Quick Reference - 8 Ways to Optimize Power Using Encounter Digital Implementation (EDI) System

Everyone knows that the increasing speed and complexity of today's designs implies a significant increase in power consumption, which demands better optimization of your design for power. I am sure lot of us must be scratching our heads over how to achieve this, knowing that manual power optimization would be hopelessly slow and all too likely to contain errors.

Here are 8Top Things you need to know to optimize your design for power using the Encounter Digital Implementation (EDI) System.

Given the importance of power usage of ICs at lower and lower technology nodes, it is necessary to optimize power at various stages in the flow. This blog post will focus on methods that can be used to reach an optimal solution using the EDI System in an automated and clearly defined fashion. It will give clear and concise details on what features are available within optimization, and how to use them to best reach the power goals of the design.  

Please read through all of the information below before making a decision on the right approach or strategy to take. It is highly dependent on the priority of low power and what timing, runtime, area and signoff criteria were decided upon in your design. With the aid of some or all of the techniques described in this blog it is possible to, depending on the design, vastly reduce both the leakage and dynamic power consumed by the design.

All of the following items discussed here in brief are covered in greater detail in Low Power Optimization in EDI System appnote posted on http://support.cadence.com/

This is a one stop quick reference and not a substitute for reading the full document.

1) VT partition uses various heuristics to gather the cells into a particular partition. Depending on how the cells get placed in a particular bucket, the design leakage can vary a lot. The first thing is to ensure that the leakage power view is correctly specified using the "set_power_analysis_mode -view" command. The "reportVtInstCount -leakage" command is a useful check to see how the cells and libraries are partitioned. Always ensure correct partitioning of cells.

2) In several designs, manually controlling certain leakage libraries in the flow might give much better results than the automated partitioning of cells. If the VT partitioning is not satisfactory, or the optimization flow is found to use more LVT cells than targeted, selectively turn off cells of certain libraries particularly in initial part of the flow i.e. preRoute flow. The user should selectively set the LVT libraries to "don't use" and run preCts/postCts optimization. Depending on final timing QOR, another incremental optimization with LVT cells enabled may be needed.

3) Depending on the importance of leakage/dynamic power in the flow, the leakage/dynamic power flow effort can be set to high or low.

setOptMode -leakagePowerEffort {low|high}
setOptMode -dynamicPowerEffort {low|high}

If timing is the first concern, but having somewhat better leakage/dynamic power is desired, then select low. If leakage/dynamic power is of utmost importance, use high.

4) PostRoute Optimization typically works with all LVT cells enabled. In case of large discrepancy between preRoute and postRoute timings or if SI timing is much worse than base timing, postRoute optimization may overuse LVT cells. So it may be worthwhile experimenting with a two pass optimization, once with LVT cells disabled, and then with LVT cells enabled. 

5) In order to do quick PostRoute timing optimization to clean up final violations without doing physical updates, use the following:

setOptMode -allowOnlyCellSwapping true
optDesign -postRoute 

This will only do cell swapping to improve timing, without doing physical updates. This is specifically for timing optimization and will worsen leakage.

6) Leakage flows typically have a larger area footprint than non-leakage flows. This is because EDI trades area with power, as it uses more HVT cells to fix timing to reduce leakage. This sometimes necessitates reclaiming any extra area during postRoute Opt to get better convergence in timing. EDI has an option to turn on area reclaim postRoute which is hold aware also and will not degrade hold timing.

setOptMode -postRouteAreaReclaim holdAndSetupAware

7) Running standalone Leakage Optimization to do extra leakage reclamation:

optLeakagePower

This may be needed if some of the settings have changed or if leakage flows are not being used.

8) PreRoute Optimization works with an extra DRC Margin of 0.2 in the flow. On some designs it is known to result in extra optimization causing more runtime and worse leakage. The option below is used to reset this extra margin in DRV fixing:

setOptMode -drcMargin -0.2

Remember to reset this margin for postRoute optimization to 0, as postRoute doesn't work with this extra margin of 0.2.  Note that the extra drcMargin is sometimes useful in reducing the SI effects, so by removing the extra margin, more effort may be needed to fix SI later in the flow.

I hope these tips help you achieve your power goals of your designs!

-Mukesh Jaiswal