Post on 26-Jul-2020
transcript
Find EDA Tools for A Faster Timing Closure with
ECO & Clock Path ECO
Anne Yue
Synapse Design 2200 Laurelwood Rd. Santa Clara, CA 95054
Abstract
• This paper describes and compares the current EDA tools for STA, timing closure and timing ECO. In-depth studies on ETS, PrimeTime & Dorado let us understand the can/cannot of the tools.
• Proven-in-silicon workarounds are efficient for a faster timing closure. 3 solutions are shared in this paper to solve the left-over issues from PrimeTime ECO tool.
• One of the solutions(Upsizing DFF) will be Enhancement features in future PrimeTime release(2013.06).
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Agenda
• Challenges for SOC Timing Closure
• Who Can Help on STA?
• Who Can Help on Timing ECO?
• Solutions with Clock Path ECO
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Challenges for SOC Timing Closure
• ASIC design size increasing exponentially every year.
• 20 million instance designs last year. 65 million instance designs this year.
• With 32nm & less technology, temperature inversion and power related analysis bring in more PVT corners for timing STA.
• One ECO loop can take 3~5 days.
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Who Can Help on STA --- ETS & PrimeTime
• ETS(Encounter Timing System) --- Cadence timing signoff tool
• PrimeTime --- Synopsys timing signoff tool
• ETS & PrimeTime are both silicon-proven timing signoff tools.
• ETS & PrimeTime can work interleave with implementation tools from other companies.
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ETS vs. PrimeTime on Constraints
• The sdc coding style for clock-group related constraints matters to ETS & PrimeTime.
• ETS will interpret differently than PrimeTime on some clock-group definition.
• PrimeTime is more robust than ETS on this.
• With different clock-group understandings, ETS & PrimeTime will give out different sets of report.
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ETS vs. PrimeTime on Design Slack
• If feed with the same quality(good) constraints, slack difference between ETS vs. PrimeTime DMSA --- 70ps with setup, 20ps with hold
• PrimeTime is more pessimistic than ETS.
• In some case ETS cannot report max_tran violation which PrimeTime reported.
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ETS vs. PrimeTime on ECO
• PrimeTime DMSA can generate ECO.tcl for setup/hold/max_trans/max_fanout/max_cap
• DMSA MCMM features very helpful on timing closure with PVT corners/modes
• ETS ECO feature is under-construction. Hold time ECO is in place. No setup ECO.
• ETS is about 2~4 years behind PrimeTime on timing ECO.
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Who Can Help on Timing ECO --- PrimeTime & Dorado
• PrimeTime is with fix_eco_timing & fix_eco_drc
• Same license as PrimeTime & PrimeTime-SI
• Dorado is a 100% ECO tool.
• Dorado does not have build-in timing engine.
Instead, it has ECO-specific engine.
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Dorado in ECO
• Dorado is with ECO for: setup/hold/max_trans/max_cap/max_fanout
• Dorado can generate eco.tcl & eco.def. The incremental .def file will serve as guidance for BackEnd tool ECO legalization, which increase the possibility of ECO process convergence.
• Clock ECO is the highlight for this tool.
• Remove buffers for setup fix.
• A new tool means the tool setup overhead efforts for design team.
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PrimeTime in ECO
• fix_eco_timing can do: -- on Data Path 21
o upsize/downsize cells
o insert buffer
• fix_eco_timing cannot do:
o remove cells.
o change clock path(Clock Path 1 & Clock Path 2)
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PrimeTime DMSA ECO --- Can & Cannot
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DFF 2 DFF 1 Data Path 21
Clock Path 2 Clock Path 1
PrimeTime DMSA ECO --- fixed & left over
• Hold Violations : – 99 ~ 100%
– good job !
• setup Violations : – 85 ~ 90%
– DMSA ECO did very good job on cell-sizing base on MCMM timing analysis.
– But launch/capture clock path are untouched by the tool.
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Before fix_eco_timing:
Setup violations --------------------------------------------------------- Total reg->reg reg->out in->reg in->out --------------------------------------------------------- C2C * -> * WNS -1.45 -1.45 -0.03 0.00 0.00 TNS -390.27 -390.24 -0.03 0.00 0.00 NUM 2788 2787 1 0 0 --------------------------------------------------------- Hold violations --------------------------------------------------------- C2C * -> * WNS -0.78 -0.78 0.00 -0.53 0.00 TNS -12.34 -5.98 0.00 -6.36 0.00 NUM 44 21 0 23 0 ---------------------------------------------------------
After fix_eco_timing:
Setup violations --------------------------------------------------------- Total reg->reg reg->out in->reg in->out --------------------------------------------------------- C2C * -> * WNS -1.45 -1.45 0.00 0.00 0.00 TNS -11.64 -11.64 0.00 0.00 0.00 NUM 376 376 0 0 0 --------------------------------------------------------- No hold violations found
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How to fix the DMSA ECO left over violations ?
• No room for Data Path 21 cell-sizing. MCMM mode DMSA ECO did better job than human in cell-sizing.
• PT_ECO consider DFFs as part of clock network, since the DFF/CK pin is the end point of the clock tree.
• PT_ECO cannot touch the clock path cells. So, DFF2 cell is not upsized by the PT tool.
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Solution I with Clock Path ECO -- Upsizing DFFs
• Upsize the DFFs will benefit the setup fix in the following ways: – DFF component delay # will improve. – New upsized DFF improves the transition delay for
downstream cells, which give possibility for another round of PT_ECO run to optimize the data path cells.
• So we plan to do: upsizing DFF + additional PT_ECO run
• Enhancement to fix_eco_timing to allow DFF sizing will be add into future PrimeTime release(2013.06). Find EDA Tools for A Faster Timing Closure with ECO & Clock Path ECO 16
Solution II with Clock Path ECO -- Clock tree re-stitching
• Clock skew borrowing for left-over setup fix.
• 1st level & 2nd level(~10% chance) borrowing.
• By re-arrange the launch/capture clock to the same CTS branch, we can get the extra CRPR bonus for this in-depth study re-stitching.
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2nd Level Setup Margin Borrowing
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DFF3 DFF2 DFF1
1 2 3 5 4 8 7 6 9 10 11 12
Extra bonus for CRPR with Clock Tree Re-stitching
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DFF 2 DFF 1
Re-stitching
Solution III with Clock Path ECO --- Clock tree in-law unit
• Utilize PD tool(ICC or Encounter) to build the in-law ECO clock structure.
• Targeting insertion # is pre-calculated.
• May need two round of spef->ECO to get the right insertion #.
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Questions
&
Comments
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THANKS
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