An apparatus for a low energy accelerator processor architecture is disclosed. An example arrangement is an integrated circuit that includes a system bus having a data width N, where N is a positive integer; a central processor unit coupled to the system bus and configured to execute instructions retrieved from a memory; a low energy accelerator processor configured to execute instruction words received on the system bus and having a plurality of execution units including a load store unit, a load coefficient unit, a multiply unit, and a butterfly/adder ALU unit, wherein each of the execution units is configured to perform operations responsive to retrieved instruction words; and a data register file comprising a set of data registers coupled to the plurality of execution units, wherein the registers are coupled to selected ones of the plurality of execution units. Additional methods and apparatus are disclosed.