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of the sub-tile by means of the supporting element. This, in turn, will trigger an
update event over the sub-tile, if any, connected to the first one by means of the
output port. By following the very same process, the information is propagated
inside the structure, only where it is needed.
There could be an active device inside the sub-tile, and the propagation of
information could lead to a change in its status. Should this happen, another kind
of event would be enqueued in the event queue, waiting to be processed to take
into account a possible change of information in a direction of propagation that
is orthogonal with respect to the one that originated the event. This approach
is very flexible, indeed, because it allows for different kind of control of dynamic
circuits (number of phases) since the phase sequence is not embedded into the
simulator but is coded in the input control sequence and the same approach can
thereby be used in many different scenarios.
References.
The literature about NanoArray is quite wide, here some references
are reported for interested readers. In [
59
,
60
] some of the work of University of
Massachusetts Amherst is reported. Other solutions were proposed by Likharev
[
61
], Dehon [
62
], a group of HP [
63
] and the Carniege Melon University [
64
].
11 Conclusions
In this chapter we have described ToPoliNano, a tool which aim is to design and
simulate NML circuits and other emerging technologies following the same top-
down methodology used in the CMOS case. This tool allows to easily describe
and simulate complex NML circuits without loosing important details like the
placement of each magnets, as it happens in case of VHDL modeling, and without
the limitations in terms of speed and circuit sizes of low level simulators.
The tool is still in development so it does not have all the planned functional-
ities but we are still working hard on completing and improving it. Particularly
our efforts are oriented in three directions: Custom circuits description, Place &
Route algorithm and simulation engine.
While the automatic layout generation is a very important feature, we
acknowledge that also the manual custom circuit description plays an impor-
tant role. We are therefore trying to improve the means available to describe
circuits manually, for example providing an interface that allows to import
circuits designed with QCADesigner, opportunely converted substituting
magnets to the QCA cells used by QCADesigner. This can represent an impor-
tant step in the tool development, since many researchers in the QCA com-
munity use QCADesigner. We are also working to modify the program to be
released to other people that work in this field, so that they can fully exploit the
advantages given by ToPoliNano.
The Place & Route algorithm is the program core and also the most complex
part. We are working in two directions, to improve the algorithm allowing it
to handle also sequential circuits and implementing a floorplanning algorithm
to create the layout of complex circuits with a hierarchical structure. Sequential
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