What are supply-set relationships, and what does the -resolve option of create_supply_net control?

Short Answer

Supply sets are related when they resolve to the same nets, which you declare with associate_supply_set (UPF). -resolve on create_supply_net (UPF) decides the state and voltage of a net that has more than one supply source. The default, unresolved, allows one source only, so a net fed by two switches needs one_hot, parallel, parallel_one_hot or a named resolution function.

Technical Explanation

• Association: associate_supply_set (UPF) makes two supply sets resolve to the same power and ground nets, so tools treat them as connected.
• unresolved is the default: one source only, and a second source is an error.
• one_hot: sources with different root drivers, at most one on at a time. Two on together make the net UNDETERMINED.
• parallel: switches in parallel from one root supply. The net is FULL_ON when all are on and PARTIAL_ON when only some are.
• parallel_one_hot applies one_hot across root drivers and parallel within each; a custom function name covers anything else.
• ICC2 wants -resolve parallel (UPF) when one net ties the internal PG pins of several macros with fine-grained switches.
• ICC2 stores a custom function name and checks for conflicts but does not evaluate it; simulation does.

# [UPF]  design.upf
create_supply_net VDD_DVS -domain PD_GPU -resolve one_hot
create_power_switch SW_HI -domain PD_GPU -input_supply_port {in VDD0p9} -output_supply_port {out VDD_DVS} -control_port {ctrl sel_hi} -on_state {ON in {ctrl}}
create_power_switch SW_LO -domain PD_GPU -input_supply_port {in VDD0p75} -output_supply_port {out VDD_DVS} -control_port {ctrl sel_lo} -on_state {ON in {ctrl}}
associate_supply_set SS_GPU_IP -handle PD_GPU.primary
# [ICC2]  icc2_shell
report_supply_sets
check_mv_design

What To Check

• Every supply net with more than one source has a -resolve (UPF) type that matches how its sources behave.
• On a one_hot net, no legal power state turns two sources on at once.
• A net reused in another domain keeps the resolve type of its creating command.
• Associated supply sets really share both power and ground.

Healthy, Suspicious & Hard-stop Results

• Healthy (illustrative): report_supply_sets (ICC2) shows SS_GPU_IP and PD_GPU.primary on the same nets, and check_mv_design (ICC2) reports no supply driver errors.
• Suspicious (illustrative): The power states include one where both SW_HI and SW_LO are on: it loads, but simulation will show VDD_DVS as UNDETERMINED.
• Hard stop: Two switch outputs drive a net left unresolved: that breaks the one-source rule and must be fixed before implementation.

What The Interviewer Is Testing

• Whether you know the default is unresolved, one source only.
• Whether you can match one_hot, parallel and parallel_one_hot to a real switch topology.

Follow-up Question & Model Response

"What does -reuse do to a resolved net?"

Candidate Model Response: -reuse makes a net created for one domain available in another domain of the same scope. The standard says the -resolve value on the reusing command must not conflict with the creating command. So a one_hot net stays one_hot everywhere it is reused. If you need different behaviour, create a separate net.