Technology of Test Design: DFT & TFD
DFT &TFD
The offered technology is transparent thereof it explains to customer from
what parts does a test quality consist of:
· Is the project verified ?
· Do the buses and bidirectional ports work correctly ?
· Is the circuit sufficiently testable to
generate the test automatically ?
· Whether is there no redundancy interfering
achievement of high quality?
To answer the above questions the source circuit is analyzed and the
designer receives:
When designer will realize testable modifications he will receive
Essence of technological stages in brief is as following::
Analysis of source circuit and forecast of test quality
Further all about the sample circuit named as "FLEXER"...
..but here may be analyse of your own circuit be placed..
DFT Report - about testability of source circuit FLEXER
Let's construct area of |
Brown internal circle - 60 % from total 100 % of bits |
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Let's construct area of |
Blue internal circle – 50% from total 100% of bits |
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Let's construct |
The optimistic forecast of test quality only 29% |
The red area makes |
Estimate and select the best ACPs - Additional Control Points
Let's add ACPs therof Brown area of good |
Brown area has been expanded up to 95% |
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As a consequence |
Blue area has been expanded up to 80% |
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Let's construct advanced |
Red area has been expanded up to 76% |
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Predicted quality of the test is |
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Estimate and select the best AOPs - Additional
Observation Points
Let's add AOPs, repeatedly having expanded dark blue area of good observability measures .. |
The blue area repeatedly has been expanded up to 97 % |
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Let's construct double advanced testability zone - common red area where the advanced controlability and the advanced observability measures both good |
Red area has extended up to 92% |
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The quality of the test, seems, already quite good ? Let's go next step.. |
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Generation of the verification test for a rating of influence of arising search problems on quality of the future hardware test of sample circuit FLEXER.
Let's generated verification test has reached 90% Optimistic forecast of the test quality was 92% |
There is a problem not only in testability of the project. The circuit needs in additional debugging too. |
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Thereof general forecast of the HW test quality is possible to expect at a level 83 % |
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The given percentages illustrate the fact that generation of the test is a complex problem. The matter is that at apparent propriety of impact percentages the total percentage of test quality frequently turns out unsufficient. And we here show, of what parts it develops. From this analysis also it is possible to conclude that achievement of quality close to 100 % need the exact decision of discussed intermediate tasks. According to offered technology in the Tw-CAD's report thoroughly both the problems are particularly stated and the decisions for each circuit individually are offered.
The recommendations for testability improvement and forecast of the test quality
The Tw-CAD simulates sequential points insertion and informs designer about the place and a kind of the offered recommendations for improvement of controlability and observability not just above diagrams. Offering the recommendations we do not fix a manner to realize suggested circuit modifications. Diagram predicts how does fault coverage is growing as ACPs and AOPs are been placed. Customer has a choice to plan circuit DFT modifications.
More details about all calculated measures are shown in the following table.
______________________________________________
| | measures
| PROGNOSIS of |
| # point | SUM MAX |CONTR OBSERV TESTABLE|
|_________|______________|_____________________|
| source | 368833 11885
| 87.8% 90.2% 78.6% |<==source circuit's measures
|c 1 146 | 315382 11885 | 89.6% 92.1% 81.7% |c<== Control points
|c 2 111 | 267121 11237 | 91.8% 92.9% 84.8% |
|c 3 107 | 216449 8731 | 93.8% 94.5% 88.1% |
|c 4 108 | 190229 8731 | 95.4% 94.5% 89.7% |
|c 5 110 | 167569 6502 | 96.2% 94.5% 90.5% |
|c 6 109 | 145554 6502 | 97.0% 94.5% 91.4% |
|c 7 225 | 124590 6502 | 98.2% 95.1% 93.2% |
|c 8 224 | 98368 6502 | 98.6% 97.3% 95.9% |
|c 9 106 | 81091 4247 | 98.8% 97.3% 96.1% |
|c 10 105 | 65603 2669 | 99.2% 97.3% 96.5% |
|________ |______________|_____________________|
|o 11 186 |
30254 618 | 99.2% 98.0% 97.1% |o<==Observation point,finally
|______________________________________________|
One can point out that it is more important control point insertion (10)
rather observation point insertion (1).
Besides this summary diagrams and above measures table we inform designer about following
The reached test quality does not exceed this one predicted usually.
More detailed diagram is following for another circuit which has very poor starting prognosis of 65% test quality. To reach good prognosis there are needed more number of addtional control and observation points than above real life sample.
If designer wants he can observ more detailed dagram where three curves presented as measures of
At this diagram prognosis of test quality is been improved as additional points insertion:
Please focus your attention on all-round rectangular components of test quality are discussed with suppoused measures and diagram.