Some Aspects of High-Level Microprogramming
ACM Computing Surveys (CSUR)
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The Pica-B computer is a simple abstract machine designed to: \begin{enumerate} \item facilitate the portability of a simple single user operating environment written in BCPL. \item serve the pedagogic goal of providing a basis for teaching concepts of hardware and system architecture, systems programming and programming language design in a unified setting, and \item serve as a possible solution to the current and future software crisis caused by the advent of the micro-computer. \end{enumerate} The Pica-B is based on Richards'' Intcode machine but differs from it in the addition of an (interrupt) status register and a PDP-11 style memory map of I/O devices. The status register and hence interrupt and device handlers may be programmed in Pica-B code (an extention of Intcode) or in a version of BCPL with an added inline code facility, the so-called \underline{vile} command. An example is given of how interrupts and I/O are handled in Pica-B computer.