
System-Level Design 153
With these additions, the system modes and priorities are sufficiently
defined for the design.
The only functions that haven’t been specified are those functions
that fall into the category of housekeeping functions. These functions
have no specific timing or priority; rather, they are just executed when
execution time is available. This could be because their typical timing
is infrequent compared to other higher priority functions, or it could
be that they are run as a sort of preventive maintenance for the system.
Typical examples of this kind of function can include the following:
1. Periodic checks of the voltage of ...