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Evolution-based Standard Cell Placement

Evolution-based Standard Cell Placement. Jason Woods. Objectives. Implement a heuristic method of simulating an evolutionary process for cell placement Natural selection Iterative Improvements Minimize cell interconnect wire length “Goodness”

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Evolution-based Standard Cell Placement

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  1. Evolution-based Standard Cell Placement Jason Woods

  2. Objectives • Implement a heuristic method of simulating an evolutionary process for cell placement • Natural selection • Iterative Improvements • Minimize cell interconnect wire length • “Goodness” • Achieve results comparable or better than Simulated Annealing • Simultaneous removal of large numbers of cells

  3. Methods • Algorithm divided into two main blocks • Initial setup • Main iterative process

  4. Method: Initial Setup • I/O • Input files • Parameters • Chip Floorplanning • Aspect ratio • Average and maximum row lengths • Initial Placement • Precomputations • Approximation of optimal wire length • “Goodness” of the initial placement

  5. Method: Main Iterative Process • Controlled by user parameters (cpu-time, total wire-length, etc.) • Mutation • Introduces randomness • Evaluation • Determines “goodness” current solution • Judgment • “goodness” ratio determines if cell retains position in the next generation • Cells not retaining position are removed and placed in a priority queue

  6. Method: Main Iterative Process Continued • Sorting of Queue • Comparison done by wire lengths • Allocation • Cells in queue are optimally placed in solution

  7. High-Light of Code: Flow Chart

  8. Data Structures Cell Ports Net Connections Rows Slots Layout Cells Nets Rows Code Structure construteInitialSolution() initialPlacement() doPrecomputations() doESP() mutate() evaluate() judge() allocate() PrintResults() High-Light of Code

  9. Result Representation • Numerical • Final wire length • Optimal wire length • “Goodness” of final solution • Visual • Accurate representation of layout • Aspect ratio • Cell widths • Empty slots

  10. Discussion • Challenges • Computation of optimal wire lengths • Efficient placement of allocated cells in queue • Features • Enforcement of an aspect ratio • Net connections to cells not limited to cell parameter • Implementation of 2 part optimal wire length computation • No need to sort queue • Uses of binary search technique for cell enqueuing

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