The proposed generic top-level SUD structure depicted in the following figure is the most frequently used in control unit designs with Rational Statemate.
At this level the SUD is partitioned into hardwired/bus I/O-functions and application related main system functions (Firmware, Diagnostics, Control Algorithm, etc.).
Note: No initialization functions are represented at this level. Such functions are considered to be an implementation detailThe functionality captured in the input processing block (INPUT_PROC) could be: signal filtering, switch debouncing, transformation of electrical signals to physical or logical values, etc.
Details of bus protocols are not considered in a functional model. Therefore the receive/transmit functionality within the bus interface is confined to checking for changes on the bus and mapping them to internal variables, or formulating the messages for output onto the bus on changes of respective internal variables; e.g:
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●The data-store (PROCESS_BFFR) in the generic structure might be interpreted either as a data repository or as an “internal bus.” In the latter case the communication between the functions connected to the “internal bus” should be modeled as outlined in Modeling Bus Communication.
Note: At this stage it is not necessary to define elements of the internal information flows. Instead, you can define them when the system behavior is captured (typically starting at hierarchy level 2).