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Q-modules are internally-clocked modules that can be used to satisfy delay-insensitive specifications. The allowed changes of inputs to, and outputs from, a delay-insensitive module are specified by partial orderings of these signals in such a way that the set of possible behaviors remains unchanged with arbitrary values of delay inserted in series with each input and output path. A two-phase single-wire clock and a single-wire clock acknowledge are used for sequence control and accommodate any value of flip-flop hold time. The clock distribution within a Qmodule is also delay insensitive and the modules will operate correctly with any value of delay inserted in series with the clock distribution. Metastable flip-flop operation due to input signal changes will not cause failures hut will only extend the clock cycle time. Correct sequence operation is ensured in exchange for an occasional clock cycle extension. The only delay constraint that must be satisfied in assembling a Q-module from its predesigned components is a one-sided requirement that a particular clock phase be longer than the longest delay through the combinational logic of the module. Prototypes of components to implement Qmodules have been designed, and a design aid program, QSYN, to place instances of these components, personalize a PLA, and generate a MAGIC or CIF file for a CMOS realization, including the delay circuitry, is being developed. Testability is one of the advantages of Q-modules over clock-free delay-insensitive modules; circuitry is included in the cells for testing the logic and interconnections.

This report describes the design and implementation of a gigabit ATM switching system supporting link rates from 150 Mb/s to 2.4 Gb/s, with a uniquely e cient multicast switch a r c hitecture that enables the construction of systems with essentially constant per port costs for con gurations ranging from 8 to 4096 ports and system capacities approaching 10 Tb/s. The system design supports many-to-one and many-to-many forms of multicast, in addition to the usual one-to-many. It also provides multicast virtual paths, constant time con guration of multicast connections and an e cient p a c ket-level discard method, that can achieve 100% link e ciencies, without large bu ers.

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