micro-programmed control (kontroltermikroprogram) · 2010. 6. 8. · microsoft powerpoint -...
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Organisasi Komputer I I
Micro-programmed Control
(Kontrol Termikroprogram)
Organisasi Unit Kontrol
Micro-programmed Control
Use sequences of instructions (see earlier notes) to control complex operationsCalled micro-programming or firmware
CONTROL UNIT MICROPROGRAMMED
Terbagi 2 yaitu :1. Control Vertikal
Jenis implementasi dimana signal kontrol di kode ke dalam pada bit , kemudian digunakan setelah dikode.
2. Control HorizontalControl dimana setiap bit kontrol mengatur 1 operasi gate ataumesin.
KOMPONEN-KOMPONEN POKOK CONTROL UNIT
MICROPROGRAMMED
1. Instruction Register Menyimpan instruksi register mesin yang dijalankan.
2. Control Store berisi microprogrammedUntuk semua instruksi mesin.Untuk startup mesin.Untuk memprosesan interupt
3. Address Computing CircuitingMenentukan alamat Control Store dari mikroinstruksiberikutnya yang akan dijalankan.
4. Microprogrammed CounterMenyimpan alamat dari mikroinstruksi berikutnya.
5. Microinstruction BufferMenyimpan mikroinstruksi tersebut selama dieksekusi.
6. Microinstruction DecoderMenghasilkan dan mengeluarkan mikroorder yang didasarkan pada mikroinstruksi dan opcode instruksiyang akan dijalankan
Implementat ion (1)
All the control unit does is generate a set of control signalsEach control signal is on or offRepresent each control signal by a bitHave a control word for each micro-operationHave a sequence of control words for each machine code instructionAdd an address to specify the next micro-instruction, depending on conditions
Implementat ion (2)
Today s large microprocessorMany instructions and associated register-level hardwareMany control points to be manipulated
This results in control memory thatContains a large number of words
co-responding to the number of instructions to be executed
Has a wide word width Due to the large number of control points to be manipulated
Micro-program Word Length
Based on 3 factorsMaximum number of simultaneous micro-operations supportedThe way control information is represented or encodedThe way in which the next micro-instruction address is specified
Micro-instruct ion Types
Each micro-instruction specifies single (or few) micro-operations to be performed
(vertical micro-programming)
Each micro-instruction specifies many different micro-operations to be performed in parallel
(horizontal micro-programming)
Vert ical Micro-programming
Width is narrown control signals encoded into log2 n bitsLimited ability to express parallelismConsiderable encoding of control information requires external memory word decoder to identify the exact control line being manipulated
Horizontal Micro-programming
Wide memory wordHigh degree of parallel operations possibleLittle encoding of control information
Typical Microinstruct ion Formats
Compromise
Divide control signals into disjoint groupsImplement each group as separate field in memory wordSupports reasonable levels of parallelism without too much complexity
Organizat ion ofControl Memory
Control Unit
Control Unit Funct ion
Sequence login unit issues read commandWord specified in control address register is read into control buffer registerControl buffer register contents generates control signals and next address informationSequence login loads new address into control buffer register based on next address information from control buffer register and ALU flags
Next Address Decision
Depending on ALU flags and control buffer register
Get next instructionAdd 1 to control address register
Jump to new routine based on jump microinstructionLoad address field of control buffer register into control address register
Jump to machine instruction routineLoad control address register based on opcode in IR
Functioning of MicroprogrammedControl Unit
Wilkes Control
1951Matrix partially filled with diodesDuring cycle, one row activated
Generates signals where diode presentFirst part of row generates controlSecond generates address for next cycle
Wilkes's Microprogrammed Control Unit
Advantages and Disadvantages of Microprogramming
Simplifies design of control unitCheaperLess error-prone
Slower
Tasks Done By MicroprogrammedControl Unit
Microinstruction sequencingMicroinstruction executionMust consider both together
Design Considerat ions
Size of microinstructionsAddress generation time
Determined by instruction registerOnce per cycle, after instruction is fetched
Next sequential addressCommon in most designed
BranchesBoth conditional and unconditional
Sequencing Techniques
Based on current microinstruction, condition flags, contents of IR, control memory address must be generatedBased on format of address information
Two address fieldsSingle address fieldVariable format
Branch Control Logic: Tw o Address Fields
Branch ControlLogic: Single Address Field
Branch Control Logic: Variable Format
Address Generat ion
Residual controlConditional branch
AdditionUnconditional Branch
MappingTwo-field
ImplicitExplicit
Execution
The cycle is the basic eventEach cycle is made up of two events
FetchDetermined by generation of microinstruction address
Execute
Execute
Effect is to generate control signalsSome control points internal to processorRest go to external control bus or other interface
Control Unit Organizat ion
A Taxonomy of Microinstruct ions
Vertical/horizontalPacked/unpackedHard/soft microprogrammingDirect/indirect encoding
Improvements over Wilkes
Wilkes had each bit directly produced a control signal or directly produced one bit of next addressMore complex address sequencing schemes,using fewer microinstruction bits, are possibleRequire more complex sequencing logic moduleControl word bits can be saved by encoding and subsequently decoding control information
How to EncodeK different internal and external control signals Wilkes s:
K bits dedicated 2K control signals during any instruction cycle
Not all usedTwo sources cannot be gated to same destinationRegister cannot be source and destinationOnly one pattern presented to ALU at a timeOnly one pattern presented to external control bus at a time
Require Q < 2K which can be encoded with log2Q < K bitsNot done
As difficult to program as pure decoded (Wilkes) schemeRequires complex slow control logic module
CompromisesMore bits than necessary usedSome combinations that are physically allowable are not possible to encode
Specific Encoding Techniques
Microinstruction organized as set of fieldsEach field contains codeActivates one or more control signalsOrganize format into independent fields
Field depicts set of actions (pattern of control signals) Actions from different fields can occur simultaneously
Alternative actions that can be specified by a field are mutually exclusive
Only one action specified for field could occur at a time
Microinstruct ion EncodingDirect Encoding
Microinstruct ion EncodingIndirect Encoding