1 Montgomery Modular Multiplication in Hard- ware

FEI KEMT
2.2.3 Interface to Controller
The way in which the MMM coprocessor is connected to the control unit (e.g. an
embedded processor) is important for the control of the computation process and
for the exchange of processed data.
Our first objective is to find a solution which would make possible a fast and flex-
ible replacement of input and output data between the memory of the host processor
and the MMM coprocessor’s internal memory block. The requirement for flexibility
is related to the scalability of the coprocessor that may include several MMM units.
Moreover, the internal word widths of the control unit and the coprocessor may
differ.
Other goal is to optimise the control of the coprocessor(s). The triggering of
the computations and then checking their status plays important role especially in
configurations with several coprocessors (not necessarily the MMM coprocessors)
operated by one control unit when it is ineligible to block the operations running on
the host processor.
Finally, the goal is also to design an interface that would be universal and ap-
plicable with minimal amount of a clue logic for connection to different types of
processor buses.
The interface that satisfies the requirements mentioned above is depicted in
Figure 2 – 7. The functionality of the particular signals is explained in the next part
of the section.
clock
reset
chip select
write enable
irq
address bus
data bus
MMM
coprocessor
Figure 2 – 7 Proposed universal interface for the MMM coprocessor
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