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Krishnendu Chakrabarty Durham, 28.01.2014
William H. Younger Distinguished Professor of Engineering
Executive Director of Graduate Studies
Department of Electrical and Computer Engineering Professor of Computer Science
Duke University
Durham, North Carolina, USA
Review
of the doctoral thesis prepared for
the Faculty of Electronics and Telecommunications of Poznan University of Technology
Title: Test compression bandwidth management in system-on-chip designs Author: Jakub Janicki
1. What are the research problems tackled in the thesis? Are they formulated clearly? What is the nature of the thesis (theoretical, experimental, other)?
This thesis addresses an important test-infrastructure design and optimization problem for core- based system-on-chip designs. The testing of “monster” SoCs has long been regarded as a major challenge and a key contributor to manufacturing cost in the semiconductor industry. There are several problems that must be tacked to manage test cost and ensure high product quality⎯these include, among others, test pattern generation for screening defects, test-data management, and test-delivery solutions. This PhD thesis includes a careful study of the last two problems, i.e., how to reduce the test-data burden for monster chips, and how to create a design-for-testability infrastructure that reduces test time and provides easy test access to embedded cores.
The thesis was a pleasure to read due to its clarity and rigor. The problem formulations are precise, clear, and complete. For an expert in the field, the thesis stands up nicely to critical scrutiny, while for the non-expert (i.e., someone qualified in a more general sense but not a domain-specific expert), the thesis articulates important problems, solution techniques, and results obtained in a clear and convincing manner.
The thesis is not overly theoretical but it does include formal statements of problems, as well as precise descriptions of algorithms. The thesis is strong in experimental content, with a lot of results for large industrial circuits. These results are certainly going to convince even then the most skeptical reader about the efficacy of the proposed solutions. Experimental work in the context of research in this domain does not imply bench-top work in the laboratory, or measurements with test chips and instruments. Instead, experimental work in this domain refers to extensive software development, implementation of optimization algorithms, and simulations using data for real-life industrial circuit designs.
2. Is the literature review comprehensive and up to date, and does it show understanding of the theoretical context (including the state-of-the-art solutions and relevant industrial applications)? Have conclusions drawn from this study been formulated in a clear and convincing way?
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The literature review is very comprehensive. To the best of my knowledge, citations have been provided to all work published in journals and conferences in the field over the past few decades.
A majority of these papers have also been discussed in the thesis in terms of their benefits and drawbacks. There is relatively less coverage of solutions that have been adopted by industry, but that is only expected for a university PhD thesis. The conclusions from the study are presented clearly in the form of graphs and tables. The claims are nicely supported by the data and the exposition is both lucid and convincing.
3. Has the author solved the tackled problems by using an appropriate (adequate) approach?
Have reasonable assumptions been made?
The scientific approach is rigorous and based on the recognized concepts from linear systems, heuristic algorithms, and optimization. The simulation methodology is sound. I am especially impressed that the simulations were not carried out using “toy” academic benchmarks but with actual industry designs. The assumptions made with respect to test access and tester technology are consistent with the state-of-the-art.
4. What is a new and original contribution of the thesis? How would you position the thesis with respect to the state-of-the-art solutions?
I consider this thesis to make two key contributions (with multiple sub-contributions within each):
• Test compression and output compaction solutions that are aware of tester channel realities.
These solutions can be adapted to make maximum utilization of the available tester channels to reduce test time.
• An SOC-level optimization (test scheduling and test-access architecture) solution that provide just the right size “data pipe” for delivery of test patterns to cores and test responses to the tester. Such a sizing solution reduces test time for the SOC and allows the best possible test resource utilization.
Test compression and SOC testing is a hot research topic and there are many ongoing research activities worldwide in this area. Despite such immense competition from other approaches, I would rate the novelty of this thesis as being very high. In particular, the matching of the EDT- based test compression solution to the availability of tester channels and the concept of test data circulation are novel. The bandwidth management and SOC-level optimization work improves upon some of my own past work.
The novelty and impact of this thesis can be gauged from the very impressive publication list- papers that have resulted from this work. Three papers have been published in the top conference (ITC) and two papers have been published in the top journal (TCAD) in the field.
5. Has the author shown abilities to present the achieved results in a correct and convincing manner (conciseness, clarity, editorial correctness)?
I rate the thesis very highly for clarity, editorial quality, and conciseness. In some places, I feel that it is a little too concise or terse, a criticism that I describe in more detail in the next section.
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6. What are weak points of the thesis and its main drawbacks?
The few weaknesses of the thesis are of a minor nature. I list these weaknesses below:
• The thesis can benefit from carefully chosen examples and test cases that can motivate the problems and illustrate the proposed solutions.
• A number of algorithms and optimization techniques have been developed as part of this research. However, the thesis does not provide sufficient details about these algorithms for a reader or researcher who would like to implement them. It is recommended that descriptions in pseudo-code form or flowcharts be added to the chapters, or at last to an appendix. These algorithms should also be illustrated with examples in appropriate places.
• Some theoretical results on fundamental limits (e.g., of the output compaction method) will provide even more rigor to this thesis.
• I have a quibble about the use of the term “bandwidth”. In my view, bandwidth is the product of bitwidth and clock frequency (or data transfer rate). Since the clock frequency is not being modulated in this thesis, I feel that the appropriate term should be bitwidth. Of course I realize that bandwith has been used in published papers so it will be difficult to make the change only for the thesis.
• Some discussion can be added on how the bandwidth management scheme can be utilized (or simplified?) for a mainly homogenous SOC with many identical cores. Most SOCs today are of this category. Also, there can be some mention of how fault diagnosis can be done by tracking the multiple (optimized) data streams.
• Finally, I noticed at least one place where there a claim is made without adequate justification.
In Section 5.5, it is claimed that there is “optimal usage of communication bandwidth between individual cores and tester”. This claim is not justified since a heuristic solution is being used.
7. How the proposed results can be used in practice? How do they extend the forefront of the corresponding research discipline?
The results presented this thesis can be easily applied to real-life integrated circuits, as demonstrated by simulations for industry designs. The collaboration with Mentor Graphics has ensured that the practical aspects of the thesis are very strong and the solutions developed here have considered practical constraints and applicability to realistic scenarios.
In view of the strong applicability of this research to today’s problems (and tomorrow’s emerging problems as well), I consider this thesis to have significantly extended our knowledge in the field.
8. Please rank the thesis in accordance with one of the categories listed below:
a) the thesis does not fulfill requirements for the degree of Doctor of Philosophy as stated by the current law,
b) the thesis needs to be revised and resubmitted for further examination,
c) the thesis fulfills requirements for the degree of Doctor of Philosophy as stated by the current law (accept thesis as submitted),
d) the thesis fulfills requirements with the above average quality,
e) the thesis fulfills requirements and deserves distinction due to its award quality. √
Krishnendu Chakrabarty
