR P S.7..MachineI.Overview

4 PRT II: LGORITHMS, MHINES, and THEORY data type data type is a set of values and a set of operations on those values. s data type is 6-bit two's complement integers. 7. omputing Machine Overview Data types Instructions Operating the machine Machine language programming Two kinds of operations rithmetic. itwise. ll other types of data must be implemented with software 3-bit and 64-bit integers. 3-bit and 64-bit floating point values. haracters and strings. ll values are represented in 6-bit words. S.7..MachineI.Types 4 data type (original design): Unsigned integers data type (better design): two's complement Values. to 6 Operations. dd. Subtract. Test if., encoded in binary (or, equivalently, hex). Example Warning. ignores overflow. binary hex E Example. E7 + E7 = 3E + = Values. to, encoded in 6-bit two's complement. includes negative integers! Operations. dd. Subtract. Test if positive, negative, or. 6 bit two's complement 6-bit binary representation of x for positive x. 6-bit binary representation of 6 x for negative x. Useful properties Leading bit (bit ) signifies sign. represents zero. dd/subtract is the same as for unsigned. slight annoyance: one extra negative value decimal hex binary +3, ,766 7E +3,76 7D E 3 D 3,766 3,767 3,76 6

5 Two's complement: conversion Overflow in two's complement To convert from decimal to two's complement If greater than +3,767 or less than 3,76 report error. onvert to 6-bit binary. If not negative, done. If negative, flip all bits and add. Examples +3 D ,767 = 7 largest (positive) number = = = = 3,76 smallest (negative) number Examples To convert from two's complement to decimal If sign bit is, flip all bits and add and output minus sign. onvert to decimal. D To add/subtract Use same rules as for unsigned binary. (Still) ignore overflow. Example D = 43 = =D 7 data type: itwise operations ND = x y x ND y Image sources Operations itwise ND. itwise XOR. Shift left. Shift right. XOR = x y x XOR y Shift left 3 fill with s Shift right 3 fill with s Special note: Shift left/right operations also implement multiply/divide by powers of for integers. shift right fills with s if leading bit is 9 S.7..MachineI.Types

6 instructions PRT II: LGORITHMS, MHINES, and THEORY NY 6-bit (4 hex digit) value defines a instruction. opcode instruction halt irst hex digit specifies which instruction. add subtract 7. omputing Machine Overview Data types Instructions Operating the machine Machine language programming Each instruction changes machine state in a well-defined way. category opcodes implements changes operations data-type operations registers data movement flow of control 7 9 D E data moves between registers and memory conditionals, loops, and functions registers, memory P 3 bitwise and 4 bitwise xor shift left 6 shift right 7 load address load 9 store load indirect store indirect branch if zero D branch if positive E jump register S.7..MachineI.Instructions jump and link Encoding instructions program NY 6-bit (4 hex digit) value defines a instruction. Two different instruction formats Type RR: Opcode and 3 registers. Type : Opcode, register, and memory address. Examples opcode destination d source s source t opcode destination d address addr dd R[] to R[] and put result in R[]. Load into R[] data from M[]. opcode instruction RR halt RR add RR subtract 3 RR bitwise and 4 RR bitwise xor RR shift left 6 RR shift right 7 load address load 9 store RR load indirect RR store indirect branch if zero D branch if positive E RR jump register jump and link 3 dd two integers Load operands from memory into registers. dd the registers. Put result in memory. Load into R[] data from M[] Load into R[] data from M[6] dd R[] and R[] and put result into R[] Store R[] into M[7] Halt Q. How can you tell whether a word is an instruction?. If the P has its address, it is an instruction! P D D R[] M[] R[] M[6] R[] R[] + R[] M[7] R[] halt 4

7 Same program with different data dd two integers Load operands from memory into registers. dd the registers. Put result in memory. Load into R[] data from M[] P R[] M[] R[] M[6] R[] R[] + R[] M[7] R[] halt instruction data Load into R[] data from M[6] 7 7 dd R[] and R[] and put result into R[] Store R[] into M[7] Halt Q. How can you tell whether a word is data?. If it is added to another word, it is data! 6 7-9,93 7,339 -,9 S.7..MachineI.Instructions 7. omputing Machine Overview Data types Instructions Operating the machine PRT II: LGORITHMS, MHINES, and THEORY Machine language programming Outside the box User interface Switches. Lights. ontrol uttons. LOD LOOK STEP RUN ON/O irst step: Turn on the machine! S.7.D.MachineI.Operating

8 Loading a program into memory Loading instructions into memory To load an instruction Set memory address switches. Set 6 data switches to instruction encoding. Press LOD to load instruction from switches into addressed memory word. To load an instruction Set memory address switches. Set 6 data switches to instruction encoding. Press LOD to load instruction from switches into addressed memory word. LOD LOOK STEP RUN ON/O : : 6 : 3: 97 4: LOD LOOK STEP RUN ON/O : : 6 : 3: 97 4: 9 3 Loading instructions into memory Loading instructions into memory To load an instruction Set memory address switches. Set 6 data switches to instruction encoding. Press LOD to load instruction from switches into addressed memory word. To load an instruction Set memory address switches. Set 6 data switches to instruction encoding. Press LOD to load instruction from switches into addressed memory word. LOD LOOK STEP RUN ON/O : : 6 : 3: 97 4: LOD LOOK STEP RUN ON/O : : 6 : 3: 97 4: 3 3

9 Loading instructions into memory Looking at what's in the memory To load an instruction Set memory address switches. Set 6 data switches to instruction encoding. Press LOD to load instruction from switches into addressed memory word. To double check that you loaded the data correctly Set memory address switches. Press LOOK to examine the addressed memory word. LOD LOOK STEP RUN ON/O : : 6 : 3: 97 4: LOD LOOK STEP RUN ON/O : : 6 : 3: 97 4: Loading data into memory To load data, use the same procedure as for instructions Set memory address switches. Set 6 data switches to data encoding. Press LOD to load data from switches into addressed memory word. Loading data into memory To load data, use the same procedure as for instructions Set memory address switches. Set 6 data switches to data encoding. Press LOD to load data from switches into addressed memory word. LOD ON : : 6 : 3: 97 4: LOD LOOK STEP RUN ON/O LOD ON : : 6 : 3: 97 4: LOD LOOK STEP RUN ON/O : 6: : 6: 3 36

10 Running a program Switches and lights To run a program, set the address switches to the address of first instruction and press RUN. [ data lights may flash, but all (and RUN light) go off when HLT instruction is reached ] To see the output, set the address switches to the address of expected result and press LOOK. LOD LOOK STEP RUN ON/O : : 6 : 3: 97 4: Q. Did people really program this way?. Yes! : 6: 7: D To run the program again, enter different data and press RUN again PRT II: LGORITHMS, MHINES, and THEORY 7. omputing Machine Overview Data types Instructions Operating the machine Machine language programming S..D.MachineI.Operating S.7.E.MachineI.Programming

11 Machine language programming onditionals and loops instructions support the same basic programming constructs as Java. Primitive data types. ssignment statements. onditionals and loops. rrays (next lecture). Standard input and output (next). any program you might want to write objects functions and modules uses opcodes E and [see book] To control the flow of instruction execution Test a register's value. hange the P, depending on the value. Example: bsolute value of R[] D If R[] > set P to (skip ) Subtract R[] from (R[]) and put result into R[] opcode D instruction branch if zero branch if positive graphics, sound, and image I/O arrays uses opcodes and [see next lecture] Example: Typical while loop (assumes R[] is ) and can support advanced programming constructs, as well. unctions and libraries (see text). Linked structures (see text). primitive data types conditionals and loops Math text I/O assignment statements If R[] is set P to 3 Decrement R[] by 4 Set P to while (a!= ) { a--; } To infinity and beyond! 4 4 Standard input and output Standard input and output n immediate problem We're not going to be able to address real-world problems with just switches and lights for I/O! One solution: Paper tape. Need to bolt new I/O devices to the side of the machine. Punched paper tape Encode 6-bit words in two -bit rows. To write a word, punch a hole for each. To read a word, shine a light behind the tape and sense the holes. STDIN STDOUT mechanism onnect hardware to memory location. To write the contents of a register to stdout, store to. To read from stdin into a register, load from

12 low of control and standard output example: ibonacci numbers reference card Register trace P R[] = R[] = a = ; 4 7 R[] = b = ; R[9] = M[4] i = N; if (R[9] == ) P = 4 while (i!= ) { 4 9 write R[] to stdout StdOut.print(a); 46 R[] = R[] + R[] c = a + b; 47 R[] = R[] a = b; 4 R[] = R[] b = c; R[9] = R[9] - i = i - ; P = 44 } 4 halt 4 STDOUT 3 3 opcode operation format pseudo-code halt halt add RR R[d] = R[s] + R[t] subtract RR R[d] = R[s] - R[t] 3 bitwise and RR R[d] = R[s] & R[t] 4 bitwise xor RR R[d] = R[s] ^ R[t] shift left RR R[d] = R[s] << R[t] 6 shift right RR R[d] = R[s] >> R[t] 7 load addr R[d] = addr load R[d] = M[addr] 9 store M[addr] = R[d] load indirect RR R[d] = M[R[t]] store indirect RR M[R[t]] = R[d] branch zero if (R[d] == ) P = addr D branch positive if (R[d] > ) P = addr E jump register RR P = R[d] jump and link R[d] = P + ; P = addr ormat RR opcode destination d source s source t ormat opcode destination d address ZERO R[] is always. STNDRD INPUT Load from. STNDRD OUTPUT Store to Pop quiz on Pop quiz on Q. What is the interpretation of Q. How does one flip all the bits in a register? 7 as a instruction? 7 as a two's complement integer value? as a instruction? as a two's complement integer value? as a instruction? as a two's complement integer value? (nswer in base 6). 47 4

13 Pop quiz 3 on vs. your laptop Q. What does the following program leave in R[]? 7 R[] = 7 R[] = 7 R[] = 3 R[] = R[] + R[] 4 R[] = R[] - D 3 if (R[] > ) P = 3 6 HLT Two different computing machines oth implement basic data types, conditionals, loops, and other low-level constructs. oth can have arrays, functions, and other high-level constructs. oth have infinite input and output streams. any program you might want to write objects functions and libraries graphics, sound, and image I/O arrays Q. Is 6 words enough to do anything useful?. Yes! (See book, and stay tuned for next lecture.) conditionals and loops Math primitive data types text I/O assignment statements. Yes! It is a Turing Machine, with a read/write I/O device (see theory lectures). OK, we definitely want a faster version with more memory when we can afford it 49 P R T I I : L G O R I T H M S, M H I N E S, a n d T H E O R Y omputer Science omputer Science n Interdisciplinary pproach Section. ROERT SEDGEWIK K E V I N WY N E S.7.E.MachineI.Programming 7. omputing Machine