[Top] | [Previous] | [Next]

4.2.2 Control Flow Diagram Example

Figure 8 shows a CFD for Commanding. This CFD consists of ovals indicating functions, and arrows indicating flow of control. In this example, each flow completes before the next one begins, indicating the nominal ordering of Commanding activities. If real-time commanding is required, the distinction between pre-contact and post-contact activities may be eliminated.

Timing for Commanding involves three separate periods: system configuration, pre-contact, and contact; so the CFD shows three separate axes for these time periods.

Figure 8. Commanding control flow diagram.

Figure 8 contains the critical functions performed by Commanding. Note that these functions show lower-level functions not present in Figure 7. For example, the subfunctions Select Commands, Check Constraints, and Transmit Commands comprise the function Process and Transmit Commands in Figure 7. For a description of these lower-level functions, see Appendix C.

The diagram shows a linear sequence of Commanding related functions required well before a contact. A separate sequence of functions is repeated before each contact. During contact, a linear sequence of functions is performed for each command or command block. This sequence is repeated for each command in the command plan during the contact. This CFD represents the processing flow for the typical synchronous commanding mode. Each function completes before the next one begins. For the less typical asynchronous commanding mode, the post-command check and evaluations may be performed concurrently with command selection and transmission. This mode would require a separate CFD.