33、representations, sequence control and logic representation, and control implementation = all may be determined indep.Initial Rep. Finite State Diagram Microprogram Sequencing Explicit Next State Microprogram Control Function Counter + Dispatch ROMs Logic Rep. Logic Equations Truth Tables Implementat 。

34、ion PLA ROM,Controller Design: An Overview,hardwired control,microprogrammed control,Multicycle Design-51,Control is the hard part of processor design Datapath is fairly regular and well-organized Memory is highly regular Control is irregular and global But, the state diagrams that define the contro 。

35、ller for an instruction set processor are highly structured Use this structure toconstruct a simple“microsequencer” Control reduces toprogramming thissimple device = microprogramming,sequencer control,datapath control,micro-PC,sequencer,microinstruction,Microprogram,control signals,Multicycle Design 。

36、-52,Microinstruction,Control signals : Think of the set of control signals that must be asserted in a state as an instruction Executing a microinstruction has the effect of asserting the control signal specified by the microinstruction Sequencing What microinstruction should be executed next ? Execu 。

37、te sequentially (next state unconditionally) Branch (next state also depends on inputs) A microprogram is a sequence of microinstructions executing a program flow chart (finite state machine,Multicycle Design-53,1) Start with a list of control signals 2) Group signals together that make sense (vs. r 。

38、andom): called fields 3) Places fields in some logical order (e.g., ALU operation B = Regrt;
Write ALURegrd = ALUout Write MDRRegrt = MDR MemoryRead PCIR (MDR) = memPCRead ALUMDR = memALUoutWrite ALUmemALUout = BPC writeALUPC = ALU outputALUout-cond.IF ALU zero then PC = ALUoutjump addr.PC = PCSourc 。

39、eSequencingSeqGo to sequential microinstructionFetchGo to the first microinstructionDispatch 1Dispatch using ROM1 Dispatch 2Dispatch using ROM2,Control Signals,Multicycle Design-57,The Microprogram,Multicycle Design-58,The Controller,Fig. C.4.6,Multicycle Design-59,The Dispatch ROMs,Fig. C.5.2,Rform 。

40、at1,JUMP1,BEQ1,Mem1,Mem1,LW2,SW2,Multicycle Design-60,Our Plan: Using ROM,Multicycle Design-61,Main Memory,execution unit,control memory,CPU,ADD SUB AND,DATA,.,User program plus Data this can change,AND microsequence e.g., Fetch Calc Operand Addr Fetch Operand(s) Calculate Save Answer(s,one of these 。

41、 is mapped into one of these,Microinstruction Interpretation,Multicycle Design-62,Microprogramming Using ROM : Pros and Cons,Ease of design Flexibility Each to adapt to changes in organization, timing, technology Can make changes late in design cycle, or even in the field Generality Implement multip 。

42、le inst. sets on same machine Can tailor instruction set to application Can implement very powerful instruction sets (just more control memory) Compatibility Many organizations, same instruction set Costly to implement and Slow,Multicycle Design-63,5) Microinstruction Encoding,Fig. C.4.5,Bits 7-13 c 。

43、an be encoded to 3 bits because there are only 7 patterns of the control word,Multicycle Design-64,Minimal vs. Maximal Encoding,Minimal (Horizontal ): + more control over the potential parallelism of operations in the datapath - uses up lots of control store Maximal (Vertical): + uses less number of 。

44、 control store - extra level of decoding may slow the machine down,Multicycle Design-65,Control is specified by a finite state diagram Specialized state-diagrams easily captured by microsequencer simple increment and “branch” fields datapath control fields Control can also be specified by microprogr 。

45、amming Control is more complicated with: complex instruction sets restricted datapaths Simple instruction set and powerful datapath = simple control could reduce hardware Or go for speed = many instructions at once,Summary of Control,Multicycle Design-66,Outline,Designing a processor Building the da 。

46、tapath A single-cycle implementation A multicycle implementation Multicycle datapath Multicycle execution steps Multicycle control Microprogramming: simplifying control Exceptions,Multicycle Design-67,Exceptions,User Program,System Exception Handler,Exception,return from exception,Normal control flo 。

47、w: sequential, jumps, branches, calls, returns Exception = unprogrammed control transfer system takes action to handle the exception must record address of the offending instruction should know cause and transfer to proper handler if returns to user, must save & restore user state,Multicycle Design- 。

48、68,By providing two modes of execution (user/system), computer may manage itself OS is a special program that runs in the privileged system mode and has access to all of the resources of the computer Presents “virtual resources” to each user that are more convenient than the physical resources files 。

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标题：CS4100|CS4100： 计算机结构( 三 )