Modosk: a modular distributed operating system kernel for real-time process control

The operating system kernel of a multiprocessor system based on 16 bit microcomputers is described. The multiprocessor system constitutes a node of a local computer network dedicated to the control of continuous or discontinuous industrial processes. The kernel makes available a virtual machine where processes allocated on different processors are executed in parallel, while processes which reside on the same processor are executed in a multitasking environment. The processes can cooperate by means of synchronization and message passing primitives; furthermore they can interact by means of short-term scheduling primitives which perform the creation, destruction, activation and termination of a process. The interprocessor communication mechanisms allow the primitives to make all process interactions transparent to the physical allocation of the interacting processes. The system has been completely implemented in the PASCAL language, excepting only few functions of the lowest level, coded in the assembler language. The distributed kernel has been developed and tested on a conventional monoprocessor machine (a DEC PDP11/34 computer under RSX11-M Operating System). Successively it has been transported on a microprocessor development system, where its time and space requirements have been evaluated.