Debug the problems signoff throws at you

Data arrives at 2.033 ns but only 1.890 ns is available (2.000 period, minus 0.050 uncertainty and 0.060 setup), and the path is 18 logic levels deep. A large negative setup slack with normal skew and uncertainty is a long-path problem, the logic cone cannot settle inside one clock period.

Setup is fixed by making data arrive earlier: reduce logic depth (retiming / restructuring), upsize the critical drivers, or borrow time with useful skew. Adding buffers adds delay and makes setup worse; loosening uncertainty just hides the violation instead of closing it.

Hold is a min-delay (short-path) check: the new data must not reach the capture flop too early, before the previous value is safely latched. Here arrival (0.212) is earlier than required (0.270), so data races through, classic post-route hold, independent of clock period.

Hold is fixed by adding delay to the data path, delay cells / buffers on the failing short paths, usually as an automated hold ECO. Watch that the added delay does not eat setup margin on the same path. Everything that fixes setup (going faster) makes hold worse, and vice-versa.

Congestion is a placement problem that surfaces at routing. A local density of 0.92 means the region is nearly full of cells, so their pins and local nets demand more routing tracks than M3/M4 can provide. The fix belongs upstream, in placement, not in the router.

Lower the local demand: add cell padding or a partial placement blockage over the hotspot, cap density with a screen, and re-place so the cells fan out. That trades a little area for a routable design. Timing and clocking knobs do nothing for a routing-supply problem.

Skew is the difference in clock arrival between endpoints, here 312 ps to u_mem versus 225 ps to u_alu, an 87 ps spread. It comes from unequal insertion delay across the tree, and it eats directly into both setup and hold margins.

Balance the insertion delays so every sink sees the clock at nearly the same time (buffer sizing, level balancing, NDR on long branches). Skew is not purely an enemy: once balanced, you can push a little useful skew onto specific launch/capture pairs to buy setup or hold margin deliberately.

Transition time is the driver's strength against the capacitance it has to charge. An X1 buffer driving 32 pins and 78 fF charges the net slowly, so the edge takes 1.24 ns. Slow edges also add delay to every cell they drive and waste short-circuit power, which is why max transition is a design rule and not a suggestion.

Give the net more drive (BUF_X4 or larger), or split the 32 loads across two or three buffers so each driver sees a fraction of the load. A long net also gets a repeater in the middle. Relaxing the limit only hides the problem: the library tables stop at that slew, so any timing beyond it is extrapolated and cannot be trusted.