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Performance modeling and analysis of asynchronous pipelines for designers
Graduation date: 1997Better performance has been one of the main motivations behind the recent resurgence\ud
of interest in asynchronous circuits (no matter whether this is always true or not).\ud
We are particularly interested in the performance of pipelines since they are used extensively\ud
in current digital systems. There exists an algorithm that can find the exact upper\ud
and lower bounds on the separation time of events in a certain class of process graphs.\ud
However, some transformations and complex mathematical analyses, such as graph decomposition\ud
for infinite unfolded process graphs must be employed in order to reach\ud
exact bounds. This algorithm may be a good candidate for the application of CAD tool\ud
development and circuit synthesis, but it tends to block designers from visualizing what\ud
factors really affect the performance of asynchronous circuits.\ud
In this thesis, a simple approach is adopted to approximate the performance\ud
bounds. Since our method is a symbolic approach instead of a numerical approach, it\ud
allows designers to analyze the circuit performance while providing design guidelines\ud
and approaches at the same time. Our approach has two steps. First, several basic\ud
modules are chosen, including FIFO, Fork, Join, Toggle/XOR, Arbiter/Call and Select/XOR. The individual output loop delay, equivalent input delay and equivalent output\ud
delay are derived based on the Equal loopdelay theorem. The result is a set of difference\ud
equations. The performance approximation can be obtained with simple mathematical\ud
operations on the difference equations, given the bounds of stagedelays. That is,\ud
the performance bounds of output loop delay, equivalent input delay and equivalent output\ud
delay can be represented as the bounds of stagedelays. Second, for a larger system\ud
consisting of those basic modules, its performance bounds can be derived directly from\ud
the bounds of output loop delay, equivalent input delay and equivalent output delay of\ud
those basic modules which have been obtained already. This approach allows a fast and\ud
easy calculation of performance bounds, avoiding the need to rederive the difference\ud
equations for the whole system. Both modular design and performance approximation\ud
are possible with our approach