PARALLEL COMPUTING WITH SPIN WAVES - Bio-Inspired and Nanoscale Integrated Computing - page 232

8.3. PARALLEL ROUTING AND BROADCASTING
In the following section, we illustrate the routing features of our three spin-wave
architectures. We focus primarily on the routing on a spin-wave crossbar, and we
explain how the routing on the other two architectures differs from the routing on
the crossbar. We also discuss the enhanced multiple multicasting feature on the
fully interconnected cluster.
8.3.1. On Spin-Wave Crossbar
Our spin-wave crossbar has several parallel and fault tolerant routing features [9].
We concentrate the routing features of this architecture in three different
scenarios. These techniques are then compared to those for the reconfigurable
spin-wave architecture and the fully connected spin-wave architecture.
It is well known that all crossbars are capable of realizing any arbitrary one-
to-one permutation. In a standard VLSI crossbar, however, unless there are
broadcasting buses on each row, at any single point in time, only one switch is
turned on in each row and each column. Spin-wave crossbars, on the other hand
support additional features such as broadcasting and concurrent receiving as
described below.
A RBITRARY P ERMUTATIONS . Similar to any standard crossbar, a spin-wave
crossbar realizes arbitrary permutations. As described in the previous section, in
the crossbar architecture the signals are directed in each row and each column
through spin-wave buses. As an example of a one-to-one permutation realization,
assume that input 3 needs to send a message to output 6. In that case, the switch in
row 3 and column 6, represented as s(3,6) should be set to on. In addition, the
receiver's frequency of node 6 should be tuned to sender's frequency of node 3.
The switches can be set to on according to the following mechanism: A fixed
frequency is assigned to each column, and on top of each switch there is a receiver
that is tuned to the frequency assigned to its column. As soon as the switch
receives a signal on its frequency, it is activated and can route the data. For
instance, switch s(3,6) is tuned onto the frequency assigned to column 6, f 6 . Input
node 3 sends a signal on frequency f 6 on row 3, which turns on s(3,6). Now, the
third row is connected to the sixth column, and permutation (3,6) is realized.
Figure 8.5 shows this communication on a crossbar of size 6. Note that there is a
switch located on each of the grid points, but here we are just showing the
activated one.
C ONCURRENT R ECEIVE F EATURE . Realizing concurrent receive feature is very
similar to realizing the one-to-one permutation described above. A fixed frequency
is assigned to each column (each receiver), and the senders tune their sending
frequency to that frequency. As explained in the previous section, one of the
important features of a spin-wave crossbar is allowing concurrent write. For
instance node 2, 3, and 4 can all send a message to node 5, as shown in Figure 8.6.