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PGV Generation in Voltus-Fi-XL

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This section contains information about power-grid views (PGVs), use of PGVs, and how to generate PGVs in Voltus-Fi-XL.

What is Power-Grid View?

A power-grid view (PGV) is a model view of the design that contains information about the power ports of the cell or block. It also contains information about the internal power grid, intrinsic capacitance, and the tap current distribution within the cell or block.

Increasing operating frequency and density of IC designs increases the need for IR drop and Electromigration (EM) power-grid analysis. Power-grid signoff analysis is provided by Voltus in the digital domain, and Voltus-Fi-XL in the analog domain. Voltus-Fi-XL provides the ability to create power-grid views (PGVs) of an analog design block that can be used in Voltus for mixed-signal analysis. PGVs can be generated both in the GUI and batch command mode in Voltus-Fi-XL.

PGVs provide an accurate characterization of capacitance and currents, and power-grid extraction. Voltus uses these views to model power rail and power distribution information for each instance of the cell in the design for dynamic or static full-chip power-grid analysis.

Related Topics

• create_pgv
• Generating Power-Grid Views in Voltus-Fi-XL
• Create Power Grid Views Form

Data Requirements and Flow for PGV Creation

Power-grid view generation in Voltus-Fi-XL depends upon the simulator-generated database and current files. For generating PGVs in Voltus-Fi-XL, ensure the following while performing simulation using Spectre APS/XPS.

• Enable the emir mode. The EMIR analysis is run like a regular APS/XPS simulation with the additional +emir option.
• Generate the current files for all the power nets for which PGVs are being generated. This is done by specifying UTI commands in the Spectre input file. The syntax of the command is as follows:
  

  uti0 uti signal=net_name start=start_time cycles=number_of_cycles_for_this_measure intervals=number_of_points clockcycle=clock_period method=[0|1|2][0|1|2][0|1|2] filename=filename_prefix_for_this_measure termflag=0 Namemangling=0 

  The syntax contains the following parameters:
  • signal=signal_name
    Specifies the net name for which current is to be calculated.
    
    Ensure that the net name is specified along with the instance hierarchy name. For example, if your instance hierarchy name is IO, then specify the signal name as IO.VDD for the VDD net.
  • start=start_time
    Specifies the start time from which the current will be written in the current file.
  • cycles=number_of_cycles_for_this_measure
    Specifies the number of clock cycles to be captured in the current file. By default, one cycle is captured.
  • intervals=number_of_points
    Specifies the number of time points or measurement intervals within a clock cycle.
  • clockcycle=clock_period
    Specifies the length of the clock cycle or the total duration for which the current information is being written in the current file. You must specify the unit.
  • method=[0|1|2][0|1|2][0|1|2]
    Specifies the method that the simulator uses in post-processing clock analysis data.
    [012] The number in the first position, (0), specifies the method of peak current calculation.
    [012] The number in the second position, (1), specifies the method of average current calculation.
    [012] The number in the third position, (2), specifies the method of RMS current calculation.
    0: Reports the maximum out of each interval over all periods.
    1: Reports the average out of each interval over all periods.
    2: Does not calculate peak, average, or RMS current.
    The default is 212, which is average current calculation.
  • filename=filename_prefix_for_this_measure
    Specifies the prefix for the current files that are being generated.
    
    For Voltus-Fi-XL, ensure that the prefix provided is “vps”. For example, your filename could be vps_VDD.ptiavg.
  • termflag [0 | 1]
    Specifies the terminals which will be output. Specify 0 to output the first three terminals. Specify 1 to output all the terminals.
  • Namemangling
    Specifies namemangling. When set to 0, specifies that names should not be mangled.
    Here is an example of this command.

    uti0 uti signal="IO.VDD" start=0n cycles=1 intervals=133 clockcycle=2ns method="212" filename="vps" termflag=0 Namemangling=0

• In the Spectre input emir conf file, specify eisopt save_gnd_caps=1 to include the grid capacitances in the EMIR database so that they can be used in power-grid flow. For example:
  

  net name=[I0.*] analysis=[iavg irms vmax vavg]

  eisopt save_gnd_caps=1

  emirutil autorun=[true]

The following table shows the required inputs for generating power-grid views in Voltus-Fi-XL.

The following diagram illustrates the flow of PGV generation in Voltus-Fi-XL:

Open Access (OA)-Based Library Generation

Voltus-Fi-XL lets you specify an OpenAccess (OA) database for PGV Generation. You can either specify the LEF technology file/Macro LEF file or the OA libraries. The OA library files contain information from both the LEF technology file and the Macro LEF file.The layer map file is automatically created from the specified OA file. Alternatively, you can specify the layer map file.

In the GUI, the OA libraries can be specified in the OA Libs field of the Create Power Grid Views form. This is shown in the subsequent section.

In batch mode, the OA library can be specified by using the -oa_lib parameter of the create_pgv command. The OA library should have the abstract or layout view to read the required LEF pin information. By default, the tool reads only the abstract view from the macro OA database. If the abstract view is not present, you need to specify the layout view in the LibGen command file specified with the PGV command file.

To specify the layout view:

1. Include setvar oa_layout_view_name layout in the LibGen command file: create_pgv -libgen_cmd_file cmd_file_name
2. Include this command file in the libgen_pgv.cmd file (LibGen-generated command file in the PGV directory).

Automatic Generation of Layer Map Files

The PGV flow in Voltus-Fi requires the following layer map information:

• LEF layer map file: Provides the mapping between the LEF layers and layers in the technology file.
• PGDB layer map file: Provides the mapping between the xDSPF layers and layers in the technology file.

These layer map files can either be specified in batch mode and the GUI. However, if not specified, the software generates these files for PGV generation.

Automatic Generation of the LEF layer map File

The following parameter of the create_pgv command is used to specify the LEF layer map file:

create_pgv -lef_layer_map filename

The above parameter is optional. If specified, the software uses the specified layer map file for running the PGV flow. If not specified, Voltus-Fi automatically generates the LEF layer map file.

The PGDB layer map file provides a mapping between the DSPF layer names that are written in the simulation database and the technology file layer names. Multiple DSPF layers can be mapped to one technology file layer.

The following parameter of the create_pgv command is used to specify the PGDB layer map file:

create_pgv -pgdb_layer_map pgdb_layermap_file_name

To generate the layer map file automatically, do not specify the above option. In this case, the software generates the PGDB layer map file with the name, “VFI_generated_pgdb_layer_map.txt”.

An example of the *LAYER_MAP section for a third-party DSPF file is shown below:

*LAYER_MAP

*0 SUBSTRATE

*1 AP      ITF=AP

*2 M0_A    ITF=M0

*3 M0_B     ITF=M0

*4 M1_A     ITF=M1

*5 M1_B     ITF=M1

*6 M0_A_SRM_SP   ITF=M0

*7 M0_B_SRM_SP    ITF=M0

*8 M0_A_SRM_2P    ITF=M0

*9 M0_B_SRM_2P   ITF=M0

*10 M1_A_SRM_SP   ITF=M1

An example of the *LAYER_MAP section for a Quantus DSPF file is shown below:

*LAYER_MAP

*0 none

*1 M4

*2 M3

*3 M2

If the software issues a warning message during the auto-generation of the layer map file, such as the one shown below, it means these layers are not mapped in the VFI-generated PGDB layer map file. In this case, add these layers manually in the file.

Warning: The following layers from dspf are missing in the pgdbLayerMap file specified. Please add these layers in pgdblayermap file. Missing layers may cause connectivity problems in PGV creation for the net VDD.

mwires bwires

If there are no warnings, the VFI-generated PGDB layer map file can be used for running the PGV flow without making any changes.

Generating Power-Grid Views in Voltus-Fi-XL

Voltus-Fi-XL creates PGVs for both static and dynamic rail analysis. It creates PGVs for static rail analysis along with the PGVs for dynamic rail analysis by using the average values of the current waveforms. However, it does not create PGVs only for static rail analysis.

To create power-grid views in Voltus-Fi-XL, perform the following steps:

1. In the Voltus-Fi-XL console, choose IR/EM Analysis – Create Power Grid View.
   The Create Power Grid Views form opens, as shown below.
   
   
2. .Specify the OA database library.
   If this option is specified, you do not need to specify the Tech Lef File/Macro Lef File options.
3. Specify the Macro Name and Library Name.
4. Specify the Extraction Tech File, Tech Lef File, and Macro Lef File.
   In case the technology data and design data are in the same LEF file, use any of the two options, Tech Lef File or Macro Lef File to specify the filename.
5. Specify the Lef Def Layer Map File and PGDB Layer Map File.
6. Specify the Simulation Directory.
7. Specify the Simulation Prefix. This input is optional.
8. Specify the UTI Ron File generated by Spectre.
   If this file is not specified, Voltus-Fi-XL uses the Ron values from the MMSIM simulation database (*.emir#_bin file).
9. Specify the Trigger File, Net Name, and the corresponding Voltage.
10. Specify the State Directory / Results File.
    The naming convention of the simulation result file is, *.emir#_bin. For example, your result file could be named, xps.emir0_bin.
11. Click Add to add the net, the corresponding voltage, and the EMIR Results DB file location to the list.
12. In the Output group box, specify the Results Directory.
13. Click OK.

The following output is obtained after generating PGVs in Voltus-Fi-XL:

• A binary database that contains geometric views of the cell, port information, and the power-grid views.
• Text report and summary file with detailed information about the power-grid views.

The output of PGV generation in Voltus-Fi-XL is used in Voltus for dynamic power calculation and static and dynamic IR drop analysis.

Troubleshooting Information for PGV Generation in Voltus-Fi-XL

After generating the PGVs in Voltus-Fi-XL, you can check whether the PGVs are correctly generated or not. Listed below are a couple of issues that you may encounter while generating PGVs, and the information to help resolve them.

• No current information in the PGVs
  If there is no current information in the PGVs, check your log file for a warning titled, VOLTUS_LGEN-3065. This warning is issued when there is a mismatch between taps in the current files and the simulation database. If all taps fail, the current value in the PGV will be zero. To check the names and number of taps in the current file, you can use Itaputil. Itaputil is a Cadence utility that either reports characteristics of tap current files or extracts portions of the data and places them into a new tap current file.
  For example, if your current file is vps_VDD.ptiavg, you can use the following command to list the names of all the taps in this file:
  itaputil list vps_VDD.ptiavg > names
  
  To get help on the complete list of available commands in Itaputil, type the following in the xterm or shell:
  itaputil -h
• The current file does not have any waveforms
  If the current file does not have any waveforms, it could be because of an error in the UTI command used for generating the current file. For resolving this issue, use Itaputil to check the tap names in the current file and to write the current data in the file.