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Creating Groups

The hierarchical representation of your design is a result of mapping your original design; it might not be optimized for your floorplanning preferences. To make floorplanning easier, you can rearrange and regroup the design hierarchy.

NOTE

The function or connectivity of logic elements may be a reason for you to place them together as a group.

Manual Grouping

  1. In the Design Hierarchy window, select the logic that you want to group.

  2. Select the first piece of logic with the left mouse button and subsequent logic with the middle mouse button. Or, select subsequent logic by holding down the control key and pressing the left mouse button.

  3. Select Hierarchy Group, or press the F3 key.

    The Floorplanner creates a new group and assigns an arbitrary name to the group “GRP0”. The text line looks as follows.

    GRP0 “Grouped by: User” [symbol count]

    [symbol count] is the number of logic elements

    The Floorplanner labels subsequent new user-created groups “GRP1”, “GRP2”, and so on.

  4. Use the Edit Properties command to give the new group a better name.

    The newly created group occupies a position in the lowest level of hierarchy that is common to all logic that comprises the group.

The following two figures illustrate how to create a new group in the design hierarchy.

The first figure shows the four D-type flip-flops that appear in reverse video. These are the logic symbols that have been selected to form a new group.

Figure 4.4 Step 1: Select Logic for Grouping

The next figure shows the new group. The new group is named GRP0 (highlighted in reverse video). It is the first new group to be created in the design. Note that the four flip-flops are no longer part of XBL and AC4, respectively, as indicated by the new symbol counts.

Figure 4.5 Step 2: The Floorplanner Creates New Group

The Floorplanner places the new group in the hierarchy near the group XBL, the lowest level of hierarchy that is common to the four flip-flops chosen for the group. When you expand the new group, you will see that the four flip-flops are now in the new group.

The following figure shows the new group expanded. You can place this new group as a unit on the floorplan die.

Figure 4.6 GRP0 Expanded to Show Logic Elements

Automatic Grouping

It is often more convenient to group logic by common type or signal names. Creating such groups can make it easier to floorplan.

For example, you might want to make a group of all the BUFTs that have a common output enable. In this case, do the following steps.

  1. Select Edit Find.

    This command opens the Find dialog box.

  2. Select a BUFT in the Design Hierarchy window that contains the enable signal of interest by clicking the mouse on the appropriate line (on the BUFT`s instance name).

  3. In the Connections list box, select Common Enable (BUFTs, DFFs, IO).

  4. Click Find.

  5. Click Select Found.

    The Floorplanner searches throughout the design hierarchy and highlights each BUFT that meets the criteria you selected.

    NOTE

    The Floorplanner automatically expands groups that have sub-hierarchy that meet the find criteria.

  6. Select Hierarchy Group, or press the F3 key.

    The Floorplanner creates a new group and assigns an arbitrary name to the group “GRP0” (if this is the first user-created group). The text line looks as follows.

    GRP0 “Grouped by: User” [symbol count]

    [symbol count] is the number of logic elements

    NOTE

    You can also use the Hierarchy Group By command to create these types of groups.

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