How to calculate capacitance for setRC.tcl #3429
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Hello! I need to calculate per-lenght capacitance for "set_layer_rc" in setRC.tcl. It doesn't present at PDK and I am trying to calculate it from the data presented at tech.lef file. Can someone describe me how can I do it? |
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Could you give me a formula, beacuse I am using (CAPACITANCE CPERSQDIST x segment width x segment length) + |
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If the parasitics info is already in the tech LEF file, then you don't need to add a setRC.tcl on top of it unless you are trying to override the values from the tech LEF. That being said, we have found that only very old processes store their parasitics in the tech LEF and the numbers presented don't tend to correlate well with the post-extraction netlist. It is fine for prototyping, but you might want to look into ORFS correlateRC.py to for better parasitics correlation. |
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Then why does Nangate45's setRC.tcl have the "set_layer_rc" parameter, although CAPACITANCE CPERSQDIST, EDGECAPACITANCE and RESISTANCE RPERSQ are explicitly defined in Nangate45's tech LEF? |
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There is some assumed density built into those values. We found they didn't correlate as well to OR's results |
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If the parasitics info is already in the tech LEF file, then you don't need to add a setRC.tcl on top of it unless you are trying to override the values from the tech LEF.
That being said, we have found that only very old processes store their parasitics in the tech LEF and the numbers presented don't tend to correlate well with the post-extraction netlist. It is fine for prototyping, but you might want to look into ORFS correlateRC.py to for better parasitics correlation.