Software Issues in Wireless Sensor Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 31

Fig. 3.1 A comparison of sensor nodes and personal computers

3.1 The Full Custom Approach

The “full custom approach” - programming a sensor node as if it was an ordinary
embedded device - will not be described here in detail; we will rather concentrate
on the pros and cons of this approach when used for sensor networks.
The full custom software approach means that we do not use an operating system;
we program the sensor node's processor directly, using assembly language. Another
option is to use a microcontroller-adapted high-level language (such as Keil C).
Either way, we would have to operate the peripherals directly, using control and
status registers, rather than primitives provided by an OS. The completed program
would then be loaded into a sensor node's ROM, and executed when the device is
powered on. With the full custom hardware approach, we go one step further and
design the custom hardware for the application, rather than use readymade sensor
modes.
A program developed with “full custom” would probably be the fastest and would
consume the least battery power, as the whole functionality is optimized for the
particular application which is developed. However, programming itself would be
quite hard, and even attaining basic functionality of the application would take a
long time.

3.2 The Scaled Traditional Approach

With the “scaled traditional approach” the sensor node is programmed with the
same philosophy as when programming the personal computer: OS primitives are
used to achieve hardware abstraction. Still, due to scarce, scaled resources of a sensor