Outstanding Features of DesignDesign MethodologySlide 3Architecture - SUEArchitecture – Output WaveformsProposed Critical PathCritical Path Sizing MethodologyOutput Waveforms of Critical PathTrade-Offs of our DesignEE 141 Project 2 May 8, 2003 1Outstanding Features of DesignMaximize speed of one 8-bit Division by:i. Observing loop-holes in 8-bit divisionii. Taking advantage of given specsiii. Realizing that we are just maximizing raw SPEEDiv. Optimizing the Critical Path of DesignSummary of Main Results:Critical Path Delay Divide Calculation Latency Clock PeriodOverall Delay6.8 ns 2(6.8) + 2(.05) = 13.7 ns ~7 ns ~15 nsNAMES …EE 141 Project 2 May 8, 2003 2Design Methodology105/26……1111001101101001 00011010 11111001111101001 00011010 1111110100101001 00011010 1111111011001001 00011010 1111111110011001 00011010EE 141 Project 2 May 8, 2003 3Design MethodologyConstraints to take advantage of:4 total adders available – each iteration requires one addOptimize for JUST speed - not throughput, power or sizeShifts are very organized – can just perform needed shifts into circuitUsing fancy logic, wiring and all adders can reduce the number of clock cycles per divideEE 141 Project 2 May 8, 2003 4 Architecture - SUEEE 141 Project 2 May 8, 2003 5Architecture – Output WaveformsEE 141 Project 2 May 8, 2003 6Proposed Critical PathImportant circuits along Critical Path:The critical path is defined entirely by the cascaded 8-bit adder cells. It should be noted that the path is cascading, not Delay = 6.8 ns for adder blockEE 141 Project 2 May 8, 2003 7Critical Path Sizing MethodologySTEPS FOR OPTIMIZATIONThe simplest step is to properly buffer the adder outputs, divisor inputs, and XOR outputs to match the B adder inputs, XOR inputs, and A adder inputs respectively. We used buffer chains of 3-4 inverters and incremental sizing to keep the input/output waveforms consistent between stages.A simple way to make our mirror adder faster was to implement even and odd adder cells, inverting the carry bit back and forth between adjacent cells to remove the inverters necessary to produce correct output carry signals. This also allowed us to remove an inverter from the sum output of the odd adder bit cells taking advantage of the full-adder’s inverting propertyA final small optimization was made by reversing the A and B inputs on the kill/generate stage of the mirror adder to bring the B inputs closer to the output node. Our design essentially wires the divisor (A) inputs directly to the adders, so divisor data is available before dividend/remainder data in at least 3 of the 4 8-bit adders.EE 141 Project 2 May 8, 2003 8Output Waveforms of Critical PathEE 141 Project 2 May 8, 2003 9Trade-Offs of our DesignAdvantages:Simplicity of design – trivial control logicSkip delay of intervening register blocks – only 2 clock cyclesDisadvantages:Bad throughputLong clock cycleAlternative Designs:We could speed up the design using pipelining while keeping the same simple control logic and shifting through
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