TIMING CLOSURE IN SYSTEM-ON-CHIP ERA Sam Appleton, CEO CONFIDENTIAL

Challenges in SDC Creation & Verification It can get a bit messy “IP”/block level timing Making sure design is fully constrained Finding balance between timing exceptions and risk Verification of timing environment “SoC/Chip level” timing integrating IP Ensuring Hierarchical Consistency Debugging Macro-Scale problems Size & Complexity

IP level timing closure It’s a balancing act! “Minimal SDC” constrain all functional paths for correctness over all modes don’t use any exceptions minimal case analysis minimal clock definitions conservative clock groups “Relaxed SDC” static path/mode exceptions added one SDC per design mode structural/formal MCPs and False Paths Clock/Data exceptions Use clocks to break up timing domains

The Balancing Act Low-Risk Hardest Timing, More Power & Area Higher Risk Easiest Timing, Less Power & Area 1.Find set of timing relaxations that help meet timing goals 2.Ignore all other “available” relaxations that don’t help 3.Allow for reuse of results from previous uses of IP

The Verification Problem “Timing domain” Verification – Debugging clocks, case, modes, conflicts – Ensure STA treatment is correct – Automating manual debug previously done with STA Functional Verification – For exceptions, functional coverage is needed – Simulation OR formal (or both) – Critical problem in signoff of timing environment

SoC Integration Size/Scale – M instances – clocks – IP blocks – k timing exceptions – 2 or 3 levels of hierarchy – 10000s of lines of scripting – Usually GL netlist New Level of Complexity and Scale

SoC Integration Challenges Leverage IP timing SDCs Make sure SoC is consistent with IPs Add toplevel constraints, make sure consistent with IPs

SoC/IP Consistency Critical for Hierarchical Flows Heavy use of ETMs for TAT at toplevel make this more critical Multiple causes of silicon failure Clocks Case Analysis Exceptions Boundary Budget

Future Directions Closing the gap between timing and functional verification – Big need to make sure the timing specification is functionally verified – SDCs are just like any other manually-created input – Finding optimal exceptions to aid in timing closure SoC integration and analysis – Bigger, more complex SoCs – Big need for hierarchical analysis and consistency tools, that can aid with promotion & demotion of SDCs