Real-time computer system with multitasking supervisor for building access control or the like

摘要

A method is disclosed for providing a single-tasking disk operating system with multitasking capability in a real-time computer system for building access control or the like. A number of reentrant, terminate-and- stay-resident application programs are loaded into a host microcomputer. As each application program loads, it passes its unique code segment and instruction pointer parameters to a look up table. For the last application program to be loaded, the program segment prefix of the application program residing in the disk operating system is copied and stored. When a timer interrupt prompts the program switching logic, the code segment and instruction pointer parameters of the then- executing program are compared with the values in the look-up table. If no match is found, program switching is postponed. If a match occurs indicating one of the application programs is then executing, a switch is permitted if the current program segment prefix matches the stored copy, thus providing fast switching when permissible.