For always-on IoT silicon, leakage matters more than dynamic power. Your floorplan locks in the voltage-domain topology — change it later and you redo everything.
Voltage Islands
Group always-on logic together. Isolate switchable domains with header/footer cells and level shifters at boundaries.
Retention Strategy
Save state across power-down with retention flops. Cost: 2-4× area per flop. Use sparingly.
UPF Discipline
Write the UPF before the floorplan. Then the floorplan implements UPF — not the other way around.