Gradrat - What you really need to know: EE edition¶

When editing a schematic in Cadence you can (should) add in a built-in sheet element border to each schematic view:

Edit->Sheet Size...

If you want to customize what is displayed, you can change the contents by editing (as the CAD/root user) the Asize/Bsize symbol views in the US_8ths library AND the Title symbol view.

Some possible labels to add include:

ilInst~>cellView~>cellName

This provides the name of the cell that the sheet is instantiated in.

SosGetCurrentVersion(ilInst~>cellView)

If you are using Cliosoft, this provides the revision/managed state of the cellview.

ilInst~>cellView~>fileTimeStamp

This provides the last date/time that the schematic was edited & saved.

ilInst~>cellView~>createTime

This provides the creation date for the schematic.

if(ilInst~>cellView~>modifiedButNotSaved then “True” else “False”)

Indicates whether the schematic has been modified but not saved.

dbGetPropByName(ilInst~>cellView “lastSchematicExtraction”)~>value

This returns the date that the schematic was last “checked”.

• To change how Cadence marks connectivity on nets, you can choose Connectivity–>Nets–>Mark and then hit the F3 button for options
• To preset certain options for yourself, you can modify your .cdsenv file. For example, to choose which layers you want excluded in the connectivity you could add:

layout markNetExcludePurposes boolean t
layout _markNetExcludePurposesName string "boundary annotate error label flight warning"

• You can also save the mark net options from the options form that appears when you hit F3. If you save this to the tech library, then those options become the default for all libraries that use that tech lib. The file should be saved with the name markNetOptions and placed in this path:

<tech library directory>/.cadence/dfII/markNet/markNetOptions

This will be the default file if there isn’t a similar path in the current directory (where virtuoso was launched) or in the user’s home directory.

Multipart paths can be useful for things like creating guard rings or seal rings or any connected structure that requires relative spacings/sizings.

1. Open a layout view
2. Go to Create->Multipart Path
3. Hit the ‘F3’ key to bring up the Multipart Path options menu
4. Choose a template name to create or edit
5. Click the Subpart... options button to create the multipart path definition

Depending on how you normally define pin/net connectivity, you sometimes may want to create pin database objects from text labels so that the layout can be better used in subsequent layouts in tools such as Layout-XL.

• If you are using labels (on layers M1TXT, M2TXT, etc.), go to the Tools menu and select Create Pins from Labels....

• A window will pop up with options to put pins on locations of labels.

• The default settings should be:

  • Objects Within: Cellview
  • Object Type: Both
  • Objects: All

• If you just have M3TXT labels, then make sure to check the ignore checkbox on the right of all the other ones. If you have M2TXT, then make sure to not ignore those, etc.

• The column with Objects Layer is where it is looking for the labels. The Pin Layer is where it will add a rectangular pin.

• For something like M3TXT, you should change the Pin Layer to M3, etc.

• After pressing OK, there will be little metal rectangles at every label. You may have to go to each one to make sure they are all at the appropriate places (and not producing DRC errors).

Sometimes you will want to do this if the layout is intended to be used in an automated place & route tool or perhaps for estimating a design size in Layout-XL.

1. Go to the Create menu and select P&R Objects and then P&R Boundary.
2. Point to the two opposite corners of the boundary of your cell and then adjust the shape by chopping, etc, if needed.

The PVS menu is not available by default in Cadence. To make it available, you should:

1. Open the layout view of a cell
2. Go to Launch->Plugins->PVS in the cell view’s menu
3. Now a PVS menu item should be present in the layout cell view

To get the PVS menu to appear by default when you open a layout view, you should add the following lines (or similar) to your .cdsinit file.

printf( strcat("-- Registering PVS menu triggers... \n"))
deRegUserTriggers("maskLayout" nil '_pvsMaskLayoutMenuTrigger)
deRegUserTriggers("maskLayoutXL" nil '_pvsMaskLayoutMenuTrigger)

The first line, is just informational for users. The next two lines launch PVS whenever Layout, or LayoutXL tools are used.

To create/populate a DRC/LVS preset file:

1. Launch the DRC or LVS menu from the PVS menu PVS->Run DRC.. (or PVS->Run LVS..)
2. Fill out the Run directory, inputs, rule files, etc...
3. Save the settings for the run by choosing the File->Save Presets option from the DRC/LVS run menu

Once you have a presets file, you can simply:

1. Open the DRC or LVS run menu
2. Go to File->Load Presets

The tool is somewhat smart about replacing some of cell specific preset options with the current cell (e.g. input cell, output netlist/files, etc...).

To have a specific preset file loaded by default (e.g. if several users all want to use the same preset file), simply define the following environment variables:

setenv PVSUI_LVS_PRESETS_FILE <path to lvs preset file>
setenv PVSUI_DRC_PRESETS_FILE <path to drc preset file>

We can define a PVSPreFormTrigger to customize certain components of the LVS/DRC menu. An example of this procedure is provided below.

procedure( PVSPreFormTrigger(runType presetFile winId)
    let(
        (projDir user
        pvsTechLibPath
        runDir runDirExt
        cv cellName libName
        tmpFile f
        )

        cv = winId~>cellView
        user = getShellEnvVar("USER")
        projDir = getShellEnvVar("PROJECT")

        pvsTechLibPath = strcat( projDir "/cad/cds.lib")

        runDirExt = case(runType
                ("LVS" "lvs")
                ("DRC" "drc")
                ("FASTXOR" "fastxor")
                ("XOR" "xor")
                (t 'default)
            ); case

        cellName = cv~>cellName
        libName = cv~>libName
        runDir = strcat("/tmp_ssd/" user "/pvs/" libName "/" cellName "/" runDirExt)

        ; Write out the temporary presets file
        tmpFile = makeTempFileName( strcat(getTempDir() "/pvs"))
        f = outfile(tmpFile)
        fprintf(f "[ pvsgui.Run%s ]\n" runType)
        fprintf(f "RunDir \"%s\" \n" runDir )
        close(f)

        ; Return the name of the presets file
        tmpFile

    ); let
); procedure

This procedure re-defines the run directory based on the cell’s name and library. If a preset file is loaded in conjunction with this procedure, the “smart” part of the tool automatically changes several other form inputs based on the run directory while keeping things like the rule file and tool options the same.

The output of the cds_qrc_techgen process is a technology directory(ies) that corresponds to a particular process corner/option. This technology directory should appear as rule or corner when running parasitic extraction (PVS->Quantus QRC). To do this, you need to provide a path to that directory by defining a corner.defs file in the tech library path which might look like:

DEFINE TYP <PATH TO typical corner QRC run directory>
DEFINE SLOW <PATH TO slow corner QRC run directory>
DEFINE FAST <PATH TO fast corner QRC run directory>

When we want to run extraction based on a PVS-LVS run, we can use the PVS->QRC flow by launching the tool in the layout tool menu: QRC->Run PVS-Quantus QRC...

This menu can be automatically populated by (re)defining the vuiUserDefinedRCXFormSetupCB skill procedure. An example of that procedure is shown below:

procedure( vuiUserDefinedRCXFormSetupCB(form)
    let(
        (projDir user
        pvsTechLibPath pvsTechLibName
        lvsRunDir svdbQRCDir
        cv cellName libName
        )

        cv = geGetWindowRep()
        user = getShellEnvVar("USER")
        projDir = getShellEnvVar("PROJECT")

        pvsTechLibPath = ddGetUpdatedLib()
        pvsTechLibName = "QRC_LIB"

        cellName = cv~>cellName
        libName = cv~>libName
        lvsRunDir = strcat("/tmp_ssd/" user "/pvs/" libName "/" cellName "/lvs")
        svdbQRCDir = strcat( lvsRunDir "/svdb" )

        ; Setting of the preQRCform
         when( form->hiFormSym == 'vuipreRcxForm
             form->runName->value = cellName
             form->runDir->value = svdbQRCDir
             form->assuraTech->value = pvsTechLibPath
             form->tech->value = pvsTechLibName
        ); end of when preQRC

        ; need to return a true for the QRC run to continue
        t

    ); let
); procedure

In this example, the cds.lib used to define the libraries is provided as the lib path definition for the tool. It also defines the run directory in the same way as the DRC/LVS example above.