CTS Lab 4 (Multicorner).pdf

CTS La Lab 4 – Multi-corner balan anc cing

Timing corners • Each timing corner has two “half-corners”: – Early : setup capture, hold launch – Late : setup launch, hold capture – Corresponds to –late –early in some SDC commands

• CTS primary half-corner – – Used for clustering and initial balancing analysis

• All half-corners – Considered for “skew fixing” – i.e. detailed buffer size, place adjustment to close on skew targets

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© 2013 Cadence Design Systems, Inc. Cadence confidential. Internal use only.

Configuration script example 1/3 (No need to run this in the lab) log_on db_restore ../CTSLAB1/SAMPLE/crypto_dma_raid_pse_top.pre.azdb # Spread cells out to improve routability set_option cts_cell_density 0.5 # Tighten global slew target. Actually this is probably not required as cts_compute_fastest_drivers_ and_slews_for_clustering has picked 75ps. set_option cts_target_slew 0.080 set_option cts_target_nonleaf_slew 0.080 # Enable multi-corner balancing config_icts -skew global_multicorner -cg_opt off * 3


Configuration script example 2/3 # Set the primary half corner skew target and set target for hold corner. foreach sg [get_skew_groups *] { set_property cts.target.skew.max:setup.early $sg ignore set_property cts.target.skew.max:setup.late $sg 0.090 set_property cts.target.skew.min:hold.early $sg 0.050 set_property cts.target.skew.min:hold.late $sg ignore }

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Configuration script example 3/3 # --- Advanced options --# Compute fastest buffer size and slew for use over all corners set_option cts_compute_fastest_drivers_and_slews_for_clustering multi_corner # Do not permit large wire delay variations skews on individual nets set_option cts_clustering_net_skew_limit_as_proportion_of_skew_target 0.5 prea

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set_option cts_add_wire_delay_in_detailed_balancer true # Always place cells in the centre of their fanout bounding box (helps reduce wire delay variations in individual clusters) set_option cts_put_driver_in_centre_of_fanout_bounding_box true

# Run CTS (no datapath optimization) icts -timing ignore

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These settings typically required on harder 28nm designs.

Preparation • Start CCOpt session and load visualization files: hostname$ cd CTSLAB4 hostname$ ccopt ccopt% load_visualization SAMPLE/sc_skew.viz.gz ccopt% load_visualization SAMPLE/mc_skew.viz.gz • Sample report files: SAMPLE/sc_skew.rpt SAMPLE/mc_skew.rpt

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SAMPLE/sc_trees.rpt SAMPLE/mc_trees.rpt SAMPLE/mc_full.log


Activities • Examine the multi-corner CTS log, examples: – “Clock tree balancer configuration for skew_group:clk_fast/func_mode” ... – “Skew group summary at end of CTS” ...

• Examine and compare the single corner and multi-corner re orts and skew visualizations – SAMPLE/*.rpt, SAMPLE/*.viz.gz – Note the insertion delay histogram in SAMPLE/mc_skew.rpt (generated with report_skew_groups -histograms)

• Change timing corner and “half-corner” using controls at top right of the skew visualization

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“Insertion delay variation” visualization

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“Insertion delay variation” visualization

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Summary • Multi-corner balancing configuration • Insertion delay variation in skew clock tree visualization • Default AZTCL script written by “ccoptDesign –cts” configures for multi-corner balancing – CTS automatically infers skew targets for corners which are not set

• Onl a

licable to lain CTS

– With CCOpt objective is not to balance but to meet multi-corner multi-mode timing constraints

• More advanced options can improve multi-corner robustness – Deal with scaling mismatch between wire and cell delays – Deployable both in full CCOpt and plain CTS – Although options shown in earlier script this is beyond scope of this training – R&D activities 10


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CTS Lab 4 (Multicorner).pdf

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