Silicon Real Estate: Your Resource Budget

Wed, 31 Dec 2025 09:13:00 +0000

Timing Series: Part 4 of 6

Previous: Pipelining Without Breaking Your Protocol

Friday Afternoon

Friday afternoon. Timing met with 200 ps margin. I merged a teammate’s “small” feature branch-an extra output mux, some debug registers, maybe 2000 LUTs.

Monday morning: 847 failing paths. Six-hour build times. Demo on Thursday.

I hadn’t added logic. I’d crossed the congestion cliff.

Before merge: After merge:
LUT utilization: 89% LUT utilization: 93%
WNS: +0.200 ns WNS: -0.847 ns
Build time: 1.5 hours Build time: 6.2 hours
Failing paths: 0 Failing paths: 847

The utilization report said I was fine. 93% fits. But the router disagreed. Every wire fought for routing tracks. Critical paths detoured through congested regions. Placement became a puzzle with no good solutions.

Utilization on bitwiz

Silicon Real Estate: Your Resource Budget

Friday Afternoon