DESIGN VIEWPOINT EDITOR

Design Viewpoint Editor is used to create special purpose "variations" or "viewpoints" of a schematic. Viewpoints allow you to rapidly adjust and maintain different sets of properties for your schematic independent of the graphical drawing. You can maintain variations of a schematic without having to go back and re-edit the drawing for each one. Viewpoints allow you to save and maintain various experimental setups for a schematic without having to create a new one for each experiment. The use of viewpoints also allows several engineers to work with the same schematic drawing concurrently without having to maintain multiple identical copies of it.

Design Viewpoint Editor can be used to set local properties of parts in a schematic as well as global parameters which pertain to the whole drawing. It can also be used to set up standard configurations for using the drawing as input to other design tools such as simulators and layout tools. Here we will use Design Viewpoint Editor to set the parameters needed to simulate our design using scn08hp standard cells for MOSIS fabrication. This will be done by customizing a generic QuickSim simulation viewpoint to work with the scn08hp library. The customization is quite straightforward as it requires only the addition of one primitive model and one electrical properties parameter. For more details regarding primitives and parameters, see Design Configuration Rules on page 2-4 of the Design Viewpoint Editor User's and Reference Manual in the INFORM database.

1. You first begin by invoking Design Viewpoint Editor either by clicking on its icon in the Design Manager tools window or by typing dve at the unix command line prompt. The application window should appear similar to that shown in Figure 4.

   
   Figure 4: Design Viewpoint Editor Window.

2. Click on the OPEN VPT button, then open the navigator window. Select the component you want to create a viewpoint of (in this case, the 2-1 mux) and click OK.

3. In the Open Design Viewpoint dialog box, change the viewpoint name from default to some easily recognized name. Use qsim_nom in this example, since our intent is to simulate the circuit with nominal delays for the logic gates. Click OK. Two windows will open, with one having the name of the current viewpoint and the other titled Design Configuration.

4. Even though we are targeting QuickSim II in this tutorial, a variety of design tools can be used with your schematic. Each tool has specific requirements for properties and values which are associated with the components in the schematic. We will now start the viewpoint setup for our scn08hp parts with the primitives and properties needed for QuickSim. Select the standard setup (Quick)SIM and Path from the Setup menu in the menu bar. Another way to do this is to click on the SETUP VPT icon in the Setup palette. Your screen should now look something like this

5. You will now customize the standard viewpoint with two additions. First, you establish that any part having the model property value of "technology" will be considered a primitive in the design hierarchy: in other words, a leaf of the hierarchy tree.

   From the Edit menu bar, select ADD -> PRIMITIVE, or, simply click on the ADD PRIM icon in the Setup palette. Enter the following values into the form which appears:

   Name: model
   Value: technology
   Property Type: Expression
   

   This also specifies that the property value "technology" will be treated as an expression: in this case as a single variable expression to be evaluated wherever it is specified. Click on OK when done.

6. You now need to specify a value for the variable parameter "technology" which appears in the above model expression.

   From the Edit menu bar, select ADD -> PARAMETER, or simply click on the ADD PARAM icon in the palette. The values required in this form are:

   Name: technology
   Value: scn08hp_nom

   This tells DVE to give the variable parameter "technology" the value "scn08hp_nom". Now when simulating from this viewpoint, the delay properties associated with nominal operation of these cells will be used. No further schematic editing needs to be done to enter gate delays, because the "scn08hp_nom" delay tables which come with the cell library will be used. Your screen should now look like this.

7. Save the viewpoint by clicking on the SAVE DESIGN icon and exit DVE.

Alternatively, you can use the script qsim_prep for creating the Quicksim viewpoint with the specific setup for the scn08hp_nom library of standard cells. In order to run this script, you have to first add the directory in which it is located in your UNIX "path". To create a viewpoint, then, just go to the directory where your logic design is rooted, and run qsim_prep design_name, where "design_name" is the name of your logic design. The name of the created viewpoint will be by default qsim.vp.

You have now created a design viewpoint which attaches to the basic 2-1 MUX schematic all the necessary parameters for simulating the part using scn08hp standard cell models under nominal delay conditions. This standard library is also set up to simulate under worst case delay conditions (set "technology" to "scn08hp_slow") and under best case delay conditions (use "scn08hp_fast"). You may want to create different viewpoints for each of these additional cases, or simply edit the existing viewpoint using DVE. You may later want to consider how you would set up a viewpoint to simulate different parts of the same design using different delay conditions. For the moment, you are ready to learn how to use QuickSim II in combination with a custom design viewpoint to simulate the 2-1 MUX.