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Formal Modeling and Analysis of an Audio/Video Protocol: An Industrial . . .
, 1997
"... A formal and automatic verification of a reallife protocol is presented. The protocol, about 2800 lines of assembler code, has been used in products from the audio/video company Bang & Olufsen throughout more than a decade, and its purpose is to control the transmission of messages between audio ..."
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A formal and automatic verification of a reallife protocol is presented. The protocol, about 2800 lines of assembler code, has been used in products from the audio/video company Bang & Olufsen throughout more than a decade, and its purpose is to control the transmission of messages between audio/video components over a single bus. Such communications may collide, and one essential purpose of the protocol is to detect such collisions. The functioning is highly dependent on realtime considerations. Though the protocol was known to be faulty in that messages were lost occasionally, the protocol was too complicated in order for Bang & Olufsen to locate the bug using normal testing. However, using the realtime verification tool UPPAAL, an error trace was automatically generated, which caused the detection of "the error" in the implementation. The error was corrected and the correction was automatically proven correct, again using UPPAAL. A future, and more automated, version of the protocol, where this error is fatal, will incorporate the correction. Hence, this work is an elegant demonstration of how model checking has had an impact on practical software development. The effort of modeling this protocol has in addition generated a number of suggestions for enriching the UPPAAL language. Hence, it's also an excellent example of the reverse impact.
A new characterization of ACC 0 and probabilistic CC 0
"... that the Boolean AND function can not be computed by polynomial size constant depth circuits built from modular counting gates, i.e., by CC 0 circuits. In this work we show that the AND function can be computed by uniform probabilistic CC 0 circuits that use only O(log n) random bits. This may be vi ..."
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that the Boolean AND function can not be computed by polynomial size constant depth circuits built from modular counting gates, i.e., by CC 0 circuits. In this work we show that the AND function can be computed by uniform probabilistic CC 0 circuits that use only O(log n) random bits. This may be viewed as evidence contrary to the conjecture. As a consequence of our construction we get that all of ACC 0 can be computed by probabilistic CC 0 circuits that use only O(log n) random bits. Thus, if one were able to derandomize such circuits, we would obtain a collapse of circuit classes giving ACC 0 = CC 0. We present a derandomization of probabilistic CC 0 circuits using AND and OR gates to obtain ACC 0 = AND ◦ OR ◦ CC 0 = OR ◦ AND ◦ CC 0. AND and OR gates of sublinear fanin suffice. Both these results hold for uniform as well as nonuniform circuit classes. For nonuniform circuits we obtain the stronger conclusion that ACC 0 = rand − ACC 0 = rand − CC 0 = rand(log n)−CC 0, i.e., probabilistic ACC 0 circuits can be simulated by probabilistic CC 0 circuits using only O(log n) random bits. As an application of our results we obtain a characterization of ACC 0 by constant width planar nondeterministic branching programs, improving a previous characterization for the quasipolynomial size setting. I.