Instructions and Addressing (cont’d.). Index addressing (1) opcode Reg index instruction operand...

Instructions and Addressing (cont’d.)

Index addressing (1)

opcode Reg index

instruction

operand

memoryor

registers

operand

+

registers

Index addressing (2)

• Advantages:- Allows specification of fixed offset to operand

address

• Disadvantages:- Extra addition to operand address

• Notation: ADD X(R1),R3 (X=number)• Meaning: [R3] [R3] + M([R1] + X)

Example index addressing

NE

Program with index addressing

programloop

sexagesalary

nEmpoyee IDsexagesalaryEmpoyee ID

L

Move #E,R0

Move N,R1

Clear R2

Add 8(R0),R2

Add #16,R0

Decrement R1

Branch>0 L

Div R1,R2

Move R2,Sum

Move N,R1

0(R0) 4(R0) 8(R0)12(R0)16(R0)20(R0)

Q1: What does this program do?

Additional modes

• Some computers have auto-increment (decrement instructions)

• Example: (R0)+• Meaning .. M(R0)..; [R0] [R0]+1• Example: -(R0)• Meaning [R0] [R0]-1; .. M(R0)..

6

Additional Instructions

• Logic instructions- Not R0; invert all bits in R0- And #$FF000000,R0; AND with bit string

• Shift and rotate instructions- Many variants for different purposes

7

Logical shifts

CR00

before:

after:

0

1

0 0 01 1 1 . . . 11

0 0 1 1 1 000

Logical shift leftLShiftL #2,R0

C R0 0

before:

after:

0

1

0 0 01 1 1 . . . 11

1 10 . . . 00101

. . .

used in bit Packing

virtual: 0 1 11 1 0 . . 010.

LShiftL #2,R0

LShiftL #1,R0

Logical shift rightLShiftR #2,R0

00 00 1 1 . . 101 .virtual:

LShiftR #2,R0

LShiftR #1,R0

8

Arithmetic shifts

C

before:

after:

0

1

1 1 00 0 1 . . . 01

1 1 0 0 1 011

R0

. . .01 11 0 0 . . 101 .virtual:

AShiftR #2,R0

AShiftR #1,R0

Arithmetic shift right (signed shift)AShiftR #2,R0

Q1: AShiftR by n bits is equivalent to division by 2n for numbers in 2C or 1C?Q2: Rounding negative number shifts towards 0 or -infinity?T

ough

qu

estio

ns

9

Rotate

Rotate left w/o CarryRotateL #2,R0

C R0

before:

after:

0

1

0 0 01 1 1 . . . 11

1 10 . . . 10101

virtual: 0 1 11 1 0 . . 010.

RotateL #2,R0

RotateL #1,R0

Rotate left w/ CarryRotateLC #2,R0

C R0

before:

after:

0

1

0 0 01 1 1 . . . 11

1 10 . . . 00101

virtual: 0 1 11 1 0 . . 010.

RotateLC #2,R0

RotateLC #1,R0

10

Assemblershttp://www.pds.ewi.tudelft.nl/~iosup/Courses/2011_ti1400_5.ppt

Done so far…

Circuit Design

Digital logicMemory elementsOther building blocks (Multiplexer,Decoder)Finite State Machines

Lecture 1

Programmable Devices

Memory organizationProgram sequencingvon Neumann archi.Instruction levels

Lecture 2

History of Computing(1642-2011)

Why Computer Organization Matters?Lecture 0

ComputersLectures 3,4

Data representation, conversion, and op.Instruction representation and use

Problem: How to Program Computers?

Circuit Design

Digital logicMemory elementsOther building blocks (Multiplexer,Decoder)Finite State Machines

Lecture 1

Programmable Devices

Memory organizationProgram sequencingvon Neumann archi.Instruction levels

Lecture 2

Why Computer Organization Matters?Lecture 0

ComputersLectures 3,4

Data representation, conversion, and op.Instruction representation and use

TU-DelftTI1400/11-PDS

13

Program Creation and Execution Flow

editor

type sourceprogram

Source in ASCII

linker/loaderlink/load

memory imagerun input/output

machine 2

assembler listingtranslate

Source andObject code+error messages

object code

machine 1

Three levels of instructions

fetch/executeimplementation

program executionin hardware

high level programminglanguage

program expressed in ahigh-level language

translation

instruction set program expressed as a series of instructions

direct implementationAssembler

C/C++, Java, …

15

Instructions and Addressing

1. Introduction2. Assembler: What and Why?3. Assembler Statements and Structure4. The Stack5. Subroutines6. Architectures: CISC and RISC


16

Why assembler? [1/2]

• Assembler is a symbolic notation for machine language

• It improves readability (vs machine code):- Assembler: Move R0,SUM - Machine code: 0010 1101 1001 0001 (16 bits)


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Why assembler ? [2/2]

• Speed of programs in critical applications• Access to all hardware resources of the

machine• Target for compilers

Source: http://www.cs.berkeley.edu/~volkov/cs267.sp09/hw1/results/

Lecture 0

Q: Where to get ISA references?

• Manufacturer’s documentation

• Third-party manuals (ATTN: may be incorrect)

Q: Does each processor have its own machine language (instruction set)?• Shared across generations and even

competitors

www.eng.ucy.ac.cy/theocharides/Courses/ECE656/ia-32.pdf

developer.download.nvidia.com/compute/cuda/3_1/toolkit/docs/ptx_isa_2.1.pdf

1982

1985

1989

1993

1995

Intel

AMD

Cyrix

…

NVIDIA

Q: Are similar instructions identical on different platforms?• Often, they are not

NVIDIAIntel

AMD

Cyrix


21

Machine Language [1/4]

• Is Machine language difficult to learn?- That holds for every unknown language. Machine

language is more difficult because you have to work with the specifically defined micro instruction set.

• Is Machine language difficult to read and to understand?- Of course, if you do not know the language;

however, assembler is more difficult to read and understand than a High Level Language (HLL).


22


• Is Machine language difficult to write?- Often HLL languages use libraries to make programming

simpler. Machine language programmers often start from scratch. However, full performance may require machine language implementation (or a smart/expensive compiler)

• Machine language programming is time consuming- One estimates that the time for coding a program is only

30% of the total development time.


23


• Compilers make machine language superfluous- A good machine language program often looks very

different from a compiler generated program. Generally, a C program will win over a hand-made assembly program (unless you’re Michael Abrash … or a student at TU Delft)

- Assembler still heavily used for hot/optimized functions (esp. scientific codes), real-time platforms, embedded systems, …


24


• Is Machine language difficult to maintain?- Maintainable programs are not specifically dependent on

the language they are written in, but more on the way they are contructed

• Is Machine language difficult to debug?- Often debuggers output both the HLL and the machine

language, and the error can only be found in the generated machine language


25

Case-in-Point

• Universele Brander Automaat (UBA)


26

Case

Universele Brander AutomaatKlant: Nefit Fasto B.V.Markt: HVAC (AirCo)Ontwikkelen (1990) en produceren (100k/jaar) van de UBA universele brander- automaat voor Nefit Fasto voorzien van een bipolaire Application-Specific Integrated Circuit (ASIC).Eerste product met een universeel karakter, die een fail-safe approval heeft.


27

Case

6 schakel ingangen8 analoge ingangen3 schakeluitgangen3 modulerende uitgangen2 draads communicatie bus

Externe KIM module aansluiting met 178 bytes config settings

230V , Pump and Fan

ASIC and micro-Computer

Ignition

Universele Brander Automaat


28

UBA software opbouw

HWIO

Application

1 Kbyte

15 Kbyte

C- language


29

UBA micro computer

HWIO

1 Kbytes

MC68HC05B16

24 I/O bi-directional8 A/D analogue inputs2 TCAP input timers2 TCMP output compare2 PWM D/A outputs1 SCI serial output 1 COP watchdog256 bytes RAM256 bytes EEPROM16 Kbytes (EP)ROM


30

UBA PuR After Power up Reset special routine[ see also The Zen of Diagnostics, http://www.ganssle.com/articles/adiags1.htm ]

- all instruction set in test routine- 16-bit CRC (99,98% data integrity)

- Walking A0 and 05 RAM test (pattern sensitivity)- Check on A/D (converter linearity)

- Main loop partitioned in modules- Module check in each phase

- Acknowledge module check by pulse to ASIC (350ms)- Interrupt program termination check by pulse to ASIC (20ms)


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UBA Assembly

• Check instruction set- Test of each opcode over and over

again- Emergency stop at fault detection- Not possible in “C”

• Check memory- As part of the program- Emergency stop at fault detection- Difficult in “C”

• Better control on application- Compiler generated code must be

checked for correctness.


32




33

Assembler Statements

• Declarations- no code generation- memory reservation- symbolic data declarations- where to start the code execution

• Executable statements- are translated to real machine instructions

(often, one-to-one)


34

Data declarations

S EQU 200

ORIGIN 201

N DATA 300

N1 RESERVE 300

ORIGIN 100

Label operation operand


35

Program

START Move N,R1

Addr operation operand

Move #N1,R2

Clear R0

LOOP Add (R2),R0

Incr R2

Decr R1

Branch>0 LOOP

Move R0,S

Return

End START


36

Memory lay-out

Move N,R1100

..... 102

103

104

105

106

107

101

..... ..... ..... ..... Branch >0

200

300 202

203

501

201

..... ..... ..... .....

Nn

S

N

N1


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Structure assembler [1/3]

• Assembler is hardly more than substitution- substitute 0001 for Move- substitute 0000 0000 0000 0101 for #5

• Assembler is level above machine language• Assembler languages for different

architectures are alike, but not identical


38


Assembler programs contain three kind of quantities:

• Absolute:- opcodes, contants: can be directly translated

• Relative:- addresses of instructions which are dependent of

final memory location

• Extern:- call to subroutines


39


• Literals: constants in programs• Some assemblers act as if literals are

immediate operands• Example:

Load #1

is equivalent to:Load One

...

One: 1


40

Number notation

• Numbers can be represented using various formats:

ADD #93,R1

orADD #%01011101,R1

orADD #$5D,R1


41




The StackMain idea

- (Large?) Memory space used to store program data- Items are added to the stack through a PUSH operation- Items are removed from the stack through a POP

operation

Details- Often, a stack is a contiguous array of memory

locations- Often, any number of stacks can be set up by a

program- Often, only one stack can be used at a time

(changing the active stack possible at any time)Q1: Why use stacks?

Q2: Implications?


43

Stack registers

SPPC

CPU

MainMemory

Stack Pointer


44

Stack operations

70

300

20

10

60

SP

0

1


45

Push

70

300

20

10

60

SP

Subtract #4,SPMove R0,(SP)

80

0

1

80 R0

or:Move R0,-(SP)


46

Pop

70

300

20

10

60

SP

Move (SP),R0Add #4,SP80

0

1

70 R0

or:Move (SP)+,R0


47




48

Subroutines

• More structure in programs• Mimics procedure and function calls in

High Level programming Languages (HLL)


49

Calling mechanism

Call SUB

next instr.

200

204

................1000

................

RTS

204

204

PC Link

PC Link

50

Question

Is a Link register sufficient ?


51

Subroutine nesting

• For nesting of subroutines return address in link register must be stored

• Can be implemented by using stacks


52

Subroutine stack

204

PC Link

Move Link, -(SP)

Stack

......

Move (SP)+, Link

RTS

subroutine


53

Parameter passing (1)

• Through registers- fast- limited number of parameters- caller and callee must know where parameters

are placed

• Example:Move A,R0 Sub: Move R0,CCall Sub ......

RTS


54


• Through memory- very flexible- slower than through registers

• Often implemented through Stack Pointer• Parameters are pushed on stack before

calling subroutine• Results are popped from stack after return• Subroutine needs registers


55


Move #List, -(SP)Move N, -(SP)Call LISTADDMove 4(SP), SUMAdd #8, SP

calling subroutine

Stack

SP


56



LISTSP

calling subroutine

Stack


57



n

LIST

SP

calling subroutine

Stack


58


Move #List, -(SP)Move N, -(SP)Call LISTADDMove 4(SP), SUMAdd #8, SP Return

n

LIST

SP

calling subroutine

Stack


59



n

sum

SP

calling subroutine

Stack


60



SP

calling subroutine

Stack


61


[R0]

Return

n

LIST

Stack frameLISTADD Move R0, -(SP)...Move 16(SP), R1Move 20(SP), R2Clear R0

LOOP Add (R2), R0Decr R1Incr R2Branch>0 LOOPMove R0, 20(SP)Move (SP)+, R2.....Return

Subroutine

SP


62


[R2]

[R1]

[R0]

Return

n

LIST



Subroutine

SP


63


[R2]

[R1]

[R0]

Return

n

sum



Subroutine

SP 0(SP)

4(SP)

8(SP)

12(SP)

16(SP)

20(SP)20(SP)


64

Parameter passing(4)

[R1]

[R0]

Return

n

sum



Subroutine

SP


65


Return

n

sum



Subroutine

SP


66

Frame Pointer

SP(stack pointer)

FP(frame pointer)

saved [R1]

saved [R0]

Stackframefor

calledsubroutine

Return address

localvar3

localvar2

localvar1

saved [FP]

Old ToS

param2

param1

param3

param4

(top-of-stack)

Access of local variablesof Subroutinethrough IndexAddressing on FP


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Re-entrancy

• Subroutines can be called more than once- Recursion: subroutine calls itself- Sub A calls Sub B, which in turn calls Sub A- Multiple callers “at the same time”

• Special measures for re-entrancy- No change of instructions- Each caller must have its own copy of data- Use stack(s)


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69

CISC characteristics

• Complex Instruction Set• Traditional architectures• Powerful instructions

- Complex operations- Many instructions

• Memory to memory operations• Programs often use stacks• Examples 68xxx and 80xxx architectures• The Pentium architecture

Memory CPU


70

RISC characteristics

• Reduced Instruction Set• Small number of instructions• Load/Store from memory• Operations between registers• Large register sets• Example PowerPC architecture

Memory CPU


Pro CISC

• Easier to program• Reduced code size• Complexity in hardware not in software

- HLL support in hardware

• (Politics) Legacy- CISCs are in all our PCs and servers

See also: http://arstechnica.com/cpu/4q99/risc-cisc/rvc-5.html


Con CISC

• Instruction encoding complex• Variable number of cycles to load instruction

- IA-32 instructions can be 1—17 bytes long

• Many instructions too specific, thus not used• May be slow

- Stacks are in main memory, registers are near processor

• May consume more energy- Not in embedded systems, portable devices, …


Frequency of Instruction Use

Frequency of Use(logscale)

Instruction Rank

Source: http://www.eng.ucy.ac.cy/theocharides/Courses/ECE656/ia-32.pdf

50% code just 3 instructions (mov, call, jmp)

99% code under 50 instructions

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