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180 CHAPTER SEVEN
Pipelines for Speed
In Chapter 3 on computer hardware, we discussed using pipelines to speed up process-
ing. The specific example used was “If A, then B, else C.” In a pipeline optimized for
speed, A, B, and C are put into the pipeline simultaneously and are computed simulta-
neously. Either B or C comes out of the pipeline (already precomputed) based on the
value of A. This is the way a pipeline optimized for speed would behave. It burns energy
as fast as possible.

Pipelines for Power

As the processor goes about executing the instructions inside the pipeline, it sometimes
notices that some of the instructions don’t have to be executed. Power can be saved if
unneeded instructions are not executed. Let’s revisit our example program, “If A, then
B, else C.” In a pipeline optimized for power, A is put in the pipeline and computed
first.Based on the value of A, either B or C is put into the pipeline for computation.
This method is clearly slower but saves the energy that might be used in unneeded
computations.
We just looked at how a pipeline in a processor can be optimized for energy conser-
vation. The processor has a pipeline that handles instructions that are executed in a serial
manner. In the same manner, we can construct a pipeline of tasks that the robot executes
in a serial manner. If we buffer up these tasks instead of executing them immediately,
we may discover tasks that do not have to be executed. In a real operation, various com-
mands may arise that just don’t make sense. One set of commands might look like this:
“Go to from Point B to Point C and pick up the Rock C. Bring it back to Point B and
examine Fact A. If A is true, drop Rock C and pick up Rock B.”
A properly constructed robot task pipeline would look at this series of commands and
alter it to the following: “Examine Fact A. If A is true, pick up Rock B, or else go to
Point C and pick up Rock C.”
A very well constructed robot task pipeline would question whether the robot should
do any of this work. If neither the information about fact A nor the rocks are needed in
subsequent tasks, all this work can be avoided. If a subsequent robot task requires Rock
B or Rock C, then the pipelined tasks can be executed. Further, the robot task pipeline
can determine if the robot really needs to return to Point B at all.
Most people, while cleaning house, will find lots of reasons to go upstairs and down-
stairs to achieve specific goals. If no emergencies occur, it makes sense to pipeline all
the tasks for a while. Go upstairs for the upstairs tasks and downstairs for the down-
stairs tasks. It’s easy to tell that this saves energy. If the robot can afford to hesitate for
a while, it can pipeline its tasks and probably save some energy.