Introduction to SKILL

Cadence SKILL is a high-level, interactive programing language based on Lisp. There are various flavors of SKILLs available, depending on the tool. For example, Allegro SKILL is supported in Allegro PCB Editor, which is a PCB design tool, while Virtuoso SKILL caters specifically to IC (Integrated Circuit) design tasks. APIs for the tool are usually prefixed according to the tool name or feature name. Despite variations in their APIs, all flavors of SKILLs are built over a common core SKILL engine.

Because this post is about Allegro SKILL, we will mainly be talking about Allegro SKILL here.

Allegro SKILL APIs provide access to the database for Allegro PCB Editor and Advanced Package Designer+ (APD+). Allegro SKILL APIs have a prefix, axl, in their names, which stands for Allegro Extended Language. AXL functions are classified into families that typically have similar calling sequences and share a common part of their names, for example, the axlDBCreate family with members such as axlDBCreateShape and axlDBCreateSymbol.

You can use SKILL to write custom commands and extend the functionality of Allegro PCB Editor to meet your company’s specific needs.

How to run Allegro SKILL

Because SKILL is an interpretive language, no compiling is needed. There is no IDE for Allegro SKILL, but you can highlight the code in Notepad++ and Visual.

You can run AXL-SKILL by typing skill on the Allegro PCB Editor command line. The AXLSKILL interpreter appears with a skill> prompt in place of the Allegro PCB Editor command line.

You can also run AXL-SKILL functions from the Allegro PCB Editor command line with the following syntax:

skill <function-name> <arguments> 

Type exit to close the AXL-SKILL interpreter and return to the Allegro PCB Editor command line.

You can get a larger SKILL-only window by setting the Allegro PCB Editor environment variable, telskill. 

command > set telskill

Licenses required for Allegro SKILL

Allegro PCB/Packaging tools do not need a separate license to run SKILL or Allegro SKILL. By default, SKILL and Allegro SKILL come with all necessary licenses.

Types of Allegro SKILL APIs

Allegro SKILL has APIs for the following objects:  

• Allegro PCB Editor database objects: Reading database, creating objects, interactive Allegro PCB Editor commands like Delete Objects and Show Objects
• Allegro PCB Editor database parameter objects: Read/Write access.
• Using PCB Editor command window: Setting Allegro variables, running commands on the Allegro PCB Editor command window
• GUI or user interface functions: Creating new forms with fields like buttons, TreeView, tabs, and so on; predefined forms for prompting and getting confirmation from the user, displaying text files, ASCII files.
• Command control functions: Registering and unregistering SKILL commands with the command interpreter, getting and setting controls for the line lock, active layer, defining popups, getting user data.
• Constraint Management: Getting and setting current DRC modes and values for design constraints and ECSet members.
• Polygon operation functions: A polygon is a set of points linked such that the start and endpoint are same. A poly is always non-intersecting and may contain holes. A hole is a non-intersecting closed loop enclosed within a poly. You can perform geometric operations like Logical AND (the intersection of two polys) or query operations like the area or holes of the polygon.
• Utility functions, Math utility functions: Utility functions to access files and Math utility functions.

Refer to the Allegro SKILL User Guide to learn about these APIs in detail.

Allegro SKILL database

Allegro PCB Editor stores design data as various types of objects in a proprietary database format, which can create a complete representation of an electronic layout. You can create, operate on, and extract information from this database by using AXLSKILL APIs or functions.

Each Allegro database object has an associated type and a set of attributes that describe the object. The AXL-SKILL database stores both physical and logical information about the design.

• Physical information such as geometrical shapes (for example, connecting etch)
• Logical information such as nets and logical components

Accessing information from the database object

You can use the SKILL special attributes (? and ??) to see all attributes and all attribute/value pairs of an object. You can use an AXL-SKILL function with -> (the access operator) to access any object attribute. If the attribute does not exist for an object, the function returns nil.

Following is an example of using ->??

To flatten attributes in lists, use the ~> reference. For example, to get names of all nets in the design, you can do the following:

netNames = axlDBGetDesign()->nets~>name

Constraint Manager SKILL

Constraint Manager SKILL is a programable interface that provides access to the Constraint Manager data, including object information, relationships, and properties. Constraint Manager SKILL programs can be used in both Allegro PCB Editor and DE-HDL, offering flexibility and consistency across different design stages. Constraint manager SKILL API’s start with cm. APIs for Allegro PCB Editor start with cmxl.

To use Constraint Manager SKILL in Allegro tools, you need to use axlCMDBInit to initialize the Constraint Manager SKILL database.

There are many APIs in Allegro SKILL and DE-HDL SKILL to access the constraints such as axlCNSGetSpacing and axlCNSSetSpacing to get and set the Spacing Constraint Set. Following is an example to access actual values of the constraints like Relative Delay:

axlCMDBInit(); This function initializes the Constraint Manager database server.

dsn = cmxlFindObject(ACNS_DESIGN); This function queries the Constraint Manager database and returns an object if it exists.

ec1=cmxlFindObject(ACNS_ECSET, "Cadence", dsn); Cadence is the name of the ECSet.

cmxlDBSkillInit(dsn); This function initializes the Constraint Manager database for SKILL access.

cmxlGetPropertyNames(ACNS_ECSET, ACNS_NULL_ATTR_KIND ACNS_NULL_CATEGORY ACNS_ANY_ATTR_DOMAIN); This function is used to find the property name.

pc1 = cmxlGetAttribute(ec1 "TOPOLOGY_TEMPLATE_MAPPING_MODE"); This function queries an object for an attribute and returns the value as requested.

Feel free to comment if you want to know more about any other topic in SKILL!!