Method for reducing control store space in a vlsi central processor

Abstract

In order to reduce the size of the memory employed to store firmware, the firmware is written in virtual control words which are then reduced by allotting them to a primary control word memory and at least one secondary control word memory which is addressed by a field in the primary control word memory. A virtual set of secondary control words are each divided into a plurality of fields, and each field of each secondary virtual control word is marked as guarded or 'don't care'. If a field is marked as 'don't care', the function represented by the virtual control word will perform properly no matter what the content of that field. Virtual control word pairs are then examined to ascertain if they can be combined into a single control word. If the guarded fields in the first virtual control word align with the 'don't care' fields in the second virtual control word and vice versa, the two virtual control words can be combined into a single control word containing the contents of the guarded fields from both virtual control words, the remaining fields, if any, remaining 'don't care'. This process may be reiterated to determine if the combined control word can be further combined with another virtual control word. In operation, all the functions represented by a combined control word are executed by calling for that single control word stored in the secondary control word memory.