What isolation placement locations are available (self, parent, fanout, automatic), and how do you choose between them?
From PDVerse Low-Power Physical Design Mentor Guide · pdVerse Mentor Guide
Explanation
The -location option decides where an isolation cell physically/ logically sits relative to the domain boundary: inside the domain being isolated (self), in the surrounding parent domain (parent), replicated at every sink fanout point (fanout), or left for the tool to decide (automatic).
Implementation Walkthrough
The basic self/parent/fanout/automatic placement options follow these usage rules: -location fanout can only be used together with one of -source, -sink, or -diff_supply_only, and isolation_power_net cannot be combined with -location fanout (though it's fine with parent or self).
Command
set_isolation S1 -domain PD_Blue -isolation_supply SS_Orange -applies_to
inputs -sink SS_BlueSwitch-by-switch
self: places the cell inside the domain being isolated; parent:
places the cell in the surrounding parent domain, outside the
boundary; fanout: replicates the cell at every sink fanout location,
and requires one of -source/-sink/-diff_supply_only to be specified;
automatic: lets the tool choose based on design context.Expected Tool Behavior
The chosen location determines which hierarchy level physically hosts the isolation cell instance, and therefore which supply is naturally local and available to it.
Example
A general placement decision mirrors the level-shifter self-vsparent tradeoff for PD_SHUTDOWN -- whether the isolation logic lives with the shutdown block or just outside it in the always-on region.
Common Mistake
Specifying -location fanout without also specifying -source, -sink, or -diff_supply_only, which the tool disallows.
Likely Error Or Warning
This topic is not covered in enough depth here to give a fully reliable answer beyond the stated usage restriction on -location fanout.
Debugging Approach
Use the GUI Power Domain view or report_mv_cells to visually confirm where the isolation cells actually landed; the diagram below documents the full placement matrix of -applies_to x -location (7 variants).
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