What is the "primary power net" of a power domain?
From PDVerse Low-Power Physical Design Mentor Guide · pdVerse Mentor Guide
Definition
The primary power net (together with the primary ground net) is the main supply that every cell inside a power domain is implicitly connected to, unless a cell has a special explicit connection otherwise — it's designated with set_domain_supply_net, and every power domain must have exactly one primary power net and one primary ground net.
Mentor Explanation
A beginner often assumes cells need to be individually wired to a supply — but the point of designating a primary power net is that it becomes the implicit default: every cell placed in that domain is automatically understood to draw from it without a per-instance connection statement. Think of it this way: it's the domain's 'default rail.'
Example
In the MYCHIP example, the shutdown domain PD_COP designates its own switched net, VDD1p0_SW, as its primary power net — distinct from the always-on VDD1p0 net that feeds the rest of the chip.
Why It Matters
The primary power net is the reference point for almost everything else about the domain — power state definitions, retention strategy defaults, and isolation-supply defaults all key off it.
Command
set_domain_supply_net -primary_power_net -primary_ground_netCommon Beginner Mistake
A beginner mistake is confusing the primary (often switched) power net with the alwayson backup net used for retention/isolation — in the MYCHIP example these are deliberately different nets (VDD1p0_SW vs. VDD1p0) precisely because isolation and retention logic must stay powered when the domain's primary supply is off.
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