Assisted Placement of Devices

Assisted placement refers to the manual adjustments done to placed device instances after running Virtuoso Placer. Assisted placement is generally done to improve device placement as per your design requirements.

Assisted placement commands are available in the Place menu. These commands support transparent group mode, in which you can edit individual members of user-defined groups.

Before moving devices using the assisted placement commands, in the Display Options form, set the Show Name Of option to instance or both.

Guidelines for running the assisted placement commands are:

Start with assisted move to group devices with similar masters and similar finger lengths. No device should be adjacent to another dissimilar device.
Ensure that the devices are ordered top to bottom in a manner that maintains the path of the current from the power rail to the ground rail.
After you have grouped devices by type, run the required assisted placement commands to improve placement.
Press Ctrl+D to deselect all devices, and then carefully select only the ones you need before running an assisted placement command.

The following assisted placement commands are available in the Place menu:

Resolve Overlaps	Resolves overlaps between devices in rows to remove any shorts that are created when you move the devices or snap them to rows.
Abut Instances	Abutting devices helps avoid loss of area consumed by the extra poly fingers on either side of each device. You can abut selected or all instances in a design. If there are no instances selected before running the command, all instances in the design are abutted. The Placement Options form includes the Abut Rows Use Device Order option, which specifies whether abutment should follow the order in which instances were placed in each row.
UnAbut Instances	Unabuts selected instances in the design. If no instances are selected before running the command, all instances in the design are unabutted.
Swap Instances	Swaps the positions of the selected instances, chains, and figGroups. The locations of the selected instances are switched but their orientations are retained as in their initial position.
Swap Rows	Swaps components of the rows that contain the selected instances, chains, or figGroups. Contents of the two rows have to be compatible to be swapped to the new row. Boundary cells are ignored during row swapping. Locked instances, highlighted in red in the design canvas, are also ignored.
Snap to Grids/Rows	Snaps instances to their nearest compatible rows in a Spacing Pattern (SP) or Width Spacing Patterns (WSP)-correct manner. This option is intended as a batch alternative to the assisted move commands.
Adjust PR Boundary	Adjusts the PR boundary to enclose all placed instances. Unused rows are deleted, unused space is chopped, and the PR boundary is adjusted accordingly without disturbing the placement.

Swapping Instances

Use the Swap Instances assisted placement command to swap positions of the selected instances, chains, or figGroups.

Choose Place—Swap Instances.
Click the first instance to be swapped.
Click the second instance.
You can also select the components first and then choose Place—Swap Instances. After selecting the command,
Press F3 to display the Swap Components form.
Select a position from the Swap Origin list to specify the position to which the instance needs to be moved. This option is useful when there is a difference in the sizes of the instances to be swapped.
Select Resolve Overlaps to automatically resolve overlaps while placing the devices at their new locations.
Select Fix swapped objects during overlap resolution to ensure that the position of the swapped device is not changed while resolving overlaps.
Click Hide to run the command on the selected instances.

The locations of the selected instances are switched, but their orientations are retained as in their initial position.

Support for Transparent Group Mode

The assisted placement options support the transparent group mode. In this mode, you can select and edit individual members of user-defined groups at the top-level, while retaining them as members of their respective groups. You can edit objects in nested groups also at the top-level, without performing multiple Edit In Place operations. With Resolve Overlaps selected, the user-defined group instances that are at the same level as the selected member instance interact as individual members. Other groups, which are at the same or different levels, behave as groups.

Virtuoso Placer User Guide
Product Version IC23.1, March 2023