CPU with integrated multiply/accumulate unit.

摘要

An integrated circuit processor architecture that implements digital signal processing (DSP) functions with less hardware, improved speed and a more efficient layout. The CPU resources are used in conjunction with an integrated multiply/accumulate unit to perform DSP operations. Use of the CPU's internal register for the circular buffer of the DSP multiply/accumulate function allows a minimum amount of lower speed hardware to be used for the multiply/accumulate unit and permits DSP operations to be performed in parallel. The multiply/accumulate unit takes advantage of the inherent accumulating properties of conventional multiplier designs to perform multiplication of two signed binary numbers using the modified Booth's algorithm but in both reduced cycle time and hardware requirements. This is accomplished by using the adder within the multiplier to sum the product terms. Instead of clearing the adder of the result of one multiplication before beginning another, the result is maintained and all subsequent partial products are added to it to generate a final output. The placement of the 32-bits of the multiply/accumulate unit's multiplicand register is arranged in two rows of 8 even bits and two rows of 8 odd bits to allow left shift by two with a single loop around and to provide direct interface with the 16-bit data latch register on its input and the rest of the 32-bit ALU on its output. The multiply/accumulate unit's multiplexor uses tri-state inverters rather than couplers to provide compact layout and drive capability for speed. The multiply/accumulate unit also utilizes a fully static 32-bit ALU with two stage carry by-pass. The four transistor static carry claim places minimal loading on the chain. The multiply/accumulate unit generates mutually exclusive sticky flag bits that represent a signed arithmetic overflow of the product data. Once one of the sticky flag bits has been set true, the other cannot be set true until both have been reset. <IMAGE>