The Net Selections Button: Path Selection Control Panel

The Net Selections button in the Extract Menu brings up the Path Selection Control panel. This panel enables extraction-specific selection modes for groups, nodes, and connected conductor paths (wire nets). It is separate and distinct from the normal object and subcell selection. Command buttons in the panel replace menu buttons and modes found in other commands in earlier releases of Xic, in particular the group/node selection found in the View Extraction mode, and the Show Paths and Quick Paths commands found in the Extract Menu of Xic releases 3.1.4 and earlier are now available from this panel.

There are three basic selection modes available, which are set from the top row of buttons in the panel. Similar to normal selections, one clicks on an object in a drawing window. The object must be on a visible and selectable layer. Other selection specifications as found in the Selection Control Panel apply as well. In particular, one can choose the types of objects that are selectable, and the search-up mode. In search-up mode, layers are searched from bottom to top, rather than the default top to bottom, in physical mode. This affects the conductor chosen if the user clicks over more than one conductor layer.

Select Group/Node
When active, clicking on a conducting object in the current cell in a physical window will highlight all objects of the current cell in that conductor group. In electrical windows displaying the same cell, the corresponding node connections and wires will be highlighted. Clicking on a connection point or wire in an electrical window will highlight that node, and also highlight the corresponding group in physical windows.

Physical objects are ``conducting'' if the Conductor keyword was applied (directly or by inference) to the layer of the object.

If the Select Path button is also pressed while in this mode, the conducting path, as it recurses into subcells, will also be shown in physical windows.

Pressing the p key will toggle the state of the Select Path button and the display of recursive conductor paths.

With the mouse pointer in a physical window, typing a group number followed by Enter will switch to the display of that group and corresponding node. Similarly, in an electrical window, entering a node name or number followed by Enter will switch the display to the entered node and corresponding group. However, entering a name will probably trigger all kinds of accelerators, including those for this command, so there is a trick. Type a single or double quote character, followed by the node name. The quote character will inhibit recognition of accelerators. Since the keypress buffer length is only 16 characters, long node names can't be entered in this manner, the equivalent node number can be entered or some other method used to select the node.

In electrical mode, the command works with the Node Mapping Editor when visible. The currently selected node will always be highlighted in the node list panel of the editor. Selecting a node in the editor will highlight that node/group in the display windows.

Select Path
When the Select Group/Node button is also pressed, physical windows will display the conducting path of the currently selected group descending into subcells. Otherwise, this button initiates a different command for displaying conductor paths recursively. This mode is available in physical mode only. Clicking on a conducting object will highlight the conductor path containing that object. There is no selection or indication of the corresponding electrical node, nor will clicking in an electrical window have any effect in this mode. The clicked-on object need not be in the current cell (as is required for group/node selection), but must be within the search depth. The path generation algorithm makes use of the extraction system, and observes extracted devices and exclude directives as provided to the extraction system.

Only one path can be shown at a time. Clicking on another object will rebuild a path from the second object, erasing the original path, or it is possible to select a sub-path, it that feature is enabled.

If a dark-field ground plane is used, clicking on the painted areas (holes in the ground plane) will select the ground group, as will clicking on any other object which is connected to ground (group 0).

"Quick" Path
This command is similar to the Select Path command, but does not use the extraction system, except for establishing conducting layers and connections through vias. In particular, there is no information about devices and other extraction constraints established at higher levels. It may be useful for tracing wire nets, while skipping the sometimes lengthly extraction operation.

The "Quick" Path algorithm, unlike Show Paths, will ignore layers that are set invisible.

Since extraction is not used, there is no concept of devices, so that results may not be as expected, and not be as seen with the Show Paths mode. For example, consider MOS devices. Since, the source and drain are connected to a common area of the ``active'' layer, which is (usually) a Conductor, the simple algorithm used in this mode will interpret the source and drain as being connected together, since it does not recognize the MOS device. As a consequence, all wire nets are likely shorted together in this mode!

In order to get meaningful results, it may be necessary in this case to temporarily remove the Conductor keyword from the active layer. This can be accomplished with the Tech Parameter Editor in the Attributes Menu.

The remaining buttons and controls in the panel provide options or modes while the selections are active.

"Quick" Path ground plane handling
This menu applies only to the "Quick" Path selection mode, and sets the ground plane handling method. This tracks the setting of the QpathGroundPlane variable. If a dark-field ground plane (GroundPlaneClear keyword) has been specified in the technology file, the implied connectivity to ground is similar to that in force for the extraction system. There are three choices for handling the ground plane.

Use ground plane if available
This is the default. If an inverted ground plane has already been created and is current, it will be used when determining paths. If the ground plane does not have a current inversion, the absence of the layer will imply a ground contact, as in extraction without the MultiNet keyword. This choice avoids the sometimes lengthly inversion computation, but makes use of the inversion if it has already been done. The inversion is performed during extraction.

Create and use ground plane
If the extraction system would use an inverted ground plane, it will be created if not already present and current. The path selection will include the inverted layer.

Never use ground plane The "Quick" Path mode will never use the inverted ground plane.

Search path depth
This control and associated buttons apply when the Select Path or "Quick" Path modes are in effect. It determines the depth to recurse to when the conductor path is being constructed. If 0, only objects in the current (top-level) cell will be considered. The depth can be entered directly, or by clicking the up/down buttons, or by pressing the 0 or All buttons.

While the command is active, the expansion depth can also be changed with the -, +, n, and a keys. These decrement, increment, set to 0, and set to maximum, the depth, respectively.

When the depth changes, the path, if one is being shown, will be redrawn, if possible (the original object must be above the new depth).

"Quick" Path use Conductor
If this check box is not checked, only objects on layers with the Routing attribute applied will be considered for inclusion in the extracted path. If checked, objects on layers with the Conductor attribute will be allowed. The Routing attribute implies Conductor, but may be more restrictive.

The QpathUseConductor variable tracks the state of this check box.

Blink highlighting
Accelerator: h
When this box is checked, the highlighting in physical windows will blink. When unset, the highlighting will use the static highlighting color. Associated highlighting in electrical windows will always blink.

With a path being displayed, pressing the h key will toggle the blinking status.

Enable sub-path selection
This check box enables sub-path selection while in the Select Path or "Quick" Path modes.

When a path is displayed, the user can click on two objects in the path, and only the ``sub-path'' connecting the two objects will be highlighted. If the two objects are connected in multiple ways, the algorithm will select one (which may not be the most direct). If Shift is held while clicking on an object in the path, the object will be deselected and not considered as part of the path. This can be used to coerce a desired sub-path. When a sub-path is displayed, clicking on any non-selected object will display the full path containing that object.

Load Antenna file
Accelerator: f
This button applies to the Select Path mode only. Pressing this button will load a previously-generated antenna report file (from the !antenna command) for the current cell, and ask the user for a net number found in the file. The conductor path corresponding that that net number will be highlighted.

Pressing the f key while in Select Paths mode will also query an antenna report file in a similar manner.

To trapezoids
Accelerator: t
Pressing this button will decompose the geometric objects which comprise the currently shown physical conductor path into trapezoids. This has no effect on ``real'' objects in the database or in the extraction system, only the temporary objects used to display the selected path.

This can be useful in conjunction with the sub-path selection capability, to enable breaking a path by deselecting parts of an object that are separate as trapezoids. It may also be useful as a prelude to the Save operations in some cases.

Pressing the t key with a path displayed will also convert the path to trapezoid representation.

Save path to file
Accelerator: s
If a physical conductor path is being displayed, this button enables saving the objects that comprise the path to a native cell file. Only the selected objects will be exported. If the path has been converted to trapezoids, the trapezoid representation will be exported. Pressing the button brings up a small pop-up where the user can give a cell/file name. The resulting file can be read into Xic at a later time for further processing, or for conversion to another file format.

By default, the via layers are not included in the file, only the conductors. The two check boxes below the button allow saving the vias and other associated layers as well.

Pressing the s key with a path displayed will also save the path to a file in a similar manner.

Path file contains vias
This check box applies when the Save path to file button is used. When checked, the via objects that connect layers will be included in the generated path. If not checked, only the metal layers that constitute the path will be included in the file. The via layers are those that have the Via keyword defined in the technology file. The file will included the objects on the via layers, clipped to the intersection area of the two associated conductors.

Path file contains via check layers
This check box applies when Save path to file is used, and the Path file contains vias check box is checked.

The Via keyword line in the technology file contains an optional layer expression, which must be ``true'' for an actual connection to be indicated. For example

Via SBST MET1 DIFF&PPLS

This line would indicate that the layer containing this line forms a via between conductors SBST and MET1 only in the presence of layers DIFF and PPLS.

When this check box is checked, the file will contain the layers needed for the checking expression (DIFF and PPLS), clipped to the via layer objects. If not checked, the file will contain only the vias that meet the check criteria, but the layers needed for checking (DIFF and PPLS) will not appear.

With this box checked, the file can be loaded into Xic and extraction run, and the (single) net will be completely identified. This may not be the case if check layers are missing, and certainly won't be the case if via layers are omitted.

The two via inclusion check boxes track the state of the PathFileVias variable. If this variable is set as a boolean (i.e., to no value), then vias will be included, and check layers will not be included. If the variable is set to any text, the check layers will also be included.