Design for manufacturability dfm and design for testability dft reporting are perhaps the best differentiators to identify a leading electronic contract manufacturer cm. Examples of good candidates for observation points. In this post, i want to argue for a design heuristic that ive found to be a useful guide to answering or influencing many of these questions. Now lets try another design change for the sake of testability. Dfm and dft reports detect and address issues before they cost you money on the production line. Tutorial on design for testability dft an asic design. Time to market new products microprocessor board testability subjects. Software testability is the degree to which a software artifact i. Design for testability needs to be considered during layout to prevent signal integrity problems and ensure a working scan chain.
Design for testability we just learned how the use of mocks and stubs can help developers in being highly productive and efficient in writing test code. Thats an example of the tradeoffs that can exist between testability and design. The circuit with poor testability causes big time andor cost losses during postfabrication testing and testing for serviceability. If you design a testability feature, you probably wont need to use it. Sep 27, 2019 dft means design for testability, where logic will be implemented or inserted in the core design at rtl stagenow a days most of the company prefer at rtl stage or netlist stage. Conflict between design engineers and test engineers. Test example sa1 sa0 a 3 a2 a 3 a 2 a y n1 n2 n3 a 1 a0 1 a 0 n1 n2 n3 y minimum set. Whenever you design an experiment, from the start, it must always revolve around this central tenet of testability. The design has changed, but maybe not for the better. Designfortestability needs to be considered during layout to prevent signal integrity problems and ensure a working scan chain. We have seen in previous chapters that conditions that are very complex e. The bigger the system, the harder it is to develop and maintain, and the harder it is to test.
This is a comprehensive tutorial on dft with emphasis on concepts of digital application specific integrated circuit asic testing incorporating boundary scan architecture in. Design for testability dft is just one aspect of the current clamor about a variety of initiatives aimed at speeding innovative, high quality, customerdriven new products to market in a timely, profitable manner. Mar 24, 2017 this feature is not available right now. For example, if this code is part of a smart house system we would expect it. A general recommendation to design for testability comes down to separating domain from infrastructure. Designing for testability production ready programming. For example, technologies that support the inversion of control may be useful, not only in terms of designing a flexible system, but also in relation to testability. Some of the flaws listed in the testability guide, by hevery flaw. In your example with typemock you achieve the same testability without making any design changes, whereas mine requires a few. Feb 10, 2019 this is an introduction to the concepts and terminology of automatic test pattern generation atpg and digital ic test. The checklists prepared during the last phase should be supplied to the designer.
Design and construction, integrated circuits, large scale integration, printed. Only need to verify around 100 states to get 99% fault coverage. A vital aspect of the system architect role in safe. Since dsi is the original pioneer of the need for testability as an integral component of the design development process for the us department of defense, and has mentored william keiner, author of the first testability standard milstd 2165 prior to its acceptance in 1981, we have continued to lead industry in this. Design for testability dft dft techniques are design efforts specifically employed to ensure that a device in testable. Test example sa1 sa0 a 3 0110 1110 a2 10101110 a 3 a 2 a y n1 n2 n3 a. The design should elucidate the system path clearly so that testing team knows which programs are being touched in what scenario. Whenever you create a hypothesis to prove a part of a theory, it must be testable and analyzable with current technology you may develop a great hypothesis to try to verify part of a theory but, if it involves a lot of resources and money that you do not have, it is effectively invalid. O good design practices learnt through experience are used as guidelines for adhoc dft. In this example, the stimulus sources that can impact testability are internal and external. The purpose of manufacturing tests is to validate that the product hardware contains no. The purpose of manufacturing tests is to validate that the product hardware contains no manufacturing defects that could adversely affect the products correct functioning. If you follow the steps of the scientific method and use all of the scientific elements, including initial conception, hypothesis generation and obtaining analyzable results, then you will have fulfilled the fundamental basics of testability.
The domain is where the core of the system lies, i. Many benefits ensue from designing a system or subsystem so that failures are easy to detect and locate. Moreover, when dealing with legacy systems, it can be. If the testability of the software artifact is high, then finding faults in the system if it has any by means of testing is easier. Testability in design build a number of test and debug features at design time this can include debugfriendly layout for wirebond parts, isolate important nodes near the top for facedownc4 parts, isolate important node diffusions this can also include special circuit modifications or additions. These guidelines should not be taken as a set of rules. Out 0 1 2n1 c mux to reduce the number of output pins for observing monitor points, multiplexer can be used. More frequently, the better solution is to create a new class, and move the behavior that was previouly private to the public side of the new class. Combined with everincreasing design complexity with multiple memories, mixed signal blocks and ips from multiple vendors crammed into a single soc, design for test dft implementation and production test signoff has become a major challenge. Throughout this book we have been using business systems as examples. These sources can generate events when hardware and software elements within the embedded system have been completed or updated, and are ready to be tested. However it is important to design the integrations for testability and this starts with the way you setup the proxies.
The testability is one of the most important requirements which should be considered along with other essential constraints such as performance or cost when designing a circuit. The cost of manufacturing the blank pcb, the cost of components, the assembly costs, and the cost of test. Ask how indepth the assessments go prior to production, and what the company will do if it encounters any issues, errors, or defects. What are the good books for design for testability in vlsi. Lecture 14 design for testability stanford university.
Designing for testability in pcb design the overall cost to produce a completed printed circuit board pcb can be broken down into several basic categories. A vital aspect of the system architect role in safe by alex yakyma the bigger the system, the harder it is to develop and maintain, and the harder it is to test. Dft is a general term applied to design methods that lead to more thorough and less costly testing. Design for testability techniques zebo peng, ida, lithzebo peng, ida, lith tdts01 14 tdts01 lecture notes lecture 9lecture notes lecture 9 design for testability dft to take into account the testing aspects during the design process so that more testable designs will be generated. This is an introduction to the concepts and terminology of automatic test pattern generation atpg and digital ic test. Implementation decisions for instance, having too much logic at db side a common problem of manymany products makes testing virtually impossible. Design for testing or design for testability dft consists of ic design techniques that add. Failure modes, effects and criticality analysis fmeca 7. In order to incorporate testability in this phase inputs and expected outputs should be clearly stated.
Enterprise reliability, availability, maintainability and. Design for testability in digital integrated circuits. Wso2 esb design for testability roger vd kimmenade. This is industry evident by the use of design for testing dft techniques. Design for testability dft has migration recently from gate level to registertransfer level rtl vlsi test principles and architectures ee141 ch. The approach to integrate gtest with the build environment cmake in this repository is not the best approach with relation to continuous integration, maintenance, etc. Ad hoc design for testability techniques multiplexing monitor points. I imagine the development of the saturn v rocket, space shuttle, automobiles, robotics, etc. Design for manufacturability design for testability. Controllability and observability controllabilitydeterminesthe work it takes to set up and run test cases and the extent to which individual functions and features of the system under test sut can be made to respond to test cases. Tutorial on design for testability dft an asic design philosophy for testability from chips to systems abstract.
The need to assess a products capabilities and behavior in a realworld setting is paramount. Interrelationships between reliability, availability, maintainability, and testability 2. Testability and testability analysis is an integral part of all design practices. Designing for testability the technology, the technique, and the economics thomas j. May 06, 2018 ask about design for manufacturabilitydesign for testability reporting before you decide while interviewing different cms, ask about the companys dfm, dft, and other reporting services. Block 1 block 2 block 1 is not observable, block 2 is not controllable block 1 1 block 2 cp1 improving controllability. Below we will cover some basic examples of the issues encountered when trying to write unit tests. This may seem like a case of design before requirements but the content of the detail specification does not apply to the design of the product, rather the design of the acceptance test process. This voluminous book has a lot of details and caters to newbies and professionals. In this video, we will go over the following concepts. The authors wish to express their thanks to comett.
Tests are applied at several steps in the hardware manufacturing flow and, for certain p. Logic verification accounts for 50% of design effort for many chips. So i thought wed walk through an example to see how making code testable which doesnt necessarily mean testing it can turn some bad code into. First, we calculate the combinational and sequential controllability measures of all signals. The added features make it easier to develop and apply manufacturing tests to the designed hardware. Other guidelines, for example, deal with the electromechanical characteristics of the interface between the product under test and the test equipment. Aug 19, 2010 despite my previous attempt you may still not believe that testability has a lot less to do with testing and a lot more to do with good design. In our previous chapter, it was easy to pass an issuedinvoices stub to the invoicefilter class.
Design for testability in digital integrated circuits bob strunz, colin flanagan, tim hall university of limerick, ireland this course was developed with part funding from the eu under the comett program. Build a number of test and debug features at design time this can include debugfriendly layout. This test circuit verifies that core design does not have manufacturing defects focusing on circuit structure rather than functional behavior. The following guidelines provide suggestions for improving the testability of circuits using xjtag. So i thought wed walk through an example to see how making code testable which doesnt necessarily mean testing it can turn some bad code into something beautiful. This blog gives some guidelines which you can use to design for testability. Despite my previous attempt you may still not believe that testability has a lot less to do with testing and a lot more to do with good design. So, this is still a case of requirements before design. To reduce the number of inputs, a counter or a shift register can be used to drive the address lines of the multiplexer disadvantage.
Design for testability design for testability dft dft techniques are design efforts specifically employed to ensure that a device in testable. Calculation of standard metrics for defenseaerospace. Optimize your code for testability specifically, this means that when you write new code, as you design it and design its relationships with the rest of the system, ask yourself this question. This is a comprehensive tutorial on dft with emphasis on concepts of digital application specific integrated circuit asic testing incorporating boundary scan architecture in asic design. For wirebond parts, isolate important nodes near the top for facedownc4 parts, isolate important node diffusions. Testability how to create a scientific theory or hypothesis. The circuit with poor testability causes big time andor cost losses during postfabrication testing and testing for. General tck needs to be as free as possible of glitches and spikes, since all operations are triggered by rising and falling tck edges. Dft means design for testability, where logic will be implemented or inserted in the core design at rtl stagenow a days most of the company prefer at rtl stage or netlist stage. Awta 2 jan 2001 focused on software design for testability.
In many cases the house logic can be complex and can depend on other parts of the system. Design for testability 5cmos vlsi designcmos vlsi design 4th ed. Physical world examples of design for testability and test. Aug 31, 2016 o is a strategy to enhance the design testability without making much change to design style. The potential advantages in terms of testability should be considered together with all other implications which they may have e. This can also include special circuit modifications or additions.
Design for testability jacob abraham, november 7, 2019 1 38. Testability is one of the underestimated qualities of software. Lecture 14 design for testability testing basics stanford university. Silicon debug test the first chips back from fabrication if you are lucky, they work the first time if not logic bugs vs. Systems that cant be changed cant be developed and delivered in an agile manner. Design for testing or design for testability consists of ic design techniques that add testability features to a hardware product design. Design for testability jacob abraham department of electrical and computer engineering the university of texas at austin vlsi design fall 2019 november 7, 2019 ece department, university of texas at austin lecture 20. Ad hoc design for testability techniques method of test points. Systems that cant readily be tested cant readily be changed. Continuously shrinking process nodes have introduced new and complex onchip variation effects creating new yield challenges. Design for testing or design for testability dft consists of ic design techniques that add testability features to a hardware product design.
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