CTS Lab 4 Multi-corner balancing

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 Typically the late half of the first defined setup 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

Timing corners

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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 Typically the late half of the first defined setup 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

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 notrequired 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 *

Configuration script example 1/3(No need to run this in the lab)

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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 notrequired 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 *

# Set the primary half corner skew target and set target forhold 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

}

Configuration script example 2/3

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# Set the primary half corner skew target and set target forhold 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

}

# --- Advanced options ---

# Compute fastest buffer size and slew for use over all corners

set_option cts_compute_fastest_drivers_and_slews_for_clusteringmulti_corner

# Do not permit large wire delay variations skews on individualnets

set_optioncts_clustering_net_skew_limit_as_proportion_of_skew_target 0.5

# Spread cells out instead of lumping them together

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

Configuration script example 3/3

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# --- Advanced options ---

# Compute fastest buffer size and slew for use over all corners

set_option cts_compute_fastest_drivers_and_slews_for_clusteringmulti_corner

# Do not permit large wire delay variations skews on individualnets

set_optioncts_clustering_net_skew_limit_as_proportion_of_skew_target 0.5

# Spread cells out instead of lumping them together

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

These settingstypically required onharder 28nmdesigns.

Start CCOpt session and load visualization files:hostname$ cd CTSLAB4hostname$ ccoptccopt% load_visualization SAMPLE/sc_skew.viz.gzccopt% load_visualization SAMPLE/mc_skew.viz.gz

Sample report files:SAMPLE/sc_skew.rpt SAMPLE/sc_trees.rptSAMPLE/mc_skew.rpt SAMPLE/mc_trees.rpt

SAMPLE/mc_full.log

Preparation

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Start CCOpt session and load visualization files:hostname$ cd CTSLAB4hostname$ ccoptccopt% load_visualization SAMPLE/sc_skew.viz.gzccopt% load_visualization SAMPLE/mc_skew.viz.gz

Sample report files:SAMPLE/sc_skew.rpt SAMPLE/sc_trees.rptSAMPLE/mc_skew.rpt SAMPLE/mc_trees.rpt

SAMPLE/mc_full.log

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-cornerreports 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 topright of the skew visualization

Activities

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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-cornerreports 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 topright of the skew visualization

Insertion delay variation visualization

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Insertion delay variation visualization

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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

Only applicable to plain CTS With CCOpt objective is not to balance but to meet multi-corner

multi-mode timing constraints

More advanced options can improve multi-cornerrobustness 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

Summary

10 2013 Cadence Design Systems, Inc. Cadence confidential. Internal use only.

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

Only applicable to plain CTS With CCOpt objective is not to balance but to meet multi-corner

multi-mode timing constraints

More advanced options can improve multi-cornerrobustness 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

11 2013 Cadence Design Systems, Inc. Cadence confidential. Internal use only.