INTERPIO::FSS mHlNlCATICN AND DISPA'lCHING EXAMPLE
Procedures in the utilities section demonstrate how a programmer can
construct facilities to invoke IP functions. Recall from the function sunmary in Aweooix B that an AP requests an IP function by writing a process selection index, all required operands, and finally depositing a function code into the appropriate slots in the function request facility (frf). The IP begins execution of the function only after the function code has been written. This is demonstrated by the procedures Open_window and Close_window.
The initialization section of the prog ram points out sane simplifying assumptions which are made for the ~rpose of this example. First, interrupts are disabled. This converts the three tasks of the printer example (printer server task, printer task, and printer reply task) of Chapter I into sequential tasks rather than concurrent tasks. It also makes it easier to demonstrate changes in the state of the system and illustrate them with the accompanying figures. Second, the calIon the Dispatch procedure asstnnes that only one IP process exists in the 432 system. The IP supports multiple process environments but only one is required in this example.
The print driver body contains an aggregation of code which acoamplishes the three tasks of the Chapter 1 example. Notice that the three tasks are performed sequentially.
Imbedded in the program text are references to Figures 2 through 6 which depict the state of the 432 system objects and the logical I/O processor (the IP/AP pair).
