What command applies OCV/AOCV derating, and how do -early/-late and cell_delay/-net_delay/-clock/-data qualifiers change what gets derated?

Short Answer

set_timing_derate (SDC) is the command that applies OCV derate factors. Its qualifiers scope exactly what gets multiplied: -early or -late chooses shortest-path or longest-path delays, -cell_delay/-net_delay/-cell_check chooses which kind of delay component, and -clock/-data chooses which side of the path. Omitting a scoping qualifier applies the factor to everything in that early/late direction across the whole design.

Technical Explanation

• set_timing_derate (SDC) always requires either -early or -late — there is no default direction, because the two directions model opposite physical assumptions (early models a fast corner for the shortest-path side of a check, late models a slow corner for the longest-path side), and applying both needs two separate commands.
• Using the command at all implicitly switches the tool into on-chip variation analysis mode, equivalent to set_operating_conditions -analysis_type on_chip_variation (SDC/PT) — a detail worth knowing, since a stray set_timing_derate left in a script changes the whole analysis mode, not just one number.
• -cell_delay and -net_delay (SDC) scope the factor to just cell delays or just net (interconnect) delays; -cell_check (SDC) scopes it to library setup/hold check margins themselves, as distinct from propagation delay through a cell.
• -clock and -data (SDC) scope the factor to only the clock network or only the data path, letting a designer apply a different derate to clock buffers (often built from higher-drive, more uniform cells) than to the general standard-cell data path.
• Qualifiers combine: set_timing_derate -clock -increment -late 0.10 [get_cells ...] (SDC) adds an incremental late derate scoped to clock cells within a specific cell list, on top of whatever base derate already applies design-wide — -increment adds to rather than replaces the existing factor for that scope.
• With no cell/pin/clock argument at all, set_timing_derate -late 1.2 (SDC) applies late derating to every late (longest-path) cell and net delay in the whole design; adding a qualifier and an object list narrows that scope, and more specific settings take precedence over the broader design-wide default.
• report_timing -derate (PT) prints the per-segment derate factor actually used for a given reported path, and report_timing_derate (PT) reports the derate settings currently configured — both are the way to confirm a layered set of -clock/-data/-cell_delay qualifiers resolved the way intended, rather than assuming the last command written wins.

Follow-up Question & Model Response

"If you need clock buffers to carry a tighter derate than the rest of the design because they come from a more uniform, high-drive cell subset, how would you set that up without breaking the design-wide setup and hold coverage?"

Candidate Model Response: I would first set the design-wide early and late derate factors that apply to all cells and nets, covering both setup and hold globally. Then I would add -clock-scoped set_timing_derate commands, again with both -early and -late, using the tighter factor appropriate to the clock buffer subset — the clock-scoped commands narrow the derate only for clock-network cells and leave the data path at the design-wide value. I would finish by running report_timing_derate to confirm the clock-scoped values actually took effect over the broader default, since a scoping mistake here silently reverts clock cells back to the design-wide factor.