The Config button in the Cell Hierarchy Digests panel brings up the Configure Cell Hierarchy Digest panel, with which it is possible to change the default top cell of a Cell Hierarchy Digest (CHD), and to link a Cell Geometry Digest (CGD) which can accelerate geometry record access.
The present default top-level cell name is shown in the editable area near the top of the pop-up. In an unconfigured CHD, the default top-level cell is the first cell encountered in the layout file that is not used as a subcell by any other cell in the file. Any cell defined in the file can be assigned as the top-level cell of the CHD. In any operation involving the CHD when a top-level cell is not otherwise specified, the configured cell will be taken as the default.
To configure a new top-level cell, use the Contents listing of the Cell Hierarchy Digests panel, if necessary, to identify an alternate cell name. Note that this is the name after any cell name modification is applied. A cell name can be dragged from the contents listing and dropped in the entry area, or the name can be entered manually.
Pressing the Apply button in this group will complete the cell name configuration. The label of the Apply button will change to ``Clear'', and the controls in this group will be grayed. The label at the top of the panel will indicate that a top-level cell has been configured. Pressing Clear will un-configure the top-level cell, reverting to the default.
The Last button will recall the last cell name used, if any.
A Cell Geometry Digest can be linked to the CHD. In this case, geometrical data retrieved through the CHD will be obtained from the CGD, and not the original layout file. This linking can be accomplished, or removed, with the lower group of controls.
To link an existing CGD, one enters its access name into the CGD name entry area. This is the name shown in the first column of the Cell Geometry Digests listing. Pressing the Apply button in this group will perform the link, gray the entries, and the button label will change to ``Clear''. The label text at the top of the panel will indicate that the CHD is now configured ``with geometry''. Pressing the Clear button will reverse the process.
If the name in the CGD name entry area matches an existing CGD, that CGD will be linked, whatever the status of the Open new CGD check box. If Open new CGD is checked, and the CGD name is empty or a non-matching name, a new CGD will be created, and either saved under the name given, or assigned a new name by Xic if no name is given.
Pressing Apply when a new CGD is to be created will bring up the Open Cell Geometry Digest panel. This allows setting up parameters in the new CGD as needed. Pressing Apply in this panel will complete the operation, as reflected by the state shown in the Configure Cell Hierarchy Digest panel. The new CGD will be listed in the Cell Geometry Digests panel, if it is visible.
When a CGD is created in this manner, specifically for linking to a CHD, the new CGD will be automatically destroyed when unlinked from the CHD (or when the linking CHD is destroyed). One can see the CGD disappear from the Cell Geometry Digests panel when unlinked (Clear is pressed) in this case.
Please note that there is no way for the CHD to know whether the linked CHD applies to the same original layout file. Linking to a CHD produced from a completely different layout will ``succeed'', and there will be no errors even in use. As geometry is being read, if a cell is not found in the linked CGD, no geometry will be returned, and the cell will appear to contain no geometry. If is up to the user to make sure that CHD and linked CGD cell name spaces are compatible.