Walk through how trip points, slew, and the RC-011 extrapolation limit chain together into a single accuracy failure mode.
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Ten-second Interview Answer
Wrong trip points corrupt the measured slew, that slew indexes the driver or CCS tables out of range, delay calc extrapolates (RC-011) and emits a larger output slew, which pushes the next stage further out of range - the error compounds down the path.
Complete Technical Explanation
It is a chain, and each link amplifies the previous one. Trip points define how slew is measured, so if a slew is taken across an unexpected threshold pair the slew value handed to delay calculation is already wrong. That slew is then the index into the driver or CCS tables. If it lands beyond the maximum characterized slew index, delay calculation has no data and must extrapolate, which is what RC-011 reports: a less accurate delay, and - crucially - a larger output slew. That larger slew becomes the input slew for the next stage, indexing its tables even further out of range, producing another RC-011 and another inflated slew. So a subtle trip-point issue cascades into a chain of extrapolations, each stage worse than the last. Breaking the chain has three steps. First, confirm the trip points, meaning the -thresholds settings, are correct so slews are measured across the intended pair. Second, set max_transition from the lowest maximum slew index in the libraries so propagated slews stay inside the characterized range. Third, treat RC-011 as a real signal and fix the library index range rather than widening the clip to silence it. The reason this failure mode is dangerous is that it is invisible if you inspect only one stage; the damage is done by the propagation of an out-of-range slew, not by any single delay number looking obviously wrong.
In Pd / Signoff
In post-route signoff you see this as a cluster of RC-011 messages down one path. The move is to check - thresholds against the library's characterization thresholds, compare max_transition against the lowest maximum slew index across the linked libraries, and use report_delay_calculation on the first offending stage rather than the worst-slack stage - the first out-of-range index is where the chain starts and where the fix belongs.
Common Trap
Chasing RC-011 at the stage with the worst slack, or widening the slew clip to make the messages go away. That hides the compounding rather than stopping it - the real defect is usually a trip-point mismatch or a max_transition set above the library's lowest maximum slew index, several stages upstream.
Expect Next
Given a path with RC-011 at three consecutive stages, how would you determine which stage first went out of range?
Topic And Primetime Commands
Delay Calculation / CCS Modelling. report_delay_calculation
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