Dynamic microprogramming
Allen B. Tucker, Michael J. Flynn · Communications of the ACM · 1971
A dynamically microprogrammed processor is characterized by a small (4 ~ 64-bit word) read-write "micro" storage.The access time of this storage is similar to the cycle time of the machine (50-100 nsec).This microstorage is used to contain both data and subroutines.The (micro) instructions in such a processor differ from the conventional in that they perform only purely combinatorial operations; sequencing is under the control of the microinstruction.The presence of the read-write microstorage permits a more flexible assignment of resources than the read-only storage.In particular, the processor developed in this paper stresses the simultaneous operation (within the microinstruction) of the adder, shifter, masker, and testing facilities of the processor.A microassembly language is developed and the overhead involved in subroutine linkages is analyzed.The efficiency of a flexible software linkage scheme is examined as to its overhead for various subroutine characteristics.Finally, three examples of problem-oriented programming are considered and the resulting coding is compared against a System/360 assembly language version, with the technology normalized.