Patent Abstract:
Methods, software, and systems implementing software provide for accepting a user&#39;s selection of a database object defining layout being displayed. The database objects can include objects defining paths and path segments. Automatic layout tools may be used in creating at least some of the objects. The user&#39;s selection begins a recursive process of automatically selecting additional database objects based on criteria designed to create an uninterrupted spine from database objects on a single interconnect layer, of the same width, and collectively arranged such that the spine has a first end and a second end, and can be traced from the first end to the second end without backtracking.

Full Description:
FIELD 
     Aspects of the invention relate to tools for user editing and creation of layout for integrated circuits, and more specifically to ways to provide an aid to a user in editing of multiple logically related but physically independent database objects. 
     BACKGROUND 
     Layout tools use databases for storing objects defining portions of layout for an integrated circuit, such as portions of layout for a plurality of nets in the integrated circuit. For example, one database which can be used by design tools, such as Cadence&#39;s Virtuoso tool, is OpenAccess. The objects stored in an OpenAccess database can comprise a path object, and a path segment object, and other types of objects. 
     A path object is defined by a list of points defining multiple consecutive but not necessarily co-linear portions of interconnect, all formed on a single layer and of the same width.  FIG. 1  illustrates a portion of layout for an example path object  101  composed of a plurality of portions  102 ,  103  and  104 . The portions are created between points  105 ,  106 ,  107 , and  108  that would be stored in a data structure representing a computer readable representation of path object  101 . Path object  101  can be created by a designer who may specify each point and also specify a width for the path that is to connect each of those points. 
       FIG. 2  illustrates physical layout for path object  101  having width W. A user, when editing such a path object with a layout editor and selecting any point within a display of layout for path object  101  would cause selection of path object  101  in its entirety. 
     As evident from  FIGS. 1 and 2 , a path object is a single width, single layer portion of interconnect that may contain turns, and so would be defined by a beginning, an end, and zero or more intermediate points defining turns for that path object. 
     By contrast, a path segment object is defined as a single width, single layer linear strip of interconnect having a beginning and an end (i.e., there are no turns in a path segment object). Each such path segment is a separate layout database object that itself does not contain information about a higher-level construct of which it may be a part. In other words, even though a series of these path segments may be used by a tool to create an electrical connection between two circuit nodes, each path segment database object has no information about other path segments used in forming that connection. So, in a layout design tool, without any assistance to a designer, selecting layout corresponding to a given path segment generally would cause selection only of that single path segment object. Path segments objects are often preferred by automatic routing tools. 
     This concept of using path segments is further illustrated with respect to  FIGS. 3   a  through  3   d . In particular, the path object  101  of  FIGS. 1 and 2  is shown repeated as  FIG. 3   a , with arrows identifying portions of path object  101  that may be implemented as path segment objects  305 ,  310 , and  315  (i.e., 3 separate database objects) by an automatic layout tool for connecting points  108  and  105  ( FIG. 1 ). Each path segment object is specified by a start point and an end point. For example, object  305  is defined by points  108  and  301 , while object  310  is defined by points  311  and  106 . The points  301  and  311  would generally be defined using the same physical (x,y) coordinate (i.e., the same physical point in two-dimensional space), because the end point of one path segment object also is the start for the next path segment object. However, to emphasize that segment  305  and segment  310  are separate database objects, these points are separately numbered, being distinct stored values for each database object. 
     One implication of having logically separate path segments composing a single path of layout is illustrated in  FIG. 5 . Here, a cursor position is illustrated by number  510 . If a user selected the point on a screen illustrated by a cursor position  510 , then a layout tool would select path segment object  315 , even though the user may preferably have wanted to select the entirety of the physical interconnect (i.e., the layout defined by path segment objects  305 ,  310 , and  315 ) connecting points  108  and  105 . Instead, a remainder of such path segment objects ( 310  and  305 ) illustrated in outline and collectively numbered  505  would remain unselected. 
     One accommodation in this regard is illustrated in  FIG. 4 . Here, cursor click  410  is illustrated also as being in a position to select path segment object  315 . However, a mode can be provided that will allow selection of all electrically connected database objects (i.e., a net). For a simple configuration of interconnect elements, such as that illustrated in  FIG. 4 , this may be the desired behavior of the tools. However, more complicated situations exist where a designer may not desire to have selected all electrically connected path segment objects simply because the designer had clicked on one such path segment object. 
     SUMMARY 
     Aspects relate to providing a capability for a user to have assistance from a layout editor in selecting layout objects according to the examples, aspects, and other criteria presented. These aspects can be embodied in systems, methods, and computer readable media and can be used in editing and producing layout to be included in a fabricated integrated circuit. 
     Method aspects may include displaying a depiction of layout for an integrated circuit, the layout defined by database objects. Each database object being a respective single-width portion of layout, and formed on any one of multiple interconnect layers, and having respective first and second ends. Generally, a start and an end for each database object is defined as a separate point stored in a database, e.g., an (X,Y) coordinate. For an object having turns, each turn also can be defined by a point stored in the database for such object. For example, points  105  and  108  define start and end points for path object  101  (labeling either point as a start or as an end is arbitrary in this example). 
     The method includes accepting a user selection of one of the database objects as a start of a spine definition, and setting the first end of the selected object as a current end of a current object. The method also comprises determining, whether the current end of the current object corresponds to a first end of a single additional database object, of the same width, on the same layer, and of the same net as the current object, and if so then the method comprises adding the additional object to the spine definition, and repeating the determining with the second end of the additional database object as the current end of the current object. 
     The method also comprises determining whether the current end of the current object corresponds to first ends of two or more additional database objects, and if so then determining whether exactly one of the two or more additional database objects is of the same width, on the same layer, and of the same net as the current object, and if so then adding that one additional database object to the spine definition and repeating the original determining with that one additional database object as the current object. 
     If not then the method comprises determining whether exactly one of the two or more additional database objects has a first end segment collinear with a segment of the current end of the current object, and if so then adding that additional database object to the spine definition and repeating the original determining with that one additional database object as the current object. 
     If not then the method comprises terminating an end of the spine definition corresponding to the current end of the current object, and repeating the original determining step with the second end of the selected object as the current end of the current object; and outputting an indication of database objects comprising the spine definition. 
     Other aspects can include implementations that first use co-linearity of an end to a spine being defined with potential objects that may be added to the spine. For example, a method (can be implemented by computer instructions stored on suitable media) can comprise accepting a selection of a layout object defining a portion of layout for a net, and adding the selected object to a spine definition. A current object can be identified as the selected object, and a first end of the selected object as a current end. The spine definition can be supplemented by adding to the spine definition any other layout object having a first end collinear with and corresponding to the current end of the current object, and of the same width, on the same layer and the same net. The other layout object can then be the current object, and a second end of the other layout object can be the current end of the current object, and the adding above can be repeated for further layout objects meeting the criteria set forth. Upon not adding an object to the spine definition based on the above repetition, the spine can then be added to by adding to the spine definition any single non-collinear object having a first end corresponding to the current end of the current object, and of the same width, on the same layer, and of the same net as the current object, setting the non-collinear object as the current object and a second end of the non-collinear object as the current end. The spine analysis can then be repeated from the co-linear analysis above. The method also comprises terminating an end of the spine corresponding to the current object if no object was added in the above steps. If both ends of the spine are not yet terminated, then the above analysis can be repeated for a non-terminated end of the spine (the selected object). 
     In these aspects, what may be termed as two determinations or decisions, such as determining whether a single or multiple layout objects start/end at a given point (or correspond to a given other layout object), can be implemented as a single determination. Other such considerations also can be envisioned based on the examples and other aspects described. 
    
    
     
       BRIEF SUMMARY OF THE FIGURES 
         FIGS. 1 ,  2 ,  3   a - d ,  4  and  5  illustrate background aspects of integrated circuits, including the automatic construction of path segment objects by layout tools; 
         FIG. 6  illustrates one electrically connected net formed on multiple layers and having a plurality of portions that are of differing widths, and that such a net can be displayed on a computer display for editing; 
         FIG. 7  illustrates an example construction of the net of  FIG. 6  with path segments; 
         FIGS. 8   a - 8   e  illustrate a build of a spine according to examples and aspects herein; 
         FIGS. 9   a - 9   c  illustrate a build of a second spine according to examples and aspects presented herein; 
         FIG. 10  illustrates steps of a method that can be implemented to result in the spines constructed in the examples of  FIGS. 8   a - 8   e  and  FIGS. 9   a - 9   c ; and 
         FIG. 11  illustrates a computer system in which such methods can be implemented. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 6  is used for illustrating layout for a net  600  (an electrically connected plurality of pieces of physical layout) formed from layout defined by numerous database objects, and a designer may desire to select a portion of those database objects (i.e., layout defined by those objects). Often, layout defined by each of the different database objects can be formed on different interconnect layers, and thus can be connected by vias to other layout of net  600 . 
     In  FIG. 6 , layout portion  623  is connected by via  605  to the remainder of the net  600 . Further with regard to  FIG. 6 , W indicates that those path segments all have the same width (W). Other layout portions that are part of net  600  includes layout portions  622 ,  621 , and  601 . 
       FIG. 7  illustrates an implementation of net  600 . In this example, and those that follow, a piece of layout is defined by data contained in a database object, so for ease of reference, layout defined by an object (e.g., a depiction of a physical realization of the layout on a display) is sometimes referred to as the database object itself (e.g., object  708  can refer to layout defined by object  708 ). Also, the term object is used generically to refer to path database objects, and path segment database objects (as described in the Background). A path database object is defined on a single interconnect layer by a start point, zero or more intervening points defining zero or more additional intermediate layout segments, and an end point, and a single width for the layout. A path segment database object is defined on a single interconnect layer by a start point, and end point, and a single width. 
     As can be discerned, objects of  FIG. 7  composing net  600  are shown as partially overlapping, to diagrammatically indicate that such overlapping objects share end points. The separate objects also indicate that at changes in direction of net  600 , a new layout database object can be used. For example, considering region  740  where net  600  includes a T intersection, that intersection is decomposed into objects  708 ,  709 , and  710 . Likewise, region  730  illustrates a T intersection formed by objects  707 ,  706  and  712 . Regions  730  and  740  illustrate intersections between objects formed on the same layer and having the same width. However, intersections can also be formed between objects having different widths, but yet are formed on the same interconnect layer. An example of this occurrence is the intersection between object  723  and object  711 . Also, intersections between objects formed on different layers can exist, for example, object  716  shares an end point with object  712  and would be electrically connected with a via as described with respect to  FIG. 6 . 
     As introduced with respect to  FIGS. 4 and 5 , a designer currently may be presented with an editing mode that would allow selection of all the objects electrically connected to form net  600 , or a designer presently may be permitted to select any one of the objects composing net  600  individually. However such modes or selection behaviors may not be helpful to a designer in a particular circumstance where a designer desires to select a portion of net  600  that would comprise a logically distinct portion of net  600 . 
     In these examples and aspects, one logically distinct portion of net  600  of interest is referred to as a “spine”, and can be defined according to examples and situations described herein. In some situations, an additional mode may be presented in a layout editor that would provide functionality to select a spine according to these examples. 
     Now turning to  FIG. 8   a , the description of how a spine may be extracted from net  600  is begun. In these examples, objects shown either are single segment path database objects or path database objects. As discussed above, path database objects can have multiple segments and the examples described here apply equally to such path database objects. Reference also is made to portions of method  1000  of  FIG. 10 . 
     Method  1000  can begin by depicting ( 1005 ) a portion of layout on a display. A user may select ( 1010 ) a spine selection mode from among a number of modes that control a system&#39;s interpretation of a user&#39;s actions. In method  1000 , if a spine select mode was not selected, then a user&#39;s actions may be interpreted differently than the spine selection mode behavior described below, as identified by another action performed ( 1011 ) in  FIG. 10 . 
     Referencing  FIG. 8   a , the object  707  is shown to be selected by, for example, mouse click  805  (or any other way to receive an indication of object selection) (method step  1015 ). This is considered to be a first object added to a list of objects composing spine  800  (e.g., a spine definition). As each database object defines layout having a first end and a second end, a first end of the selected object  707  is defined (step  1020 ) as a current end of a current object. In most implementations, it is preferred to define database objects using points defining coordinates for their respective starting position, ending position, and any intermediate turns (for objects that can have 1 or more turns, such as a path object). 
     Then, it is determined (step  1025 ) whether the current end of the current object (in one instance, object  707 ) corresponds to a first end of a single additional database object that is of the width, formed on the same layer, and part of the same electrical net as the current object  707  (step  1030 ). If there is such an object, then that object also is added (step  1035 ) to the spine definition. 
     In the example of object  707 , it can be determined that only object  708  meets object  707  at the assigned current end of current object  707  ( FIG. 8   b ). Also, it can be determined that object  708  has the same width as object  707  (i.e., layout defined by object  708  is same width as layout defined by object  707 ). Therefore, object  708  can be added to the spine definition ( FIG. 8   b ). 
     Then, in  FIG. 8   c , object  708  is assigned (step  1038 ) to be the current object and the far end of object  708  to be the current end of the current object. The method  1000  returns to step  1025 . Again at step  1025 , it is determined that object  708  meets objects  709  and  710  in region  740  ( FIG. 8   c ), so method  1000  proceeds to step  1040 , where it is determined that the current end meets multiple additional objects (of course, this step can also be combined with step  1025  in that a number of objects meeting at a given point can be once determined, but is split out for the sake of explanation.) Then it is determined (step  1050 ) whether exactly one of these objects is the same width, layer, and net as the current object. In this case, it is determined (steps  1050 / 1055 ) that more than one of objects  709  and  710  (illustrated in outline) meet these criteria, and it also is then determined (step  1060 ) that neither object  709  or object  710  is co-linear, so method  1000  proceeds to terminate (step  1070 ) the current end, and set (step  1075 ) the other end of the selected object as the current end of the current object, and return to step  1025 . 
     In  FIG. 8   d , and again at step  1025  with the other end of object  707 , method  1000  gets to step  1055  again, based on similar considerations as those described above (with objects  712  and  706  being two (multiple) objects defining layout of the same width, same layer, same net as object  707  and meeting object  707  at region  730 ). However, in this case, step  1060  finds that object  706  is collinear with object  707 , while object  712  is not (region  730 ). So, object  706  is added ( 1035 ) to the spine definition, object  706  is defined ( 1038 ) as the current object, and the far end of object  706  is defined as the current end. In  FIG. 8   e , method  1000  returns to step  1025 , where it is determined that object  706  meets only object  705 , and it is also determined ( 730 ) that object  705  is same width, layer, and net as object  706 , so object  706  is added ( 1035 ) to the spine definition. The current object now is object  706 , and its far end is the current end. 
     Still in  FIG. 8   e , method  1000  again returns to step  1025 , and then to step  1040 , as it is determined that there are neither single nor multiple additional objects corresponding to the current end of the current object; meaning that there are no additional objects. Therefore, the spine is terminated ( 1070 ), since both ends of the originally selected object have been explored until no further layout objects meeting the outlined criteria are identifiable. 
       FIGS. 9   a - 9   c  are used to show a contrasting result. Here, a designer is shown as selecting object  711  with selection  905 , and begins spine  900 . As shown in  FIG. 7 , object  711  intersects objects  723  and  710 . Referencing method  1000 , the decision process is through step  1025 , step  1040 , and step  1050 , where it can be determined that only object  710  is of the same width, layer, and net as object  711 , and can be added to the spine  900  (step  1035 .) 
     Object  723  is not added to spine  900 , as it is not of the same width as object  711 . A separate, independent, and alternative reason is that object  710  is co-linear with object  711 , while object  723  is not. 
     Now, in  FIG. 9   c , object  710  is the current object, and its end remote from object  711  is the current end. It is determined that the current object proceeds through steps  1025 ,  1040 ,  1050 , and  1055 , to determined that multiple same width, layer, and net objects meet the current object (objects  708  and  709 ). So, at step  1060 , it is determined that only object  709  is collinear, is added to spine  900 , and is now the current object. Since object  721  is not the same width as object  709 , it is not added to the spine, and that end of the spine terminates  1070 . Since selected object  711  has no objects corresponding to its other end (steps  1025 ,  1040 ), that end also will terminate  1070 . 
     Thus, it is apparent that a spine composed of a selection of layout objects defining a net, according to present aspects, can depend on what object was selected initially as an object that is to be part of the spine. For example, by selecting an object on a lateral portion of net  600 , a predominantly lateral spine can result, while selecting an object on a vertical portion of net  600  can result in a predominantly vertical spine (although outcomes may vary, depending on the nature of a given spine.) 
     In method  1000 , certain steps were separately identified for the sake of clarity and explanation. However, some steps may allow a conclusion as to the existence of other conditions, and so certain steps may not need to be separately executed. For example, the separately recited steps  1025 ,  1040 , and  1050 / 1055  may be combined into respectively single steps with multiple branches therefrom. Also, there is no requirement that the analysis of each end of the selected segment proceed sequentially, as they also can proceed in parallel. 
     Also, co-linearity can be used as a more primary decision criteria, in that a spine definition can be formed based first on a selected object, then adding any single other layout object having a first end collinear with and corresponding to the current end of the current object, and of the same width, on the same layer and the same net, and looping until no more objects were added on this basis. Since objects can have parts that are not co-linear with each other (i.e., path objects can have turns), a decision criterion can be whether the joining ends are co-linear, and not whether an entire object is co-linear with another. 
     Then, following on the far end of any added objects, the spine definition can then be extended by adding any single non-collinear object having a first end corresponding to the current end of the current object, and of the same width, on the same layer, and of the same net as the current object. In other words, if there is an object with a qualifying co-linear end, then whether that object is single or also with other objects non-colinear can be deemed irrelevant. When there is no collinear object, then only a single qualifying object should be present, or else the spine definition on that end should terminate (e.g., a T junction, coming from the bottom, should terminate). 
     In all cases, the term “width” can be considered within an approximation appropriate under the circumstances, and not to any particular degree of mathematical precision. 
       FIG. 11  illustrates a computer system  1100  in which methods according to the examples and aspects of the above description may be implemented. Computer system  1100  includes keyboard  1120 , mouse  1121  connected to a user interface  1115 , which in turn connects these user interface tools to a CPU/chipset  1105 . In some implementations, CPU/chipset  1105  may comprise a plurality of physically separate chips interconnected by means such as traces on a motherboard, or intrapackage connections, and the like. CPU/chipset  1105  may also comprise various caches and other supporting circuitry. CPU/chipset  1105  communicates with a memory  1125  in which it can store programs and other data for executing programs, as well as a non-volatile memory  1150  in which such programs and data can be stored when not more immediately needed or being used. For example, a layout database  1151  can store layout objects discussed herein. This database can be an OpenAccess database. Memory  1150  can store application code  1152 . In system  1100 , a display  1140  is driven by user interface  1115 , but in other examples, display  1140  can be driven by circuitry contained within CPU/chipset  1105 , or by a chip driven by CPU/chipset  1105 . 
     Methods and other implementations can be distributed among a plurality of computers connected in a network. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, the computer uses that connection as a computer-readable medium. Thus, by way of example, and not limitation, computer-readable media can also comprise a network or data links which can be used to carry or store desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. 
     Computer-executable instructions comprise, for example, instructions and data which cause or otherwise configure a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. The computer executable instructions may be, for example, binaries, intermediate format instructions such as assembly language, or source code. For example, systems, software, and methods can include providing a mode allowing activation of the functionality described herein. For example, a mode can be provided in a layout editor, such as Virtuoso, by Cadence Design Systems, Inc. implementing such functionality. 
     Although some subject matter may have been described in language specific to examples of structural features and/or method steps, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to these described features or acts. Rather, the described features and steps are disclosed as examples of components of systems and methods within the scope of the appended claims.

Technology Classification (CPC): 6