An STA engineer receives a setup summary for two DCPeripheral paths: T-A, from a request queue register to config_q, and T-B, which has negative slack. Ask the assistant to extract the report fields and reproduce the arithmetic before discussing improvements. Static timing checks compare modeled timing quantities under constraints. A negative setup slack indicates a failing check in that analysis context; it does not by itself identify the correct RTL change or establish the behavior of every path.
SYNTHETIC normalized setup report T-A; not an EDA tool transcript:
design: DCPeripheral, revision A; units: ns
mode: functional; corner: synthetic_slow; check: setup (max)
startpoint: request_q[0]/Q; endpoint: config_q[0]/D
launch edge = 0.00; launch clock latency = 0.10
clock-to-Q = 0.08; combinational cells = 0.92; nets = 0.60
capture edge = 2.00; capture clock latency = 0.05
setup time = 0.10; setup uncertainty = 0.10
other adjustments, including CPPR = 0.00 in this teaching example
reported arrival = 1.70; reported required = 1.85; slack = +0.15
Second synthetic path T-B, same required time and analysis context:
arrival = 1.97; required = 1.85; slack = -0.12T-A arrival = 0.00 + 0.10 + 0.08 + 0.92 + 0.60 = 1.70 ns
T-A required = 2.00 + 0.05 - 0.10 - 0.10 = 1.85 ns
T-A setup slack = required - arrival = 1.85 - 1.70 = +0.15 ns
T-B setup slack = 1.85 - 1.97 = -0.12 ns
With T-B arrival unchanged, increasing required time by 0.12 ns
would reach zero setup slack for that one check, mathematically.The summary is therefore compatible with T-A passing and T-B failing. Do not summarize the whole design from the first path. The calculation keeps launch and capture latency on their respective sides and subtracts setup time and uncertainty from the capture deadline. Actual reports can include derates, common-path pessimism removal, generated clocks, exceptions, and other adjustments. Preserve the original detailed report instead of forcing those terms into this simplified equation.
PROMPT:
Read T-A and T-B without modifying constraints.
Extract units, check type, mode, corner, endpoints, arrival, and required.
Recompute setup slack. Separate numerical facts from possible causes.
List missing analysis context before proposing engineering action.A useful synthetic response reports the two slacks, asks for the full T-B cell/net breakdown, and requests clock definitions and applicable exceptions. It might propose examining whether net delay dominates, but T-B has no supplied breakdown, so that is a question. The response should also ask which analysis stages supplied parasitics and whether the timing constraints match the intended operating mode. These details decide whether a comparison between reports is meaningful.
Keep the required time at 1.85 ns and reduce T-B arrival by 0.08 ns in a hypothetical candidate. Calculate the new arrival and slack, then state whether the setup check passes. Explain why changing the clock period until this one number is positive is not evidence that DCPeripheral meets its intended target frequency.
Arrival becomes 1.89 ns and setup slack is 1.85 - 1.89 = -0.04 ns, still failing. Another 0.04 ns improvement only reaches zero for this check. Changing the period changes the requirement; it does not demonstrate compliance with the original target or verify other corners, paths, hold checks, or constraints.
This lesson covers one setup calculation, not hold analysis or timing closure. No constraint changes or optimization runs are implied. Read OpenSTA's official overview for its inputs and timing-analysis scope; this is rolling documentation accessed 2026-10-18, so record the actual tool revision in a real review. The provided report format and numbers are synthetic and are not claimed as output from a particular OpenSTA version.