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Sensitivity‐Based Leakage Optimization
Software User Guide
Version 0.4.3
Release 2011.8
VLSI CAD Laboratory
UC San Diego
http://vlsicad.ucsd.edu
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Contents
1. Introduction .............................................................................................................................. 3
2. Getting Started ......................................................................................................................... 4
Preparations .............................................................................................................................................. 4
Environment file ........................................................................................................................................ 4
Command file ............................................................................................................................................ 6
3. Leakage Power Optimization Flow ......................................................................................... 11
4. Timing Closure Flow ............................................................................................................... 13
5. Appendix A. Setup File (Example) .......................................................................................... 14
6. Appendix B. Environment File (Example) ............................................................................... 15
7. Appendix C. Command File (Example) ................................................................................... 16
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1. Introduction
This document describes how to use the SensOpt software to optimize leakage power and timing
requirements in digital design. SensOpt performs post‐layout stage cell swapping using multi‐Vt and
multi‐Lgate cells based on the sensitivity function. SensOpt is able to size cells with logical equivalents
and provides an ECO flow. SensOpt supports Multi‐Mode Multi‐Corner (MMMC) feature, which allows a
timing analysis with multiple constraints and libraries.
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2. Getting Started
SensOpt exploits Synopsys PrimeTime (or Extreme DA GoldTime) in static timing analysis and uses
Cadence SOC Encounter in ECO flow. To run SensOpt, PrimeTime (v2004.12 or higher) or GoldTime
(v2010.06 or higher) should be available. SOC Encounter (v7.1 or higher) is required for ECO flow of cell
sizing case.
Preparations
Before running SensOpt, the paths and licenses for PrimeTime (or GoldTime) and SOC Encounter should
be prepared. A path for SensOpt binary can be specified by the following command in c‐shell:
An example of setup file is in Appendix A (also in <install_directory>/SensOpt/tutorial/env.csh>).
SensOpt software is executed with the following command:
<environment file> is used to set environment variables and library information. <command file>
contains information of input/output files and command options.
Environment File
In the environment file, following information is specified.
Example of environment file is in Appendix B (also in <install_directory>/SensOpt/tutorial/<test_case>
/test.env).
-home <install_directory/SensOpt> -dbpath <directory path of .db files> -db <.db library files> -libpath <directory path of .lib files> -lib <.lib library files> -lef <.lef files of standard library and macro cells> -capw <capacitance table for SOC Encounter (cworst)> # required only for ECO -capb <capacitance table for SOC Encounter (cbest)> # required only for ECO -suffix [<name suffix for multi-Vt or mulit-Lgate libraries> ] -mmmcEnv <MMMC environment file> # required only for MMMC mode
% SensOpt -env <environment file> -f <command file>
% set path=(<install_directory>/SensOpt/bin $path)
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Home directory (‐home)
Install directory of SensOpt should be specified with “‐home” option.
Library path and files (‐dbpath, ‐db, ‐libpath, ‐lib)
Synopsys DB (.db) and liberty (.lib) files are specified with this option. Multi‐Vt and multi‐Lgate libraries
can be specified by adding libraries repeatedly (please see Appendix B).
LEF files (‐lef)
Library Exchange Format (LEF) files are provided with “‐lef” option. The LEF is used at OpenAccess and
SOCEncounter in SensOpt flow.
Capacitance table (‐capw, ‐capb)
Capacitance tables for worst and best corner cases are provided with “‐capw” and “‐capb” options.
When the cell swap is performed without ECO case, the capacitance table will not be required (This
information is required only for SOC Encounter).
Suffix of library cell name (‐suffix)
Naming convention for multi‐Vt and munti‐Lgate cells is specified with “‐suffix” option. During the
optimization flow, cell swap (Vt assignment and CD biasing) is performed with this naming convention –
SensOpt replaces suffix patterns to find candidate cells for the cell swap. For example, four kinds of 2
input AND gate (AN2D0) cells can be specified with different suffixes ‐ [_LVT], [_NVT_N05], [_NVT_P05]
and [_HVT]. In this case, AN2D0_LVT, AN2D0_NVT_N05 (NVT with ‐5ns CD biasing), AN2D0_NVT_P05
(NVT with +5ns CD biasing) and AND2D0_HVT cells can be swapped with each other during the
optimization. The suffix pattern allows NULL case with “‐suffix []” and can be used as a prefix pattern.
Example) LVT_AN2D0, AN2D0 and HVT_AN2D0 case: –suffix [LVT_], ‐suffix [], ‐suffix [HVT_]
MMMC environment file (‐mmmcENV)
Different libraries and SDC files can be specified in MMMC environment file (please see Appendix B).
MMMC analysis mode is enable by “‐mmmc” option in the command file.
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Command File
In the command file, following information is specified.
Example of environment file is in Appendix C (also in <install_directory>/SensOpt/tutorial/<test_case>
/test.env). In the command file, design name (‐c) is required and four input files (.v, .def, .spef, .sdc)
should be provided. All other options can be optional.
-mode mode for SensOpt (1 ~ 4) # default: 1(leakage optimization) -op option of cell swap or sizing (1 | 2) # default: 1(cell swap) -c <design name> # top-level instance name -v <Verilog input file> # default: {design name}.v -def <DEF input file> # default: {design name}.def -spef <SPEF input file> # default: {design name}.spef -sdc <SDC files> # default: {design name}.sdc -ck <clock port name> # default: clk -n number of swaps before STA (integer) # default: 0 (optional) -sf sensitivity function (1~4) # default: 1 (optional) -opt_effort optimization effort (high | medium | low) # default: medium (optional) -hold check option for hold time violation (0 | 1) # default: 1 (optional) -maxTr check option for max transition violation (0 | 1) # default: 1 (optional) -g guardband during optimization (unit: ns) # default: 0.0 (optional) -rpt <report output file> # default: result.rpt -vout <netlist output file> # default: {design name}_eco.v -defout <DEF output file> # default: {design name}_eco.def -spefout <SPEF output file> # default: {design name}_eco.spef -mmmc enable MMMC mode # default: false -eco enable SOCE ECO procedure # default: false -noPTPX disable PrimeTime-PX feature # default: false (enable PT-PX) -PTSI enable PrimeTime-SI feature # default: false (disable PT-SI) -useGT use GoldTime in static timing analysis # default: false (use PrimeTime) -dont_touch_inst <instance> -dont_touch_cell <cell name>
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Mode for SensOpt (‐mode)
1: leakage optimization
2: timing closure
3: leakage optimization + timing closure
4: fix max‐transition violation
10: leakage optimization (B. Zahn SNUG 2008 method)
Option for SensOpt (‐op)
1: use cell swapping method with multi‐Vt and multi‐Lgate libraries. Multi‐libraries are specified with “‐
lib” and “‐suffix” options in the environment file. (See Appendix B.)
2: use cell sizing method with logical equivalent cells. The logical equivalent cells are recognized from
Liberty (.lib) files – ‘footprint’ information.
Number of swaps (‐n)
If the value is larger than ‘1’, SensOpt performs multiple swaps at a time to expedite runtime. If the
value is ‘0’ (default), SensOpt performs multiple swaps as many as possible. With multiple swaps at a
time, runtime can be improved significantly.
Optimization effort (‐opt_effort)
The “‐opt_effort” option controls optimization effort. Using higher effort value will allow optimization to
run longer, which can lead to better leakage reduction QoR. “high”, “medium” and “low” effort can be
selected (default: medium).
Sensitivity function (‐sf)
During the leakage optimization and timing closure, cell swap is performed according to the cell
sensitivity. Each sensitivity function can be selected as following table
sensitivity option description for sensitivity function (leakage optimization)
1 Δleakage slack
2 Δleakage / ∆delay
3 Δleakage slack / ∆delay
4 Δleakage / ∆slack
sensitivity option description for sensitivity function (timing closure)
1 Δslack / δ slack WNS
2 Δslack / δ slack WNS ∆leakage
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Δleakage: the change (improvement) of leakage power after a cell is swapped
Δdelay: the change of cell delay (maximum delay of each timing arc) after a cell is swapped
slackmin: the minimum slack among all timing arcs in a cell after a cell is swapped
Δslack: the change of minimum cell slack after a cell is swapped
WNS: worst negative slack of current design
δ: small positive value
Check option for hold time and max transition violation (‐hold, ‐maxTr)
If the option is specified as ‘1’, the violation is considered during leakage and timing optimization.
Guardband option (‐g)
The guardband delay (unit: ns) is considered during the optimization. After cell swapping, if slack of the
cell is less than guardband value, the swap is restored.
Output files (‐rpt, ‐vout, ‐defout, ‐spefout)
Report file and design output files are generated with the name in this option.
MMMC mode (‐mmmc)
MMMC analysis is enable with “‐mmmc” option.
ECO operation (‐eco)
With “‐eco” option, ECO operation is performed automatically with SOCE. If this option is not enabled,
SensOpt just provides cell swap list (eco.tcl) with SOCE ECO format.
PT‐PX operation (‐noPTPX)
SensOpt obtains the leakage result from PrimeTime‐PX (default). With “‐noPTPX” option, SensOpt
calculates the leakage power from liberty (.lib) files. If you have no license for a PrimeTime‐PX feature,
this option should be specified. If ‘‐useGT’ is set, this option is automatically set.
PT‐SI operation (‐PTSI)
With “‐PTSI” option, SensOpt enables PrimeTime SI feature, which makes a crosstalk analysis with the
cross‐coupled capacitance information. If you have no license for a PrimeTime‐SI feature, this option
should not be specified. If ‘‐useGT’ is set, this option is automatically reset.
STA option (‐useGT)
SensOpt can change a static timing analyzer with “‐useGT” option. Without this option, SensOpt uses
PrimeTime in static timing analysis (default). If “‐useGT” is specified in the command file, SensOpt uses
GoldTime in STA.
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Don’t touch cell (‐dont_touch_cell)
Specified library cells are not touched during cell swap or sizing operation. Wildcard (*) can be used in
the cell name. This command can be repeated to specify cells.
Don’t touch instance (‐dont_touch_inst)
Specified instances are not touched during cell swap or sizing operation. Wildcard (*) can be used in the
instance name. Entire instances in a sub‐module can be specified also with the wildcard character (ex. ‐
dont_touch_inst mod‐A/*). This command can be repeated to specify instances.
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Design Data ‐ Inputs
Input type Description
LEF The LEF file contains technology, cell boundary and pin data. A LEF description is required for each cell in the library and macro cells.
Synopsys DB and liberty files
Synopsys DB (.db) and liberty (.lib) files contain timing and power characterization data for cell library.
SDC The SDC file contains timing constraint information that drives optimization decisions.
SPEF The SPEF file contains segment level parasitic information that is used for delay calculation during optimization.
Verilog The Verilog netlist contains connectivity information used during timing analysis.
Capacitance table The capacitance table is used for RC extraction in the SOC Encounter.
Design Data ‐ Outputs
Out type Description
Reports SensOpt generates output report files (including reports on timing and power).
ECO script SensOpt generates ECO scripts (eco.tcl for SOCE and swaplist.tcl for PrimeTime and GoldTime) which can be used at SOC Encounter directly.
Verilog The optimized Verilog file generated by SensOpt. (NOTE: This version of SensOpt can write a flattened‐netlist only. In a hierarchical netlist case, output netlist should be generated alternatively from ECO lists ‐ eco.tcl, swaplist.tcl)
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3. Leakage Power Optimization Flow
In leakage optimization mode, SensOpt analyzes the entire design and reduces leakage power while
satisfying design performance constrains – i.e., setup time, hold time and max transition.
Open Access(lef2oa, def2oa)
cell library(. lef)
design (.def)
design (.v, .spef)
PrimeTime(or GoldTime)
SensOptOA db
Tcl socket
I/F
1. read design2. sensitivity calculation3. swap cells and check timing
- multi-Vt cell- multi-Lgate cell- logical equivalent cell (resize)
4. write netlist result or swap list
design out (.v)
SOC Encounter(optional )
ECOresults
Figure 1. SensOpt optimization flow
Figure 1 describes the optimization flow of SensOpt. SensOpt reads design from OpenAccess and
performs optimization base on sensitivity of each cell. To reduce power, SensOpt downsizes cells with
two methods – 1. cell swap with multi‐Vt or multi‐Lgate libraries, and 2. cell sizing with logical equivalent
cells. During the optimization, timing and power information is updated from PrimeTime (or GoldTime) –
via Tcl sockets (TCP connections). After finishing the optimization, ECO flow is performed if cells are
sized with the logical equivalent cells.
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Algorithm 1 shows the detail heuristic of leakage optimization. In the code, SSTA is a standard static
timing analysis and ISTA(c) is an incremental STA after cell c is changed. Algorithm 2 shows an
implementation for one of sensitivity function.
Cell swap with multi‐Vt or multi‐Lgate libraries (‐op 1)
SensOpt performs post‐layout stage cell swapping using multi‐Vt and multi‐Lgate cells. To swap with
other library cells, all libraries should be provided with “‐db” and “‐lib” option in the environment file.
And, the naming convention should be provided with “‐suffix” option. In downsizing procedure (line 10
in Algorithm 1), cell will be swapped according this suffix naming convention. For example, if _LVT, _NVT
and _HVT suffixes are provided, AN2D0_NVT cell will be downsized with AN2D0_HVT cell. In the cell
swap case, ECO flow is not required.
Cell size with logical equivalent (‐op 2)
SensOpt is able to size cells with logical equivalents and provides an ECO flow. Logical equivalent cells
are recognized from Synopsys Liberty (.lib) file. In the downsizing procedure, cell is re‐sized with a
smaller cell. For example, AN2D4_NVT cell will be downsized with AN2D2_NVT cell since AN2D4_* and
AN2D2_* have same foot print in the liberty (.lib) file. After finishing the optimization, SensOpt
generates ECO list (eco.tcl) and executes ECO procedure automatically with Cadence SOC Encounter.
MMMC analysis (‐mmmc)
SensOpt supports Multi‐Mode Multi‐Corner (MMMC) feature also in timing analysis. If the MMMC mode
is enabled with “‐mmmc” option, additional PrimeTime (or GoldTime) sockets are opened and timing
violation (setup, hold and max transition) is checked in each PrimeTime (or GoldTime) socket. In the
additional sockets, different libraries (for different condition) and different SDC files (for different mode)
can be loaded. Libraries and SDC files for each socket can be specified with “‐mmmcEnv” option in the
environment file.
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4. Timing Closure Flow
SensOpt can repair timing violations with cell swap or cell sizing method. Timing closure flow of SensOpt
is similar to its leakage optimization flow. SensOpt upsizes cells in the critical paths with a negative
timing slack. This timing closure flow can be used after the leakage optimization when the timing
violation is produced during the leakage optimization.
Algorithm 3 presents pseudocode of the timing closure.
In the timing closure flow, SensOpt does not support cell sizing with logical equivalents and only cell
swap is used. It is because that cell sizing to the larger cell makes ECO side effects (the cell should be
placed in other space and this can make timing violation).
SensOpt can also repair max transition violation with cell swap or cell sizing method (‐mode 4).
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5. Appendix A. Setup File (Example)
setenv LM_LICENSE_FILE [email protected] # license setup for PrimeTime and SOCE
setenv PRIMETIME /home/tool/synopsys/PrimeTime/C‐2009.06‐SP2
setenv EXTREME_DA /home/tool/extreme‐da/goldtime‐2010.06.r1
setenv ENCOUNTER /home/tool/cadence/SOC81
setenv SENSOPT /home/tool/SensOpt
setenv OA_PATH /home/tool/SensOpt/oa
setenv LD_LIBRARY_PATH /home/tool/SensOpt/oa/linux_rhel21_32/opt:$LD_LIBRARY_PATH
set path=($PRIMETIME/bin $path)
set path=($PRIMETIME/lib $path)
set path=($EXTREME_DA/bin $path)
set path=($ENCOUNTER/bin $path)
set path=($OA_PATH/bin $path)
set path=($SENSOPT/bin $path)
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6. Appendix B. Environment File (Example)
* Naming suffix should be provided in order of delay – from faster cells to slower (low power) cells.
* ‐capw, ‐capb information is needed only for cell sizing (‐op 2 in the command file) + SOCE ECO flow.
* MMMC environment file (mmmc_bst.env)
* If you are using GoldTime in STA, ‘‐libpath’ and ‘‐lib’ should be specified instead of ‘‐dbpath’ and ‘‐db’.
‐name mmmc_bst
‐dbpath /home/ TOOL/SensOpt/tutorial/libraries/db/bst
‐db LVT_P00.db
‐db NVT_P00.db
‐db HVT_P00.db
‐sdc test.mmmc_bst.sdc
‐home /home/TOOL/SensOpt
‐dbpath /home/ TOOL/SensOpt/tutorial/libraries/db/wst
‐db LVT_P00.db
‐db NVT_P00.db
‐db HVT_P00.db
‐libpath /home/ TOOL/SensOpt/tutorial/libraries/lib/wst
‐lib LVT_P00.lib
‐lib NVT_P00.lib
‐lib HVT_P00.lib
‐lef /home/TOOL/SensOpt/tutorial/libraries/lef/LVT_P00.lef
‐lef /home/TOOL/SensOpt/tutorial/libraries/lef/NVT_P00.lef
‐lef /home/TOOL/SensOpt/tutorial/libraries/lef/HVT_P00.lef
‐lef /home/TOOL/SensOpt/tutorial/libraries/lef/register_files.lef
‐capw /home/TOOL/SensOpt/tutorial/libraries/cap/cworst.captable
‐capb /home/TOOL/SensOpt/tutorial/libraries/cap/cbest.captable
‐suffix [_LVT_P00]
‐suffix [_NVT_P00]
‐suffix [_HVT_P00]
‐mmmcEnv mmmc_bst.env
‐mmmcEnv mmmc_wst_scan.env
‐dont_touch_cell AOI*
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7. Appendix C. Command File (Example)
‐mode 1
‐op 1
‐c lsu_stb_ctl
‐ck rclk
‐def lsu_stb_ctl.def
‐spef lsu_stb_ctl.spef
‐v lsu_stb_ctl.v
‐sdc lsu_stb_ctl.sdc
‐n 0
‐sf 1
‐hold 1
‐maxTr 1
‐g 0.01
‐rpt result.rpt
‐vout lsu_stb_ctl_eco.v
‐defout lsu_stb_ctl_eco.def
‐spefout lsu_stb_ctl_eco.spef
‐mmmc
