What's the practical difference between symmetric and user-controlled tap driver configuration in an H-tree?

Short Answer

cts.multisource.tap_selection defaults to user, meaning tap positions follow what you specify. Setting it to symmetric produces a symmetric tap configuration automatically instead -- useful when you want the tool to enforce structural symmetry across the H-tree rather than trust manually-specified tap boxes to be symmetric themselves.

Technical Explanation

• cts.multisource.tap_selection defaults to user -- tap positions follow whatever you explicitly specify via -tap_boxes or -tap_locations.
• Setting it to symmetric instead produces a symmetric tap configuration automatically, enforced by the tool rather than relying on your manually-specified positions to already be symmetric.
• This matters because H-tree symmetry is exactly what gives it its skew-robustness advantage -- an asymmetric tap layout undermines the reason you chose an H-tree topology in the first place.
• The symmetric tap-selection mode is set with set_app_options -name cts.multisource.tap_selection -value symmetric -- naming the option (cts.multisource.tap_selection) alone never actually configures it without this wrapping.

Follow-up Question & Model Response

"If H-tree symmetry is what gives it skew robustness, why would tap_selection default to user instead of symmetric?"

Candidate Model Response: Because forcing symmetry isn't always what's wanted -- a floorplan with genuine physical asymmetry (an off-center macro, an irregular voltage area) may need user-controlled tap positions that don't fit a symmetric pattern, so the tool defaults to respecting explicit user intent rather than imposing symmetry unconditionally.