A path in a switchable domain reports the wrong voltage after a power switch. How do you debug it?

Short Answer

Trace voltage in the same order PrimeTime resolves it: report_power_switch (PT) for the switch's On State condition, report_power_network (PT) for the topology it feeds, report_supply_net (PT) for the output net's voltage, then report_timing -voltage (PT) or the pg_pin_info attribute on the cells. The most common root cause is a missing set_voltage on the switch's output net.

Technical Explanation

• Start at the switch itself. Run report_power_switch (PT) and read its On State expression - the logic condition under which the switch actually passes power through. Confirm the control conditions you believe are active really do put the switch in that passing state. If they don't, everything downstream is already explained.
• Then check the topology. report_power_network (PT) shows the actual net connectivity through the switch, telling you whether a path exists at all from the input supply port to the cells you care about, and whether it routes where you think it does.
• Then check the output net's voltage states. report_supply_net (PT) on the switch's output net shows its declared voltage states and ranges - this is where a gap most often hides.
• Finally check what actually reached the cells. report_timing -voltage (PT), or reading the voltage_source field through the pg_pin_info attribute on a cell, shows what voltage genuinely propagated to its power-ground pins. This last step is what distinguishes a wrong voltage from a fallback voltage.
• The single most common root cause. The switch's output net never had a set_voltage (SDC) value applied to it. The switch logic is fine, the topology is fine, but the terminating net carries no voltage assignment, so the tool cannot resolve one and raises a UPF-029-style message.
• What to fix. Add the voltage on the output net rather than hunting for a connectivity bug that likely isn't there.

Follow-up Question & Model Response

Suppose report_power_switch confirms the switch is correctly On, and report_power_network confirms the topology is right, but the path still reports the wrong voltage. What do you check next, and why is it usually the answer?

Candidate Model Response: Once the switch state and topology are both confirmed correct, the next and usually final check is report_supply_net on the switch's output net, looking specifically for whether set_voltage was ever applied to it. This is usually the answer because the switch and the network topology only describe whether power can reach a cell - they say nothing about what voltage value the tool should assign once it gets there. A structurally correct path with no voltage assignment on its terminating net is the single most common way this symptom appears, since it produces exactly the "right connectivity, wrong or missing voltage" signature described in the question.