GE PACSystems RXi User Manual

Chapter 5. CPU Operation78 PACSystems* RXi Distributed IO Controller User Manual GFK-2816F5.2 Program Scheduling ModesThe CPU supports one program scheduling mode, the Ordered mode. An ordered program isexecuted in its entirety once per sweep in the Logic Window.5.3 Window ModesThe previous section describes the phases of a typical CPU sweep. The ControllerCommunications, Backplane Communications, and Background windows can be run invarious modes, based on the CPU sweep mode. (CPU sweep modes are described in detailon page 75.) The following three window modes are available:Run-to-CompletionIn Run-to-Completion mode, all requests made when the window has startedare serviced. When all pending requests in the given window have completed,the CPU transitions to the next phase of the sweep. (This does not apply to theBackground window because it does not process requests.)Constant In Constant Window mode, the total amount of time that the ControllerCommunications window, Backplane Communications window, andBackground window run is fixed. If the time expires while in the middle ofservicing a request, these windows are closed, and communications will beresumed the next sweep. If no requests are pending in this window, the CPUcycles through these windows the specified amount of time polling for furtherrequests. If any window is put in constant window mode, all are in constantwindow mode.Limited In Limited mode, the maximum time that the window runs is fixed. If timeexpires while in the middle of servicing a request, the window is closed, andcommunications will be resumed the next time that the given window is run. Ifno requests are pending in this window, the CPU proceeds to the next phase ofthe sweep.