Design for Diagnosability
The New Courtship of CAD to a “Bigger World” Responsibility
The diagnostic engineer should discover that Advanced Testability and Diagnostic Modeling Software Tools (e.g. DSI International’s eXpress) will provide a “macro-framework” of diagnostic engineering capabilities that can be plugged into the design development processes – whether the design is new, evolving or legacy. However, the focus of this brief discussion is to examine a segment of the diagnostic engineering process that shall only concern itself with the process of exporting of CAD designs aCnd transferring these designs into the Design for Testability systems integration process using eXpress.
Once plugged into a robust Design for Testability process, the diagnostic engineer may discover a desire to reuse the design information from CAD as a well-fit opportunity to enrich their diagnostic engineering processes. At this time, the diagnostic engineer shall becomes initially acquainted with the current diagnostic interoperability limitations imposed by the typical CAD design environment. The CAD design environment is better suited to facilitate the typical low-level Design For Test (DFT) activities as adopted by the manufacturer and may be implemented in a practice that is unique to the individuality of any design engineer and the current design policies of the manufacturer. This discovery will be the initial enlightening where the diagnostic engineer and the design engineer shall become introduced to a hard “gap” in their diagnostic design process – that is, assuming that the manufacturer is either compelled or open to the enrichment of a diagnostic engineering process for diagnostic design engineering and influence purposes. This is also where the diagnostic engineer can begin to imagine the dividends of the synergies associated with bringing CAD design information into eXpress.
Given that we are only concerning this discussion with the transferring of design data from CAD tools and importing this data into eXpress, our scope of useful diagnostic data shall be further reduced to consist of the subset of diagnostic relevant data within the CAD. This subset may be further reduced by that data which can be represented in any forms (e.g. XML, Excel) by the Diagnostic Engineering tool and within the design input requirements as levied upon the CAD design engineer (in accordance with the designers typical role in his CAD designing process). Essentially, the range of data available for importing purposes may range from purely names of objects (BOM) and nets to also include some design dependencies and interrelationship data.
Currently, all CAD tools currently lack the vision or facilities to require enough design information for them to be of a perfect fit for diagnostic engineering. So, often we are left with the reusing of whatever bits of data we find to be useful and available from the CAD. Even then, the diagnostic engineer will still need to work inside the diagnostic engineering tool to augment the captured data. In eXpress, such tasks that are typically performed are the creation of tests, gather and map failure rate data to components, map internal component dependencies (outputs to inputs – particularly with unique FPGA’s) and map (functionally) to the designs at the next level up (electronic or non-electronic or mixed). Regardless of CAD tool capabilities, the diagnostic design should always take the leading role in the delegating and synthesizing of the design data as this method allows for the integrated mapping of the diagnostic capabilities to the requirements of the end product or integrated system.
In an ideal world, the CAD tool can be expected to provide a diagnostic engineer with a course and general topological representation of the schematic as an eXpress model, thus this representation (model) would be traceable to the electronic design within the CAD. However, it is much more typical that the CAD tool merely offers limited added value to the diagnostic process other than an evaluation point for the diagnostic engineering to assess the effort required to have the proper diagnostic engineering information “feedback” to the design engineer (working with the CAD). This assessment considers the institution of a collaborative environment between the CAD designer and the diagnostic engineer to assess evolving and iterative CAD designs and their respective diagnostic capabilities in the maturation of the integrated systems’ design. In this manner, the design has the opportunity to benefit from the assessments of the design’s diagnostics capabilities in the broader diagnostic terms of the larger (end product) system design as can be gleaned at any time using eXpress in the diagnostic engineering process.
In essence, the importing from a design in CAD is normally a “bottom-up” approach – making the next level up fit to the structure of the lowest level design. With eXpress, we want all of our customers to be fully capable to consider the requirements of the end product and force those requirements down to these lower level designs – a “top-down” approach. With eXpress you can map the requirements from the top level (or system level) to the lower design levels (through hierarchy in eXpress) and allow the diagnostics to meet in the middle. This is a course description of a “Diagnostic Engineering Process” as opposed to just allowing the bottom level CAD designs to limit the entire diagnostic capability of system by not being engaged in a diagnostic engineering process that maps these CAD designs to the end product or System and visa-versa.
In summary, Diagnostic Engineer needs to influence the design in CAD as a critical element of the design influence and the Design for Testability activity regardless. Making sure the designs in CAD are not used as a “fixed” method to trap and reduce the Diagnostic Capability of the end product or system is the paramount to the Design for Testability and Design for Diagnosability Process. If the CAD environment continues to limit the effectiveness of using a Diagnostic Engineering tool such as eXpress, it may not be of value to pull from CAD and instead use the inherent facilities in the Diagnostic Engineering tool in a successful collaborative and bi-directional diagnostic engineering process.