How do you connect a supply net to a domain's primary power/ground using set_domain_supply_net?

Short Answer

set_domain_supply_net (UPF) names the primary power and ground nets of a domain, and every cell in that domain is then implicitly tied to them. IEEE 1801-2015 lists it as legacy: the modern form binds a supply set with create_power_domain PD_COP -supply {primary SS_COP} (UPF). Both still load in ICC2 and PrimeTime, so you need to read the old form and write the new one.

Technical Explanation

• Implicit connection: every standard cell in PD_COP gets its power and ground pins tied to the primary nets, with no per-instance connect.
• Modern form: bundle VDD1p0_SW and GND into SS_COP, then give the domain -supply {primary SS_COP}.
• Legacy form (still accepted by ICC2/PT): set_domain_supply_net PD_COP -primary_power_net VDD1p0_SW -primary_ground_net GND (UPF). Both options are required.
• Shutdown domains: the primary must be the switch output VDD1p0_SW. Pointing it at VDD1p0 keeps PD_COP on forever.
• A domain has one primary power and one primary ground. Other supplies reach it as isolation, retention or secondary supplies.
• A new supply net is never primary on its own; ICC2 treats it as primary only after one of these bindings.

# [UPF]  mychip.upf
create_supply_set SS_COP -function {power VDD1p0_SW} -function {ground GND}
create_power_domain PD_COP -elements {U_COP} -supply {primary SS_COP}
# Legacy form (still accepted by ICC2/PT), use instead of the -supply binding
set_domain_supply_net PD_COP -primary_power_net VDD1p0_SW -primary_ground_net GND
# [ICC2]  icc2_shell
report_power_domains
check_mv_design

What To Check

• PD_COP primary power is VDD1p0_SW, the switch output.
• Primary ground is GND in every MYCHIP domain.
• Each domain is bound once, by one method, so there is one source of truth.
• Every primary net has an operating voltage.

Healthy, Suspicious & Hard-stop Results

• Healthy (illustrative): report_power_domains shows PD_COP on VDD1p0_SW and GND, and PD_CPU on VDD0p9 and GND.
• Suspicious (illustrative): PD_COP shows VDD1p0 as primary: the UPF loads, but the domain can never switch off.
• Hard stop: load_upf fails because -primary_ground_net lost its leading dash, or a domain has no primary at all.

What The Interviewer Is Testing

• Do you know this command is legacy and what replaced it?
• Do you tie a shutdown domain to the switch output, not the switch input?

Follow-up Question & Model Response

"If both forms still work, why migrate to supply sets?"

Candidate Model Response: Because the rest of IEEE 1801-2015 is built around sets. Isolation and retention strategies take -isolation_supply and -retention_supply as sets, and power states are written on sets with add_power_state. Mixing a net-based primary with set-based strategies works, but you end up tracking one supply under two names. New UPF should use the -supply binding and keep the legacy command only in inherited files.