What is a supply set in UPF?

Short Answer

A supply set is a named bundle of supply functions, power and ground, plus optional bias functions, that together form one complete power source. Instead of naming each net, you hand a domain or strategy the bundle. You can refer to its functions, such as SS_COP.power, and bind them to real nets now or later.

Technical Explanation

• Supply set: IEEE 1801 defines six functions per set: power, ground, pwell, nwell, deeppwell and deepnwell.
• Each function is a symbolic name for a supply net and can be used anywhere a net is allowed.
• You build one with create_supply_set -function (UPF), binding functions to nets now or leaving them to be bound later.
• Domains have predefined supply set handles, such as PD_COP.primary; associate_supply_set (UPF) ties a handle to a real set.
• Strategies reference sets too, so an isolation strategy names its always-on supply as one object, not two nets.
• Bind a set's power function to the wrong net and every cell or strategy using that set is powered wrongly at once.

# [UPF]  design.upf
create_supply_set SS_COP -function {power VDD1p0_SW} -function {ground VSS}
create_supply_set SS_AON -function {power VDD1p0} -function {ground VSS}
create_power_domain PD_COP -elements {U_COP} -supply {primary SS_COP}

Follow-up Question & Model Response

"Why did UPF add supply sets if nets already worked?"

Candidate Model Response: Nets tie the intent to one specific wire too early. With sets, a block UPF can say what supplies it needs, such as primary and an always-on backup, without knowing the top-level net names. The integrator binds them later, which makes block UPF reusable. Sets also carry power states, so add_power_state (UPF) can describe a set as on, off or at a voltage in one place.