Design and Implementation of TinyGALS: A Programming Model for ...

unlike Click, the TinyGALS model does not contain a task queue. 15
Pull processing in sensor networks Although TinyGALS does not currently use pull
processing, the following example by Jie Liu given in [42] illustrates a situation in which
pull processing is desirable for eliminating unnecessary computation. Figure 25 shows a
sensor network application in which four nodes cooperate to detect intruders. Each node
is only capable of detecting intruders within a limited range and has a limited battery life.
Communication with other nodes consumes more power than performing local compu-
tations, so nodes should send data only when necessary. Node A has more power and
functionality than other nodes in the system. It is known that an intruder is most likely to
come from the west, somewhat likely to come from the south, but very unlikely to come
from the east or north. Under these assumptions, node A may want to pull data from other
nodes only when needed. Figure 26 shows one possible configuration for this kind of pull
processing. The center component is similar to the Click scheduler element. This example
also demonstrates a way to perform distributed multitasking. Node D (and others) may be
free to perform other computations while node A performs most of the intrusion detection.
This could be an extension to the current single-node architecture of TinyGALS.
North
A D
B C
Figure 25: A sensor network application.
15 Although, for backwards compatibility with TinyOS, the TinyGALS runtime system implementation
supports TinyOS tasks, which are long running computations placed in the task queue by a TinyOS compo-
nent method. The scheduler runs tasks in the task queue only after processing all events in the event queue.
Additionally, tasks can be preempted by hardware interrupts. See 6.1 for more information.
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