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Let ( F’l, Pz, . . . . Pm) be a network of n finite state machines, communicating with each other asynchronously using typed messages over unbounded FIFO channels, In this paper we present a data flow approach to analyzing these communicating machines for nonprogress properties (deadlock and unspecified reception). We set up flow equations to compute the set of pending messages in the queues at any given state of such a network, The central technical contribution of this paper is an algorithm to compute approximations to solutions for the ensuing equations We then show how these approximate solutions can be used to check that interactions between the processes are free of nonprogress errors. We conclude with a number of example protocols that our algorithm certifies to be free of nonprog-ess errors. Included in the examples is a specification of X25 call establishment/clear protocol

This letter describes the first system level test vehicle in Josephson technology. The experiment consists of four circuit chips assembled on two cards in a high density, 3-dimensional, card-on-board package. A data path, which is representative of a critical path of a future prototype processor, was successfully operated with a minimum cycle time of 3.7ns. The path simulates a jump control sequence and a cache access in each machine cycle. This experiment incorporates the essential components of the logic, power and package portions of a Josephson technology prototype.