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Berkeley COMPSCI 152 - Lecture 4 – Timing

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CS 152 L03 Testing Processors () UC Regents Fall 2004 © UCB2004-09-07 Dave Patterson(www.cs.berkeley.edu/~patterson)John Lazzaro (www.cs.berkeley.edu/~lazzaro)www-inst.eecs.berkeley.edu/~cs152/CS152 – Computer Architecture andEngineeringLecture 4 – Timing1CS 152 L03 Testing Processors () UC Regents Fall 2004 © UCBLast Time: Test plan for your projectcomplete processor testingTop-downtestingBottom-uptestingunit testingprocessortestingwithself-checksWhich testing types are good for each epoch?processorassemblycompletecorrectlyexecutes singleinstructionscorrectlyexecutes shortprogramsTimeEpoch 1 Epoch 2Epoch 3 Epoch 4unit testingearlymultiunit testinglatermulti-unit testingprocessortestingwithself-checksmulti-unit testingunit testingdiagnosticscomplete processor testingverificationprocessortestingwithself-checksdiagnosticsprocessortestingwithself-checksmulti-unit testingunit testingdiagnostics2CS 152 L03 Testing Processors () UC Regents Fall 2004 © UCBOutline - TimingTeam networking break!A clocked logic circuit primerMore clocked logic circuits3CS 152 L03 Testing Processors () UC Regents Fall 2004 © UCB1600 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 36, NO. 11, NOVEMBER 2001Fig. 1. Process SEM cross section.The process was raised from [1] to limit standby power.Circuit design and architectural pipelining ensure low voltageperformance and functionality. To further limit standby currentin handheld ASSPs, a longer poly target takes advantage of theversus dependence and source-to-body bias is usedto electrically limit transistor in standby mode. All corenMOS and pMOS transistors utilize separate source and bulkconnections to support this. The process includes cobalt disili-cide gates and diffusions. Low source and drain capacitance, aswell as 3-nm gate-oxide thickness, allow high performance andlow-voltage operation.III. ARCHITECTUREThe microprocessor contains 32-kB instruction and datacaches as well as an eight-entry coalescing writeback buffer.The instruction and data cache fill buffers have two and fourentries, respectively. The data cache supports hit-under-missoperation and lines may be locked to allow SRAM-like oper-ation. Thirty-two-entry fully associative translation lookasidebuffers (TLBs) that support multiple page sizes are providedfor both caches. TLB entries may also be locked. A 128-entrybranch target buffer improves branch performance a pipelinedeeper than earlier high-performance ARM designs [2], [3].A. Pipeline OrganizationTo obtain high performance, the microprocessor core utilizesa simple scalar pipeline and a high-frequency clock. In additionto avoiding the potential power waste of a superscalar approach,functional design and validation complexity is decreased at theexpense of circuit design effort. To avoid circuit design issues,the pipeline partitioning balances the workload and ensures thatno one pipeline stage is tight. The main integer pipeline is sevenstages, memory operations follow an eight-stage pipeline, andwhen operating in thumb mode an extra pipe stage is insertedafter the last fetch stage to convert thumb instructions into ARMinstructions. Since thumb mode instructions [11] are 16 b, twoinstructions are fetched in parallel while executing thumb in-structions. A simplified diagram of the processor pipeline isFig. 2. Microprocessor pipeline organization.shown in Fig. 2, where the state boundaries are indicated bygray. Features that allow the microarchitecture to achieve highspeed are as follows.The shifter and ALU reside in separate stages. The ARM in-struction set allows a shift followed by an ALU operation in asingle instruction. Previous implementations limited frequencyby having the shift and ALU in a single stage. Splitting this op-eration reduces the critical ALU bypass path by approximately1/3. The extra pipeline hazard introduced when an instruction isimmediately followed by one requiring that the result be shiftedis infrequent.Decoupled Instruction Fetch. A two-instruction deep queue isimplemented between the second fetch and instruction decodepipe stages. This allows stalls generated later in the pipe to bedeferred by one or more cycles in the earlier pipe stages, therebyallowing instruction fetches to proceed when the pipe is stalled,and also relieves stall speed paths in the instruction fetch andbranch prediction units.Deferred register dependency stalls. While register depen-dencies are checked in the RF stage, stalls due to these hazardsare deferred until the X1 stage. All the necessary operands arethen captured from result-forwarding busses as the results arereturned to the register file.One of the major goals of the design was to minimize the en-ergy consumed to complete a given task. Conventional wisdomhas been that shorter pipelines are more efficient due to re-Architects draw blocks ...Circuit designers draw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ogic is where they meet. 4CS 152 L02 Design as a Team Sport () UC Regents Fall 2004 © UCBArchitects reach logic top-down ...Next State Combinational Logicnext_Gnext_R next_YR G YChangeRstwire next_R, next_Y, next_G;assign next_R = rst ? 1’b1 : (change ? Y : R); assign next_Y = rst ? 1’b0 : (change ? G : Y);assign next_G = rst ? 1’b0 : (change ? R : G); Is this structural Verilog?5CS 152 L02 Design as a Team Sport () UC Regents Fall 2004 © UCB1/28/04 ©UCB Spring 2004CS152 / Kubiatowicz Lec3.33Basic Components: CMOS Logic Gates NOR GateNAND GateABOut00 101 110 111 0ABOut00 101 010 011 0OutABABOutOut = A + BOut = A • BVddABOutVddABOut1/28/04 ©UCB Spring 2004CS152 / Kubiatowicz Lec3.34Basic Components: CMOS Logic Gates OutABCDMore Inputs More asymmetric Edges Times!VddOutBCDA4-input NAND Gate1/28/04 ©UCB Spring 2004CS152 / Kubiatowicz Lec3.35Ideal versus Reality °When input 0 -> 1, output 1 -> 0 but NOT instantly•Output goes 1 -> 0: output voltage goes from Vdd (5v) to 0v°When input 1 -> 0, output 0 -> 1 but NOT instantly•Output goes 0 -> 1:


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Berkeley COMPSCI 152 - Lecture 4 – Timing

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