This panel specifies a path to a layout or saved Cell Hierarchy Digest (CHD) file, from which a new CHD will be created in memory and added to the Cell Hierarchy Digests listing. The panel is brought up with the Add button in the Cell Hierarchy Digests panel.
The panel provides two separate ``notebook'' tabs that specify the type of file to read: layout file or saved CHD file. The notebook pages expose the controls applicable to the type of input, however either type of file can be entered in the entry area of either page. The tabs serve to simplify the panel.
All cell hierarchy data, both physical and electrical, will be extracted from a layout file. However, if the LockMode variable is set while in physical mode, the electrical data, if any, will be omitted. If the source is a saved CHD file, the CHD in memory will be recreated verbatim, ignoring current mode settings.
When the source is a layout file, systematic cell name modifications can be applied, if desired. This is sometimes useful for avoiding name clashes. If cell name modification is used, the modified names must be used when specifying a cell to the new CHD, the original cell names are not retained.
When reading a layout file, it is possible to save some statistical information in the CHD, regarding counts of the geometrical objects in the file. This information will increase the size of the CHD in memory, with the bottom selection requiring the most memory, the top selection the least. The information saved is counts of the number of boxes, polygons, and wires seen. The choices are:
This information will be printed in the Info window of the Cell Hierarchy Digests pop-up. The file totals are shown in the CHD info, which is shown when there is no selection in the Contents window. The per-cell counts are shown in the Info window when a cell name is selected in the Contents listing.
If the CHD is going to be used in an operation with layer filtering, it is recommended that per-cell and per-layer counts be selected, as this allows efficient removal of cells made empty by the layer filtering (see 14.10).
If the file name specified is a saved CHD file (previously created from the Save button in the Cell Hierarchy Digests pop-up), then the other entries (cell name mapping and geometry counts) are ignored. The cell name mapping is retained from the original CHD that was saved. The geometry counts are presently discarded when a CHD is saved.
If the CHD file being read contains geometry records, the processing of these records can be specified by the radio buttons in the CHD file page. There are three choices. The first option is to create a memory-type CGD from the geometry records, and link it to the CHD. In this case, all geometry data will reside in memory, which makes sense even for very large designs as the data are highly compressed. The second option is to create a file-type CGD and link it to the CHD. In this type of CGD, geometry is obtained from the geometry records in the CHD file when needed, and does not reside in memory. The third option is to ignore the geometry records, and therefor not create a linked CGD. Geometry will be obtained from the original layout file in this case (the original layout file must still exist in the same location as when the CHD file was created).
These options are identical to default options which can be set from the Cell Hierarchy Digests panel, but the present panel overrides the default setting and applies only to the current operation.