Performance Modeling and Analysis Using VHDL and System:Module Categories

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Module Categories

The ADEPT primitive modules may be divided into six categories: control modules, color modules, delay modules, fault modules, miscellaneous parts modules, and mixed-level modules.

As the name implies, the control modules are used to control the flow of tokens through the model. As such, the control modules form the major portion of the performance model. The control modules operate only on the STATUS field of a signal and do not alter the color of a token on a signal. Further, no elapsed simulation time results from the activation of the control modules since they do not have any delay associated with them. There are several control modules whose names end in a numeral, such as “union2.” These modules are part of a family of modules that have the same function, but differ in the number of inputs or outputs that they possess. For example, there are eight “union” modules, “union2,” “union3,” “union4,” …, “union8.” With the exception of the Switch, Queue, and logical modules, the control modules have been adapted from those proposed by Dennis [40].

The control modules described above process colored tokens but do not alter the color fields of the tokens passing through them. Manipulation of the color field of a token is reserved to the color modules. These color modules permit various operations on the color fields such as allowing the user to read and write the color fields of the tokens. The color modules also permit the user to compare the color information carried by the tokens and to control the flow of the tokens based on the result of the comparisons. The use of these color modules enables high-level modeling of systems at different levels of detail. These modules permit the designer to add more detail or information to the model by placing and manipulating information placed on the color fields of tokens flowing through the model. The color fields of these tokens can be set and read by these modules to represent such things as destination or source node addresses, data length, data type (e.g., “digital” or “analog”), or any type of such information that the designer feels is important to the design.

The delay modules facilitate the description of data path delays at the conceptual or block level of a design. As an example, the Fixed Delay module, or the FD module, may be used in conjunction with the control modules to model the delay in the control structure of a design which is independent on the type or size of an operation being performed. In contrast, the Data Dependent Delay module may be used to model processes in which the time to complete a particular operation is dependent on the amount or type of data being processed. The input to the Data Dependent Delay module is contained on one of the color fields of the incoming token.

The fault modules are used to represent the presence of faults and errors in a system model. The modules allow the user to model fault injection, fault/error detection, and error correction processes. The miscellaneous parts category contains modules that perform “convenience” functions in ADEPT. Examples include the Collector, Terminator, and Monitor modules. The Collector module is used to write input activation times to a file, and the Terminator module is used to halt simulation after a specified number of events have occurred. The Monitor module is a data-collection device that can be connected across other modules to gather statistical information during a VHDL simulation.

The mixed-level modules support mixed-level modeling in the ADEPT environment by defining the inter- faces around the interpreted and uninterpreted components in a system model. The functions of these modules and their use in creating mixed-level models is described in more detail in Sections 77.4.2 and 77.4.3.

The complete functionality of each primitive module is defined and the generics associated with each of the modules is described in the ADEPT Library Reference Manual [42]. The standard ADEPT module symbol convention is also explained in more detail in the ADEPT Library Reference Manual.

In addition to the primitive modules, there are libraries of more complex modules included in ADEPT. In general, these libraries contain modules for modeling systems in a specific applications area. These libraries are also discussed in more detail in the ADEPT Library Reference Manual.

ADEPT Tools

The ADEPT system is currently available on Sun platforms using Mentor Graphics’ Design Architect as the front end schematic capture system, or on Windows PCs using OrCAD’s Capture as the front end schematic capture system. The overall architecture of the ADEPT system is shown in Figure 77.11.

The schematic front end is used to graphically construct the system model from a library of ADEPT module symbols. Once the schematic of the model has been constructed, the schematic capture system’s netlist generation capability is used to generate an electronic design interchange format (EDIF) 2.0.0 netlist of the model. Once the EDIF netlist of the model is generated, the ADEPT software is used to translate the model into a structural VHDL description consisting of interconnections of ADEPT mod- ules. The user can then simulate the structural VHDL that is generated using the compiled VHDL behavioral descriptions of the ADEPT modules to obtain performance and dependability measures.

In addition to VHDL simulation, a path exists that allows the CPN description of the system model to be constructed from the CPN descriptions of the ADEPT modules. This CPN description can then be translated into a Markov model using well-known techniques and then solved using commercial tools to obtain reliability, availability, and safety information.

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