Identifying testable and supportable commercial-off-the-shelf (COTS) equipment

In acquiring commercial-off-the-shelf (COTS) circuits - circuit boards, shop replaceable assemblies (SRAs), modules, and line replaceable units (LRUs) - the test and support engineers may concede that they are powerless to make COTS systems testable. This paper challenges that conclusion by asserting the acquisition power of the system designer to select COTS equipment that meets certain testability and supportability requirements. Criteria are introduced to evaluate the testability of COTS in order to understand the impact on supportability costs and future product improvements. Five testability attributes - Status, Transmit, Receive, Integrity of signal, and Diagnosability or STRID - are used as metrics. In a system setting COTS usually interfaces with other modules through standard buses, which themselves should undergo STRID evaluation. This is necessary, not only because system designers can choose the most testable bus, but also because the cause of the testability concern can be due to either the bus or the COTS unit. The paper outlines some standard buses, and details the testability analysis of the universal serial bus USB 3.0. Next, an example COTS, a video transceiver with USB interface is used to demonstrate STRID testability analysis of a COTS module. These results are compared to STRID metrics for other video transceiver choices. This type of analysis not only allows buyers to select more testable and supportable COTS, but we hope and believe that the same criteria will cause COTS designers for competitive reasons to create more testable COTS.