Sharing of register stack by two execution units in a central processor

Abstract

In a central processor incorporating at least one co-processor, such as a floating point arithmetic co-processor, in addition to a basic arithmetic logic unit, the problem of rationalizing the contents of the accumulator and supplementary accumulator registers without the burden of speed penalties is addressed and solved. This is achieved by providing input/output access to a common register file and by switching control of the register file to the proper processing unit appropriately. A single, shared accumulator register and a single, shared supplementary accumulator register are included in the stack along with other sharable registers such as address modification registers. Thus, the contents of the accumulator register and the supplementary accumulator register are always up-to-date and available to all processing units in the central processor without the need for first carrying out rationalization steps.