required by the control laws. A so-called control-scheduling co-design is
performed. Decisions made in the real-time (RT) software design affect the
control design, and vice versa. For instance, different SW scheduling policies
have different impacts on the latency distributions in the control loops and,
consequently, on their performance. Also, the control-loop performance directly
affects (by constraining) the SW execution parameters (i.e., sampling periods,
task-execution jitter, etc.).
In the second domain the HW engineers design an HWplatform that will
execute the control SW. The connections of all the sensors and actuators to the
platform are made via the available communication channels. However, because
the HW platform is designed separately, control engineers cannot estimate its
impact on the control-loop performance. For instance, the data from sensors and
to actuators can pass through one or more communication channels. A HW
engineer can, in general, choose from among a variety of communication
protocols, and each type introduces different latencies and jitter, which therefore
affects the SW execution. The control engineer cannot, however, evaluate the
effect of these latencies before the system is actually implemented. Hence, the
desired performance of the system may not be achieved, and it is necessary to
change and tune the control laws (calibration phase) in order to compensate for
the impact of these communication and execution delays. The fact that the
calibration has to be performed on an actual plant can be very expensive and
time-consuming, especially when the desired performance cannot be achieved
using the current HWplatform and a redesign is required. Another shortcoming
of traditional ECS design is the inability of control and SW engineers to exploit
some of the advantages offered by modern HW technologies. For instance,
control loops running in parallel, instead of the traditional sequential execution,
could give better performance. Parallel execution can be achieved with the use
of multi-processor or distributed platforms.
Modern ECS design techniques rely heavily on system modeling, which