Dynamic microprogramming and external subroutine calls in a multics-type environment

A scheme is presented for external subroutine calls which makes it possible to have microprogrammed subroutines and to allow subroutines written in different languages. The languages may be compiled to different Directly Executed Languages (DELs) with corresponding microprogrammed interpreters. The scheme makes it possible to intercept each external subroutine call so that such actions as parameter validation, microprogram simulation, and statistics collection can be done. The scheme is intended to be working in a Multics-type environment with late dynamic linking, virtual memory, and ring protection. The scheme is adapted to a model of microprogram development which is also presented.