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SymbiFlow / vtr-verilog-to-routing

SymbiFlow WIP changes for Verilog to Routing -- Open Source CAD Flow for FPGA Research
https://verilogtorouting.org
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rr_graph: add delay normalization multiplier to adjust base costs #554

Closed acomodi closed 3 years ago

acomodi commented 3 years ago

With the fix to the rr_graph_indexed_data calculation algorithm that now performs the average on the nodes switches correctly, the base costs for SymbiFlow RR data are now an order of magnitude lower than they used to be, resulting in an increase of run-time during routing.

The adjustment of the pres_fac parameter, despite providing some improvements in run-time, proved to be insufficient to have comparable run-times with the previous higher base costs.

WIth this PR, a new parameter can be used to adjust the delay_normalization factor with a multiplier factor that can get the base_costs back to a comparable size w.r.t. the delay_costs.

litghost commented 3 years ago

This feels like a hack? We should determine why the normalization factor is being computed poorly and propose a fix?