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CS/COE0447 Computer Organization & Assembly Language

Introduction to computer organization and assembly language concepts. Includes concepts of program execution, number representation, and program performance.

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CS/COE0447 Computer Organization & Assembly Language

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  1. CS/COE0447Computer Organization & Assembly Language Pre-Chapter 2

  2. void swap(int v[], int k) { int temp; temp = v[k]; v[k] = v[k+1]; v[k+1] = temp; } swap: muli $2, $5, 4 add $2, $4, $2 lw $15, 0($2) lw $16, 4($2) sw $16, 0($2) sw $15, 4($2) jr $31 00000000101000010… 00000000000110000… 10001100011000100… 10001100111100100… 10101100111100100… 10101100011000100… 00000011111000000… assembler compiler “C Program” Down to “Numbers”

  3. 00000000101000010… 00000000000110000… 10001100011000100… 10001100111100100… 10101100111100100… 10101100011000100… 00000011111000000… “Numbers” in Memory

  4. program counter Stored Program Concept program fetch data load/store program A program A disk I/O data A program C program B program B data B processor hard disk main memory

  5. Stored Program Concept • Programs (instructions) are stored in memory as a stream of bits (numbers) • Indistinguishable from data • More than one program can reside in memory at the same time • Programs can be modified by the processor or I/O just as data can be modified • Instructions are fetched by the processor and decoded; they determine processor actions • Program Counter determines which instruction is fetched next

  6. Stored Program Concept • In fact, one of the great ideas in computer science is the idea that programs could be stored just as data is stored. • Before that, people envisioned the hardware running a fixed program, and data being stored in memory.

  7. …

  8. Addresses and Contents shown in Hex

  9. Number Systems • Actual machine code is in binary • O, 1 are high and low signals to hardware • Hex (base 16) is often used by humans (code, simulator, manuals, …) because: • 16 is a power of 2 (while 10 is not); mapping between hex and binary is easy • It’s more compact than binary • We can write, e.g., 0x90000008 in programs rather than 10010000000000000000000000001000

  10. Base 10 (Decimal) • Digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 (10 of them) • Example: • 3217 = (3103) + (2102) + (1101) + (7100) • A shorthand form we’ll also use: 103 102 101 100 3 2 1 7

  11. Numbers and Bases in General • Number Base B  B unique values per digit • Base 10: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} • Base 2: {0, 1} • Base 16: {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F} • (Unsigned) number representation • d31d30…d1d0 is a 32-digit non-negative number • Value = d31B31 + d30B30 + … + d1B1 + d0B0 • N-digit base B  BN unique values in N digits of base B

  12. Example: Base 2 (Binary) • Digits: 0, 1 (2 of them) • “Binary digit” = “Bit” • Example: • 11010two = (124) + (123) + (022) + (121) + (020) = 16 + 8 + 0 + 2 + 0 = 26ten • Choice for machine implementation! • 1 = on, 0 = off

  13. Base Conversion • Let’s do decimal-to-binary conversion: • Aten = dn-1dn-2…d1d0two • Given a base-10 number A, come up with n-digit binary number that has the same value! • X = the number • Let N be the largest power of 2 that fits into X • Put a 1 in that position • X = X – 2^N • Repeat until you are done!

  14. Base Conversion, cont’d • From binary to decimal • From decimal to binary • From binary to hexadecimal • From hexadecimal to binary • From decimal to hexadecimal? (more complicated; later)

  15. Base Conversion, cont’d • Binary to hex (base 16), or hex to binary base conversion: • Take 4 bits in binary and convert them into one hex digit and vice versa • For binary  hex: 4-bit groups, starting from the right • For hex  binary: translate each hex digit into 4 bits, starting from the right • Since binary notation tends to be long, hex notation is frequently used in assembly language (and in C programs). • More on binary number representation will be discussed when we study arithmetic

  16. Before moving on to chapter 2…. • We’ll mention some concepts in program performance, so you have ideas in mind • We’ll return to this material later in the course.

  17. Program Performance • Program performance is measured in terms of time! • Program execution time depends on: • Number of instructions executed to complete a job • How many clock cycles are needed to execute a single instruction • The length of the clock cycle (clock cycle time)

  18. Function block (made of circuits) Clock, Clock Cycle Time • Circuits in computers are “clocked” • At each clock rising (or falling) edge, some specified actions are done, usually within the next rising (or falling) edge • Instructions typically require more than one cycle to execute clock cycle time clock

  19. Program Performance • time = (# of clock cycles)  (clock cycle time) • # of clock cycles = (# of instructions executed)  (average cycles per instruction) • We’ll do specific calculations later • But now, let’s move on to Chapter 2

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