Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

Software Architectural Transformations 475
preserves the required functionality. Given the initial configuration we
can find an energy-optimized configuration by performing a series of
functionality-invariant transformations on The effects of these transformations
can be analyzed in the following manner.
Given a software architecture configuration and a transformation
a new configuration is created. Transformation has to be
underscored by and because its specific moves are defined based on
the knowledge of and The equation relating the energy consumption
of these two configurations is:
where
denotes the energy change incurred by performing transformation
In the next sub-section, we will show how
can be estimated
for the selected set of transformations we are interested in.
3.4. Energy change estimation for the transformations
In theory, a software architecture transformation can relate any two
arbitrary software architecture configurations and However, the actual
change we are going to introduce at every transformation step can be incremental,
by choice. Such a restriction to the use of atomic transformations at
every step can make the estimation of
easier if the change is
localized. That is, at every transformation step, only a small subset of all the
components (processes) in configuration is involved. By this restriction,
we can make the following approximation:
where M is the incremental move that carries universal definition, instead of
being tied to or
By decoupling move M from the actual configuration, we are able to
estimate using high-level energy macro-models specific to properties of
the architectural style we have chosen. In our case, since the style of choice
is OS-driven, the high-level energy macro-models are actually characteristics
of the OS. An energy macro-model is a function (e.g., an equation) expressing
the relationship between the energy consumption of a software function and
some predefined parameters. In the above-mentioned context, these energy
macro-models are called the OS energy characteristic data [21]. The OS energy
macro-models proposed in [21] show on average 5.9% error with respect to
the energy data used to obtain the macro-models. This level of accuracy is
sufficient for relative comparisons of different transformations.
Basically, the OS energy characteristic data consist of the following:
The explicit set: These include the energy macro-models for those system
functions that are explicitly invoked by application software, e.g., IPC