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ENERGY CONTROL AND SOFTWARE 161
are better than others for this task. The point is, if the processor is designed to enable
the energy control you require, then it probably has special-purpose hardware built in.
Often, software drivers for the energy control hardware are already available. The over-
all energy control algorithm must take advantage of these processor features.
Attempting to circumvent them or to use them in nonstandard ways will likely mean
ruination. The processor designers probably had a difficult time getting things right and
it is easy to break their design. Stick to the basics and don’t be afraid to call the proces-
sor company.

CENTRALIZATION

Try to centralize the energy code. To function properly, energy control software must
often be spread over most of the software in the robot’s computer. Portions of the code
are in the flash memory boot code, the operating system, and the application code. As
the code spreads out like this, it starts to get “holes” in it. It becomes more fragile in
terms of its capability to provide proper energy control. Simultaneously, if multiple pro-
grammers are involved, programming discipline becomes more difficult. We must pro-
vide a simple, understandable application programmer’s interface (API) that will attend
to energy control properly. Fortunately, a couple of remedies are available:

Keep it tight If the API code is written from the ground up, try to keep the API
small and confined to the lowest levels of code (the Basic Input/Output System
[BIOS] and a few drivers).
Keep it simple If you must build your own processor drivers, and can get away
with it, don’t try to implement every feature the processor offers. Get the most
aggressive power-saving features of the processor working well first. If the other
features are also desirable, add them later if you can.

Now we should look at strategies for power control. Where do we start?
It makes sense to start with the specifications. While the specifications are being
written, we will probably have a sense of how difficult the energy control problem will
be. It makes sense, right then, to look at energy control in a larger sense and decide on
the overall approach. The government even has specific programs to encourage the
industry to decrease energy consumption (see www.energystar.gov).
Semiconductor companies and operating system companies work together to provide
a coordinated approach to power control. As an example, the community defining the PC
architecture has done this over the years. Committees meet once a year to ratify the
changes that all parties will make in their designs and publish documents specifying the
changes. The Windows Hardware Engineering Conference (WiNHEC) is one of these
committees (www.microsoft.com/winhec/default.mspx).