Image Processing Reference
In-Depth Information
Wireless Vibration Monitoring Case Example
In the reference case, the chosen communication solution, i.e., DUST Networks SmartMesh XD
chip, provides a complete SoC solution, where both the hardware and software are hidden within
the chip.
However, a small portion of the communications interface resides outside the SoC component,
possibly in the application. This is functionality which handles packet preparation, such as byte
stuffing and Frame check sequence (FCS) calculation for packets which will be transmitted, and
the corresponding operations for received packets.
This means that we need to implement communication-related functionality in the application,
which normally would be considered to be part of the protocol stack.
Modularity can also be achieved at a lower level. For instance, the communication protocol can
be seen as consisting of several blocks, known as the OSI layers. Given a healthy design procedure,
one may be able to exchange a single layer with one from a different source. Obviously, the more the
code is split up, the more modular it becomes. At the same time, the risk of suboptimizing increases,
i.e., the modules are optimized (with respect to power, performance, code size, etc.) individually, but
this does not necessarily give a globally optimum solution.
27.8.1.3 Lifetime
Industrial automation devices have a life expectancy that could be measured in ths of years. This
puts a lot of demand on a modular and flexible design, which is easily maintained. Even if the device
functionality would not change over its lifetime (which is highly unlikely), we still need to cope
with availability of components. For certain parts of a WSN device, where the technology changes
more rapidly, this is especially critical. For example, the sensor part (see Figure .) evolves quite
slowly, whereas the radio and power source technologies evolve very quickly. This fact warrants a
high degree of modularity around the radio solution, something that is not always advantageous
from a performance point of view.
27.8.2 Interfaces
The key to achieving a good modular design, and thus being able to reuse components, are the com-
ponent interfaces. The interface provides an abstraction of the component, i.e., a separation of the
external communication with the component from its internal operations. his abstraction enables
the internal modification of a component without affecting how the rest of the device is operating or
interacting with the component.
A well-defined interface allows for easy maintenance and reuse of the component, but since inter-
faces are a form of indirection, some additional overhead and decreased performance is incurred vs.
direct communication. A modular design can thus introduce extra overhead in the sense of proto-
cols needed to communicate between the different components (using the interfaces), which leads
to increased power consumption and can result in bottlenecks in the system. he reason is that the
system can only operate at the “speed” of its slowest component, at least if that component is part of
the central functionality of the system.
Reusing and exchanging integrated circuits (ICs) requires that their interfaces are compatible with
each other. his is commonly called pin compatibility, and comprises
•
Functional compatibility: implies that two ICs have the same functions (inputs, outputs,
power supply, ground, etc.), assigned to the same pins
•
Mechanical compatibility: ensures that ICs can be inserted into the same socket or
soldered to the same footprint
•
Electrical compatibility: implies that the components work with the same supply and
signaling voltage levels
