Chapitre 2 : Années cinquante

Transcription

1 Chapitre 2 : Années cinquante 1. Langage de programmation 2. Répertoire d instruction 3. Format d instruction 4. Modes d adressage 5. Type de langage machine 6. Technologie et logiciels 7. Premiers répertoire d instructions 8. Machine à accumulateur 9. Machine à registres Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 1

2 Langages de programmation Outil d écriture des programmes exécutables par ordinateur Langages de bas niveau : langages machine et langages d assemblage Langages de haut niveau ou évolués quelques instructions d un programme en langage machine ; transférer le contenu de l adresse 103 à A ; ajouter le contenu de A à B. quelque instructions d un programme en langage d assemblage. MOV A,103 ; transférer le contenu de l adresse 103 à A ADD A,B ; ajouter le contenu de A à B. Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 2

3 Caractéristiques des langages Langages de bas niveau étroitement lié à l ordinateur utilisé difficiles à lire et à écrire fortement exposés aux erreurs Langages de haut niveau indépendance par rapport à l ordinateur portabilité programmes facilement compréhensibles faciles à apprendre instructions proches de la langue naturelle Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 3

4 Programmation Programme en langage haut niveau.. A=A+B.... MOV A,103 ADD A,B.. Programme en langage d assemblage Compilateur Interpréteur Assembleur Programme en langage machine Ordinateur Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 4

5 Types d instruction machine Ensemble d instructions machine = répertoire d instructions Instruction de transfert de données entre la mémoire et les registre : MOVE, LOAD, STORE, Opération arithmétique ou logique : ADD, AND, Opération de contrôle d aiguillage : BR, JUMP, Instruction d entrée/sortie IN, OUT, Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 5

6 Format d instruction Façon avec laquelle les instructions sont stockées en mémoire ; transférer le contenu de l adresse 103 à A instruction Code d opération Adresse du registre A Adresse 103 Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 6

7 1 Influence of Technology and Software on Instruction Sets: Up to the dawn of IBM 360 Computer Science and Artificial Intelligence Laboratory M.I.T. Based on the material prepared by and Krste Asanovic

8 Importance of Technology L2-2 New technologies not only provide greater speed, size and reliability at lower cost, but more importantly these dictate the kinds of structures that can be considered and thus come to shape our whole view of what a computer is. Bell & Newell

9 6.823 L2-3 Technology is the dominant factor in computer design Technology Transistors Integrated circuits VLSI (initially) Laser disk, CD s Technology Core memories Magnetic tapes Disks Technology ROMs, RAMs VLSI Packaging Low Power Computers Computers Computers

10 But Software L2-4 As people write programs and use computers, our understanding of programming and program behavior improves. This has profound though slower impact on computer architecture Modern architects cannot avoid paying attention to software and compilation issues. Technology Software Computers

11 Computers in mid 50 s L2-5 Hardware was expensive Stores were small (1000 words) No resident system-software! Memory access time was 10 to 50 times slower than the processor cycle Instruction execution time was totally dominated by the memory reference time. The ability to design complex control circuits to execute an instruction was the central design concern as opposed to the speed of decoding or an ALU operation Programmer s view of the machine was inseparable from the actual hardware implementation

12 6.823 L2-6 Programmer s view of the machine IBM 650 A drum machine with 44 instructions Instruction: Load the contents of location 1234 into the distribution; put it also into the upper accumulator; set lower accumulator to zero; and then go to location 1009 for the next instruction. Good programmers optimized the placement of instructions on the drum to reduce latency!

13 6.823 L2-7 The Earliest Instruction Sets Single Accumulator - A carry-over from the calculators. LOAD STORE ADD SUB MUL DIV SHIFT LEFT SHIFT RIGHT JUMP JGE LOAD ADR STORE ADR x x x x x x x x x x AC M[x] M[x] (AC) AC (AC) + M[x] Involved a quotient register AC 2 (AC) PC x if (AC) 0 then PC x AC Extract address field(m[x]) Typically less than 2 dozen instructions!

14 Programming: Single Accumulator Machine L2-8 C i A i + B i, 1 i n A LOOP LOAD N B JGE DONE ADD ONE STORE N C F1 LOAD A F2 ADD B F3 STORE C N JUMP LOOP ONE DONE HLT -n 1 code How to modify the addresses A, B and C?

15 6.823 L2-9 Self-Modifying Code LOOP F1 F2 F3 DONE modify the program for the next iteration DONE LOAD JGE ADD STORE LOAD ADD STORE LOAD JUMP ADR ADD HLT STORE ADR LOAD ADR ADD STORE ADR LOAD ADR ADD STORE ADR JUMP HLT N DONE ONE N A B C F1 LOOP ONE F1 F2 ONE F2 F3 ONE F3 LOOP C i A i + B i, 1 i n Each iteration involves total bookkeeping instruction fetches operand fetches stores

16 Processor-Memory Bottleneck: Early Solutions L2-10 Fast local storage in the processor 8-16 registers as opposed to one accumulator Indexing capability to reduce book keeping instructions Complex instructions to reduce instruction fetches Memory Processor Compact instructions implicit address bits for operands, to reduce instruction fetches

17 Processor State L2-11 The information held in the processor at the end of an instruction to provide the processing context for the next instruction. Program Counter, Accumulator,... Programmer visible state of the processor (and memory) plays a central role in computer organization for both hardware and software: Software must make efficient use of it If the processing of an instruction can be interrupted then the hardware must save and restore the state in a transparent manner Programmer s machine model is a contract between the hardware and software

18 Index Registers Tom Kilburn, Manchester University, mid 50 s L2-12 One or more specialized registers to simplify address calculation Modify existing instructions LOAD x, IX AC M[x + (IX)] ADD x, IX AC (AC) + M[x + (IX)]... Add new instructions to manipulate index registers JZi x, IX if (IX)=0 then PC x else IX (IX) + 1 LOADi x, IX IX M[x] (truncated to fit IX)... Index registers have accumulator-like characteristics

19 6.823 L2-13 Using Index Registers LOADi -n, IX LOOP JZi DONE, IX LOAD LASTA, IX ADD LASTB, IX C i A i + B i, 1 i n STORE LASTC, IX JUMP LOOP LASTA DONE HALT Program does not modify itself Efficiency has improved dramatically (ops / iter) with index regs without index regs instruction fetch 5(2) 17 (14) operand fetch 2 10 (8) store 1 5 (4) Costs: Instructions are 1 to 2 bits longer Index registers with ALU-like circuitry Complex control A

20 6.823 L2-14 Indexing vs. Index Registers Suppose instead of registers, memory locations are used to implement index registers. LOAD x, IX Arithmetic operations on index registers can be performed by bringing the contents to the accumulator Most bookkeeping instructions will be avoided but each instruction will implicitly cause several fetches and stores complex control circuitry

21 Operations on Index Registers L2-15 To increment index register by k AC (IX) AC (AC) + k IX (AC) new instruction new instruction also the AC must be saved and restored. It may be better to increment IX directly INCi k, IX IX (IX) + k More instructions to manipulate index register STOREi x, IX M[x] (IX) (extended to fit a word)... IX begins to look like an accumulator several index registers several accumulators General Purpose Registers

22 6.823 L2-16 Support for Subroutine Calls Main Program call F a1 a2 F: Subroutine F call F b1 b2 return A special subroutine jump instruction M: JSR F F M + 1 and jump to F+1

23 Indirect Addressing and Subroutine Calls Indirect addressing LOAD (x) means AC M[M[x]]... Caller Events: M JSR F Execute M arg Execute S1 result Execute S2 M+3 Execute S3 F F+1 S1 S2 Subroutine M+1 M+2 M+3 LOAD (F) inc F STORE(F) inc F L2-17 fetch arg store result Indirect addressing almost eliminates the need to write self-modifying code (location F still needs to be modified) S3 JUMP (F) Problems with recursive procedure calls

24 Recursive Procedure Calls and Reentrant Codes L2-18 Indirect Addressing through a register LOAD R 1, (R 2 ) Load register R 1 with the contents of the word whose address is contained in register R 2 registers PC SP memory Pure Code Data Stack

25 6.823 L2-19 Evolution of Addressing Modes 1. Single accumulator, absolute address LOAD x 2. Single accumulator, index registers LOAD x, IX 3. Indirection LOAD (x) 4. Multiple accumulators, index registers, indirection LOAD R, IX, x or LOAD R, IX, (x) the meaning? R M[M[x] + (IX)] or R M[M[x + (IX)]] 5. Indirect through registers LOAD R I, (R J ) 6. The works LOAD R I, R J, (R K ) R J = index, R K = base addr

26 6.823 L2-20 Variety of Instruction Formats Two address formats: the destination is same as one of the operand sources (Reg Reg) to Reg R I (R I ) + (R J ) (Reg Mem) to Reg (R I ) + M[x] x can be specified directly or via a register effective address calculation for x could include indexing, indirection,... Three address formats: One destination and up to two operand sources per instruction (Reg x Reg) to Reg R I (R J ) + (R K ) (Reg x Mem) to Reg R I (R J ) + M[x] R I

27 6.823 L2-21 More Instruction Formats Zero address formats: operands on a stack add load M[sp-1] M[sp] + M[sp-1] M[sp] M[M[sp]] Stack can be in registers or in memory (usually top of stack cached in registers) One address formats: Accumulator machines Accumulator is always other implicit operand Many different formats are possible!

28 6.823 L2-22 Data Formats and Memory Addresses Data formats: Bytes, Half words, words and double words Some issues Byte addressing Big Endian vs. Little Endian Word alignment Suppose the memory is organized in 32-bit words. Can a word address begin only at 0, 4, 8,...?

29 Some Problems L2-23 Should all addressing modes be provided for every operand? regular vs. irregular instruction formats Separate instructions to manipulate Accumulators, Index registers, Base registers large number of instructions Instructions contained implicit memory references -- several contained more than one very complex control

30 6.823 L2-24 Compatibility Problem at IBM By early 60 s, IBM had 4 incompatible lines of computers! Each system had its own Instruction set I/O system and Secondary Storage: magnetic tapes, drums and disks assemblers, compilers, libraries,... market niche business, scientific, real time,... IBM 360

31 IBM 360 : Design Premises Amdahl, Blaauw and Brooks, L2-25 The design must lend itself to growth and successor machines General method for connecting I/O devices Total performance - answers per month rather than bits per microsecond programming aids Machine must be capable of supervising itself without manual intervention Built-in hardware fault checking and locating aids to reduce down time Simple to assemble systems with redundant I/O devices, memories etc. for fault tolerance Some problems required floating point words larger than 36 bits

32 IBM 360: A General-Purpose Register (GPR) Machine L2-26 Processor State 16 General-Purpose 32-bit Registers may be used as index and base register Register 0 has some special properties 4 Floating Point 64-bit Registers A Program Status Word (PSW) PC, Condition codes, Control flags A 32-bit machine with 24-bit addresses No instruction contains a 24-bit address! Data Formats 8-bit bytes, 16-bit half-words, 32-bit words, 64-bit double-words

33 6.823 L2-27 IBM 360: Implementation Model Model 70 Storage 8K - 64 KB 256K KB Datapath 8-bit 64-bit Circuit Delay 30 nsec/level 5 nsec/level Local Store Main Store Transistor Registers Control Store Read only 1µsec Conventional circuits IBM 360 instruction set architecture completely hid the underlying technological differences between various models. With minor modifications it survives till today

34 6.823 L2-28 IBM S/390 z900 Microprocessor 64-bit virtual addressing first 64-bit S/390 design (original S/360 was 24-bit, and S/370 was 31-bit extension) 1.1 GHz clock rate (announced ISSCC 2001) 0.18µm CMOS, 7 layers copper wiring 770MHz systems shipped in 2000 Single-issue 7-stage CISC pipeline Redundant datapaths every instruction performed in two parallel datapaths and results compared 256KB L1 I-cache, 256KB L1 D-cache on-chip 20 CPUs + 32MB L2 cache per Multi-Chip Module Water cooled to 10 o C junction temp

35 6.823 L2-29 What makes a good instruction set? One that provides a simple software interface yet allows simple, fast, efficient hardware implementations but across 25+ year time frame Example of difficulties: Current machines have register files with more storage than entire main memory of early machines! On-chip test circuitry in current machines has hundreds of times more transistors than entire early computers!

36 6.823 L2-30 Full Employment for Architects Good news: Ideal instruction set changes continually Technology allows larger CPUs over time Technology constraints change (e.g., now it is power) Compiler technology improves (e.g., register allocation) Programming styles change (assembly, HLL, object-oriented, ) Applications change (e.g., multimedia,...) Bad news: Software compatibility imposes huge damping coefficient on instruction set innovation Software investment dwarfs hardware investment Innovate at microarchitecture level, below the ISA level (this is what most computer architects do) New instruction set can only be justified by new large market and technological advantage Network processors Multimedia processors DSP s

37 Modes d adressage chemin à suivre pour obtenir l adresse effective Mode direct ou absolu : MOVE R1, R2 ; R1 (R2) MOVE R1, 405 ; R1 (405) Mode immédiat : MOVI R1, 405 ; R1 405 MOVI 103, 405 ; Mode indirect : MOVE ; R1 ((100)) Mode indexé : MOVE R1, 17(R2) ; R1 (10 + (R2)) MOVE 1, Table(R2) ; 1 (Table + (R2)) Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 7

38 Types de langage machine (1/2) Considérons l instruction : A= B + C Machine à plusieurs opérandes (Vax 11) : ADDW3 B,C,A ; A (B) + (C) Machine à deux opérandes (PDP 11) : MOVE B,A ; A (B) ADD C,A ; A (B) + (C) Machine à un opérande (Vax 11) LDM B ; Charger B dans l accumulateur ADD C ; Ajouter C a l accumulateur STM A ; Stocker l accumulateur dans A Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 8

39 Types de langage machine (2/2) Considérons l instruction : A= B + C Machine à registres (Cyber 170) EA1 B ; X1 (B) EA2 C ; X2 (C) IX6 X1 + X2 ; X6 (X1) + (X2) SA6 A ; A (X6) Machine à registres (HP 3000) LOAD B ; mettre B dans la pile LOAD C ; mettre C dans la pile ADD ; ajouter les 2 élément au dessus de la pile et mettre ; le résultat sur la pile STORE A ; 1 (Table + (R2)) Architecture des ordinateurs, M. Eleuldj, EMI, Février 2008 Ch.II. 9