Pseudo zero cycle address generator and fast memory access

Abstract

A method and apparatus estimate the memory address needed for a low level programming instruction in reduced instruction set computing systems. Taking advantage of a known computing environment and data architecture, bits from a displacement field in an Instruction Register may be combined with bits from a Base Register through hardware logic circuitry, preferably performing a mathematical computation such as addition. Together with bits gated directly from the Base Register and the displacement field, the combined bits form an estimate of the effective address of the desired memory location. The estimation is performed early in an instruction cycle, and therefore allows data from the memory, preferably a Data Cache, to be available at the end of the next instruction cycle, thus producing the address in what appears to be zero cycles. The method and apparatus avoid stall conditions from the CPU, and are particularly useful for Very Long Instruction Word architecture.