Design for testability example

This is industry evident by the use of design for testing dft techniques. Interrelationships between reliability, availability, maintainability, and testability 2. Designing for testability production ready programming. Design for testing or design for testability dft consists of ic design techniques that add testability features to a hardware product design. The bigger the system, the harder it is to develop and maintain, and the harder it is to test. The following guidelines provide suggestions for improving the testability of circuits using xjtag. 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.

Some of the flaws listed in the testability guide, by hevery flaw. 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 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. Testability is one of the underestimated qualities of software. This voluminous book has a lot of details and caters to newbies and professionals. This is a comprehensive tutorial on dft with emphasis on concepts of digital application specific integrated circuit asic testing incorporating boundary scan architecture in. In many cases the house logic can be complex and can depend on other parts of the system. Only need to verify around 100 states to get 99% fault coverage. Design for manufacturability dfm and design for testability dft reporting are perhaps the best differentiators to identify a leading electronic contract manufacturer cm. 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. Lecture 14 design for testability testing basics stanford university. Design for testing or design for testability consists of ic design techniques that add testability features to a hardware product design. In this video, we will go over the following concepts.

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. 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. Tutorial on design for testability dft an asic design. Calculation of standard metrics for defenseaerospace. Lecture 14 design for testability 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. 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. 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. Designing for testability the technology, the technique, and the economics thomas j.

The purpose of manufacturing tests is to validate that the product hardware contains no. 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. Testability and testability analysis is an integral part of all design practices. The circuit with poor testability causes big time andor cost losses during postfabrication testing and testing for serviceability. Implementation decisions for instance, having too much logic at db side a common problem of manymany products makes testing virtually impossible. Apr 04, 2007 but i feel that testability is an important attribute of quality code, right along side scalability, extendability, readability, etc. Design for testability 5cmos vlsi designcmos vlsi design 4th ed.

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. Conflict between design engineers and test engineers. Design for testing or design for testability dft consists of ic design techniques that add. 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. Ask how indepth the assessments go prior to production, and what the company will do if it encounters any issues, errors, or defects. Design for manufacturability design for testability reporting. 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. Thats an example of the tradeoffs that can exist between testability and design. Aug 31, 2016 o is a strategy to enhance the design testability without making much change to design style. 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. Out 0 1 2n1 c mux to reduce the number of output pins for observing monitor points, multiplexer can be used. Design for testability dft has migration recently from gate level to registertransfer level rtl vlsi test principles and architectures ee141 ch. So, this is still a case of requirements before design.

Time to market new products microprocessor board testability subjects. 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. The potential advantages in terms of testability should be considered together with all other implications which they may have e. Design for testability needs to be considered during layout to prevent signal integrity problems and ensure a working scan chain. For wirebond parts, isolate important nodes near the top for facedownc4 parts, isolate important node diffusions. Essentials of electronic testing for digital, memory and mixedsignal vlsi circuits, by m. This can also include special circuit modifications or additions. Examples of good candidates for observation points. First, we calculate the combinational and sequential controllability measures of all signals. Design for testability design for testability dft dft techniques are design efforts specifically employed to ensure that a device in testable. Tests are applied at several steps in the hardware manufacturing flow and, for certain p. Feb 10, 2019 this is an introduction to the concepts and terminology of automatic test pattern generation atpg and digital ic test.

The domain is where the core of the system lies, i. 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. In your example with typemock you achieve the same testability without making any design changes, whereas mine requires a few. Moreover, when dealing with legacy systems, it can be.

We have seen in previous chapters that conditions that are very complex e. 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. If you design a testability feature, you probably wont need to use it. 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. Dft is a general term applied to design methods that lead to more thorough and less costly testing. Design and construction, integrated circuits, large scale integration, printed.

Ad hoc design for testability techniques method of test points. Enterprise reliability, availability, maintainability and. For example, if this code is part of a smart house system we would expect it. O good design practices learnt through experience are used as guidelines for adhoc dft. Systems that cant be changed cant be developed and delivered in an agile manner. 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.

In this example, the stimulus sources that can impact testability are internal and external. Awta 2 jan 2001 focused on software design for testability. 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. In order to incorporate testability in this phase inputs and expected outputs should be clearly stated. 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. 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. Logic verification accounts for 50% of design effort for many chips. What are the good books for design for testability in vlsi. Design for testability dft dft techniques are design efforts specifically employed to ensure that a device in testable. Systems that cant readily be tested cant readily be changed. Ad hoc design for testability techniques multiplexing monitor points.

This is an introduction to the concepts and terminology of automatic test pattern generation atpg and digital ic test. The purpose of manufacturing tests is to validate that the product hardware contains no manufacturing defects that could adversely affect the products correct functioning. Now lets try another design change for the sake of testability. General tck needs to be as free as possible of glitches and spikes, since all operations are triggered by rising and falling tck edges. These guidelines should not be taken as a set of rules. Build a number of test and debug features at design time this can include debugfriendly layout. Physical world examples of design for testability and test. Dfm and dft reports detect and address issues before they cost you money on the production line.

Mar 24, 2017 this feature is not available right now. 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. Other guidelines, for example, deal with the electromechanical characteristics of the interface between the product under test and the test equipment. Throughout this book we have been using business systems as examples. The need to assess a products capabilities and behavior in a realworld setting is paramount. However it is important to design the integrations for testability and this starts with the way you setup the proxies. The circuit with poor testability causes big time andor cost losses during postfabrication testing and testing for. 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. The checklists prepared during the last phase should be supplied to the designer. 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. In our previous chapter, it was easy to pass an issuedinvoices stub to the invoicefilter class. Test example sa1 sa0 a 3 0110 1110 a2 10101110 a 3 a 2 a y n1 n2 n3 a. Continuously shrinking process nodes have introduced new and complex onchip variation effects creating new yield challenges. Design for testability jacob abraham, november 7, 2019 1 38. Software testability is the degree to which a software artifact i. A general recommendation to design for testability comes down to separating domain from infrastructure. Wso2 esb design for testability roger vd kimmenade. To reduce the number of inputs, a counter or a shift register can be used to drive the address lines of the multiplexer disadvantage. The authors wish to express their thanks to comett. I imagine the development of the saturn v rocket, space shuttle, automobiles, robotics, etc.

A vital aspect of the system architect role in safe. Designfortestability needs to be considered during layout to prevent signal integrity problems and ensure a working scan chain. This test circuit verifies that core design does not have manufacturing defects focusing on circuit structure rather than functional behavior. 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. The added features make it easier to develop and apply manufacturing tests to the designed hardware. 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.

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. Design for manufacturability design for testability. This blog gives some guidelines which you can use to design for testability. 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. Below we will cover some basic examples of the issues encountered when trying to write unit tests. 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.

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. The design should elucidate the system path clearly so that testing team knows which programs are being touched in what scenario. The cost of manufacturing the blank pcb, the cost of components, the assembly costs, and the cost of test. Failure modes, effects and criticality analysis fmeca 7. Many benefits ensue from designing a system or subsystem so that failures are easy to detect and locate. 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.