Block Placer Form

Use the Block Placer form to automatically place all hard and soft blocks in a design and minimize the wire length and chip area. The Block Placer form contains the following tabs.

Tab	Description
General Tab	Lets you define the chip dimensions, cost order, and other options
Constraints Tab	Specifies the constraints that the block placer has to use to converge on a solution.

General Tab

The following table describes the fields available on the General tab of the Block Placer form.

Field	Description
*Chip Dimensions*	This section provides the chip dimension options.
Fixed Die	Specifies that the block placer cannot alter the chip dimensions. This option is selected by default if the boundary area constraint is unavailable in the design. This option is selected by default if Boundary Area constraint is unavailable in the design. However, if Boundary Area constraint is available, the Fixed Die option is deselected. The block placer runs in the variable die mode and can alter the chip dimensions, if required, to place the blocks. Block placer always runs in Fixed Die mode if any of the following is true: Design boundary is rectilinear in shape. The coreBoxSpec or IO box attributes of PR boundary are present. Design contains IO rows. If Fixed Die is selected, Specify Chip Dimension Range is not available. The value you specify in this field is retained when you restart block placer.
Minimum I/O to Core Distance	Specifies the distance between the IOBox and the coreBox (the spacing between the pads and the blocks). The default value is the maximum value of `minSpacings` of routing layers across all layer purposes. This option is available only when there are IO pads in the design. The value you specify in this field is retained when you restart block placer.
Minimum Boundary to Instance Distance	Specifies the minimum distance between the design boundary and instance edge. This option is available only when there are no IO pads in the design and takes the top-level rectilinear boundary into account. The default value is the sum of the maximum value of `minSpacings` of routing layers across all layer purposes and the largest pin size in the design. The block placer retains the value you specify in this field when you restart block placer in the same Virtuoso session.
Specify Chip Dimension Range	Specifies the method that you want to use to define the dimensions of the chip. The initial value is populated from the values specified in the `areaBoundary` constraint in Constraint Manager. The above fields are available only if Fixed Die is not selected. The values you specify in these fields are retained when you restart block placer. Width and Height: Activates the PRBoundary Width Range and PRBoundary Height Range options. PRBoundary Width Range: Specifies the minimum and maximum width of the chip. PRBoundary Height Range: Specifies the minimum and maximum height of the chip. Area and Aspect Ratio: Activates the PRBoundary Area Range and PRBoundary Aspect Ratio (W/H) Range options. PRBoundary Area Range: Specifies the minimum and maximum area for the design boundary. The area range is calculated from the `boundaryArea` constraint as follows: minimum area = minimum width * minimum height maximum area = maximum width * maximum height PRBoundary Aspect Ratio (W/H) Range: Specifies the minimum and maximum aspect ratio for the design boundary. The aspect ratio range is calculated from the `boundaryArea` constraint as follows: minimum aspect ratio = minimum width / maximum height maximum aspect ratio = maximum width / minimum height
*Cost Order*	This section provides the order that the block placer has to follow to minimize cost. The cost with the highest priority is minimized first.
Default Cost Order	Restores the original cost order.
Overlap	Specifies the cost used to minimize overlap between the blocks placed by block placer. If block placer is unable to place blocks without overlap, the information is displayed in the log file and the CIW.
Boundary	Specifies the cost used to place all the blocks within the design boundary. If the design core area is insufficient to accommodate all the blocks, block placer will generate a solution with some overlap.
Order	Specifies the cost used by block placer to align the blocks.
Distance	When this cost is used, block placer ensures that the minimum distance between the blocks and minimum distance between boundary and instance is maintained.
Net Length	Specifies the cost used by block placer to minimize net length. The net length is calculated based on the steiner net length estimation.
Cluster	Specifies the cost used by block placer to place together all the blocks belonging to a particular cluster.
Cluster Boundary	When this cost is used, block placer places all the instances belonging to the cluster (corresponding to the cluster boundary) within the cluster boundary. Block placer treats the cluster boundary as inclusive cluster boundary i.e. it can contain instances that do not belong to the cluster.
Net Criticality	Specifies the cost to ensure proximity of blocks connected by nets of high criticality. It also takes into account the connectivity between the placed, fixed, and locked pins.
Halo	Specifies the cost used to ensure that no block should be placed on the placement halo. Halos are treated as placement blockages. If there are no area halos around the blocks and there is no minimum distance constraint, then the blocks are abutted.
*Options*	This section provides the placement options.
Default Minimum Distance between Instances	Specifies the default minimum distance between instances or virtual hierarchies. You can also override this value for any instance pair through the Constraints tab. In Layout EXL, the option can be used to control the spacing between virtual hierarchies, if present in the design. The value you specify in this field is retained when you restart block placer. User Defined: Lets you define the distance between the instances or virtual hierarchies by specifying a value. Pins per Side: Enables the default value when this option is selected and calculates using the following formula: spacing = [total number of pins/number of sides of block] X [max of `minWidth` of layer across all layer purposes + max of `minSpacing` across all layer purposes`]`.
Optimize Top-Level Pins	Specifies whether the block placer has to optimize the top-level pins after block placement. However, the soft block pins are not optimized. The value you specify in this field is retained when you restart block placer. When block placer is run on variable die mode, the top-level pins are made floating. However, if Optimize Top-Level Pins is selected, the pins are placed accordingly. When Optimize Top-Level Pins is selected, Block placer does not consider the top-level pins with Placed status as blockages. If Optimize Top-Level Pins is not selected, then the top-level pins with Placed status are considered as routing blockages and allows the block placer to place blocks and avoid shorts with already placed pins.
Effort	Specifies the effort that block placer should make before arriving at the possible solutions. The minimum allowed value is `1` (least effort) and maximum allowed value is `5` (maximum effort). The default value is `3`.
Number of Solutions	Specifies the number of solutions that you want block placer to generate. The minimum allowed value is `1` and maximum value is `5`, which also provides the best results. The default value is `3`. By default, block placer loads the best solution.
Enable Multi Threading	Reduces the time taken by the block placer to place a large number of macros. In addition to the number of macros, the placement time depends on the design connectivity, constraints, and machine configuration, such as the number of cores and CPUs. If these parameters are kept constant, then enabling multi threading should result in a 2x performance improvement.
Enable Congestion Based Refinement	Enables only if congestion data is available. When this field is enabled, the congestion value is taken into account during block placement. Congestion Value: Lets you specify the congestion threshold value. For example, if you specify the threshold value as 80, block placer will try to reduce the congestion in all areas in the design that have a congestion above 80 percent. If you are placing blocks in the congestion based refinement mode, you should also optimize the top-level pins for optimum results. If you do not optimize the top-level pins while running block placer in the congestion based refinement mode, a message is displayed in the CIW. Fixed pins at the top level are not moved when you optimize the top-level pins. After congestion-aware block placement, if you click Undo, the congestion and global route data may still remain. In such a situation, run the global route and congestion analysis on the design to retrieve the congestion data.
Number of Iterations	Specifies the maximum number of iterations that can be performed between the congestion-based refinement block placer and the Global Router to bring congestion within the limits. The congestion limit is specified in the Congestion Value field. Specifying the number of iterations improves the quality of congestion based refinement block placer and reach satisfactory congestion level. By default, Number of Iterations is disabled. This option is only enabled when Enable Congestion Based Refinement field is selected.

Constraints Tab

The following table describes the fields available on the Constraints tab of the Block Placer form. The Constraints tab has the following sub tabs:

Soft Block Constraints
Instance Constraints

Relative Constraints

Field	Description
*Soft Block Constraints*	This tab provides the side constraints for soft blocks.
Soft Block Size Constraints	Lists all the rectangular and rectilinear soft blocks in the design cellview.
Library, Cell Name, and View Name	Specifies the read-only fields that depict the library, cell name and view name of the soft block.
Resize	Indicates if block placer can modify the boundary of the soft block. The default value is False. If you modify the Resize field for a rectilinear soft block to True, block placer resizes the soft block, converts it to a rectangular soft block, and displays an appropriate message for soft block resize in the log file.
Area	Specifies the area of the selected soft block.
Minimum AR and Maximum AR	Specifies the minimum and maximum aspect ratio of the selected soft block. If the Area, Minimum AR, and Maximum AR fields for a soft block are empty, it means no corresponding constraints exist. In this case, block placer resizes the soft block without any aspect ratio constraint to optimize space.
Update All	Applies changes to all soft blocks.
Update Selected	Applies changes to only the selected soft blocks.
Reload Constraints from Constraint Manager	Reloads constraint values from the Constraint Manager.
*Instance Constraints*	This tab provides the instance constraints for soft blocks.
Instance To Instance Edge Distance	Specifies the distance constraints between any two instances. Instance to Instance Distance: Populates the table from the Instance to Instance Distance constraints present in the Constraint Manager. Instance1 and Instance2: Lists all the instances in the design. You can select the instances on which the minimum and maximum distance constraint are to be applied. Minimum and Maximum: Specifies the minimum and maximum edge-to-edge distance values.
Instance To Boundary Distance Constraints	This section specifies the distance constraints between an instance and the design boundary. Instance to Boundary Distance: Lists all the Instance to Boundary Distance constraints present in the Constraint Manager. Instance Name: Lists all instance names in the design. Minimum Distance and Maximum Distance: Specifies the minimum and maximum instance-to-boundary distance values from the design boundary. The initial values of are populated from the Distance constraint in the Constraint Manager. Boundary Edge: Specifies the edge to which the constraint is to be applied. The valid values are Left, Right, Top, and Bottom. Reload Constraints from Constraint Manager: Reloads constraint values from the Constraint Manager. Filter: Enables you to filter the instances in the Instance Name list box.
*Relative Constraints*	This tab provides the order and alignment constraints to be applied.
Order/Alignment	Lists the alignment constraints to be applied. This table is initially populated with all the existing Alignment constraints present in the Constraint Manager.
Reference Instance	Specifies the reference instance for calculating the order and alignment. It lists all the instances in the cellview. You can select only one instance from this field to add and update a constraint. If you select a row in the constraints table, the corresponding reference instance value is highlighted in this field. Filter: Enables you to filter the instances in the Reference Instance field.
Alignment Side	Specifies the edge for which the constraint is to be used for alignment. The possible values are Left, Right, Top and Bottom. If you select a row in the constraints table, the corresponding alignment side is highlighted in this field.
Relative Position	Specifies the relative position of the target instance with respect to the reference instance. If you do not want to specify a relative position, you can specify the values as None. If you select a row in the table, the corresponding relative position value is highlighted in the Relative Position field. However, if you select multiple rows, the Update field is grayed out.
Target Instances	Lists all the blocks that can be aligned with the reference block and the order in which they would be aligned. You can specify the order in which the blocks should be aligned by using the arrow buttons on the right of this field. Clicking the up arrow button places the blocks closer to the referenced instance. Similarly, clicking the down arrow button places the blocks away from the referenced instance. You can also remove the instances from the constraint by moving them to the All Instances box. You can also add target instances by selecting an instance from the All Instances box and using the up arrow button placed above the All Instances box. If you select a row in the table, the corresponding target instances are highlighted in the Target Instances field. However, if you select multiple rows, Update field is grayed out.
All Instances	Lists all the instances in the design except the fixed and locked instances. You can select multiple instances in this field and move them to Target Instances by using the up arrow button. Filter: Enables you to filter the instances in the All Instances field.
Add	Creates a new constraint.
Update	Modifies the selected constraint.
Delete	Deletes the selected constraint.

Virtuoso Floorplanner User Guide
Product Version IC23.1, November 2023

Block Placer Form

General Tab

Constraints Tab

Related Topics

Virtuoso Floorplanner User GuideProduct Version IC23.1, November 2023

Block Placer Form

General Tab

Constraints Tab

Related Topics

Virtuoso Floorplanner User Guide
Product Version IC23.1, November 2023