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Fig. 16.
Layout of a 6 bit Ripple Carry Adder.
5 Simulation Engine
After obtaining the detailed circuit layout it is important to simulate it to ver-
ify its behavior and to evaluate its performance. For this purpose a behavioral
simulation engine was developed to be used in ToPoliNano. In order to simu-
late the circuit the graph used to represent the circuit must be modified. The
hierarchical graph structure, which describes the circuit, is flattened by the sim-
ulation engine. A completely new data structure based on a dynamical matrix
is created, in this way all physical information are kept (magnets positions) and
the structural ones are discarded.
An example of simulation matrix is shown in Fig.
17
. It represents a majority
voter but the structural information are lost so it is seen simply as a matrix
containing or not containing magnets in each cell. Three different type of magnets
can be identified: input, output and normal. Every magnet is seen as a tristate
device, because it can assume only three values, '0', '1' and RESET.
5.1 Simulation Algorithm
The behavior of the simulation algorithm has been captured and encapsulated
in a finite-state machine (FSM). The clock waveforms Fig.
18
(A) can be divided
in 6 defined states and are therefore mapped to the FSM shown in Fig.
18
(B).
The initial state is represented by the 0, while the first transition depends
on the clock signals behavior. For example, the transition to the state 1 takes
place when the first clock signal is equal to one and the second and the third are
equal to 0. The FSM cycles through the states because of the periodic behavior
of the clock waveforms. In order to manage transitions, the future step
S
f
can
be calculated starting from the present state
S
p
(Eq.
1
):
S
f
S
p
+1)
mod
=(
6
(1)
The general simulation algorithm follows the FSM switching periodically through
its states. In each state, the value of each magnet must be calculated depending
on the clock zone in which it is located. In particular, all magnets belonging to
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