Routing pressure
Read the situation and the numbers it starts from, then pick the change you would make. Every option was run, so the answer comes from the measurement rather than from anyone's judgement, and after you choose you see what all of them did. Progress is stored in this browser.
All 2 situations in this kind, with their tables
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Which change clears the congestion at the least cost?Leave it, it routed: 2 · Spread the design out: 2 · Ask for two more layers: 0
Spreading the design does relieve the pressure, cutting the routing resource in use from 58 to 39 percent, and it still does not stop either complaint: global routing runs its extra iterations anyway and the placer still reports that it could not reach the target. It also pays for what it does with 4 percent more wire, because everything is further apart. Two more layers clear both reports while the wire gets shorter, because the router can go up and over instead of around. When the constraint is capacity, giving capacity back is the cheap answer, and moving cells is what you do when you cannot.
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Which way out costs the least?Take the four layers and route it: 2 · Take the four layers and spread the design out: 2 · Go back and ask for the upper layers: 0
Everything here routes. Both restricted runs finished with zero violations and still closed their timing, so whether it fits was never the question. What it costs is. Losing the upper layers adds 20 percent to the wire, 9 percent to the power, and takes the worst voltage drop from 0.83 percent of the supply to 1.38, because more wire is more capacitance and more capacitance is more current. Spreading the design out does relieve the routing, from 66 percent of the resource down to 50, and brings the drop back to 0.85. It pays with more wire than either other option, 29 percent above the ten-layer run, and it still does not stop the flow reporting congestion. So the ranking is the same as on the small block, and the difference at this size is that second best now arrives with a bill.