Low energy accelerator processor architecture with short parallel instruction word and non-orthogonal register data file

1. An integrated circuit, comprising:

a system bus for transferring data between memory devices, processors, and peripheral devices having a data width N, where N is a positive integer;

a central processor unit coupled to the system bus;

a low energy accelerator processor coupled to the system bus and having a plurality of execution units;

a register file comprising a plurality of registers in a non-orthogonal arrangement with the low energy accelerator processor;

a first execution unit of the plurality of execution units configured to read data from and write data to each of the registers and execute a Fast Fourier Transform; and

a second execution unit of the plurality of execution units configured to read data from only a first subset of the registers and write data to only a second subset of the registers, wherein the first subset comprises a fewer number of registers than the second subset.

2. The integrated circuit of claim 1 , wherein the low energy accelerator processor includes a floating point flag register to indicate if at least one of the first and second execution units operates on floating point or fixed point data.

3. The integrated circuit of claim 1 , wherein the first execution unit is a butterfly/adder ALU unit configured to perform Finite Impulse Response filtering.

4. The integrated circuit of claim 1 , comprising a third execution unit of the plurality of execution units configured to read data from only a third subset of the registers and write data to only a fourth subset of the registers.

5. The integrated circuit of claim 4 , wherein the third subset comprises the same number of registers as the fourth subset.

6. The integrated circuit of claim 1 , wherein the second execution unit is a load store unit of the low energy accelerator processor, the second execution unit being configured to use at least four of the registers as destination registers.

7. The integrated circuit of claim 1 , wherein the low energy accelerator processor is configured to execute the Fast Fourier Transform in response to a 32-bit instruction word.

8. The integrated circuit of claim 1 , wherein the data width N is 32 bits.

9. The integrated circuit of claim 1 , wherein the register file is included with the low energy accelerator processor and directly accessed by only the plurality of execution units.

10. The integrated circuit of claim 1 , wherein the low energy accelerator processor comprises a loop count register, a loop start register, and a loop end register configured to control a repetitive loop operation.

11. The integrated circuit of claim 1 , wherein none of the registers of the first subset are also part of the second subset.

12. The integrated circuit of claim 11 , comprising a third execution unit of the plurality of execution units configured to read data from only a third subset of the registers and write data to only a fourth subset of the registers, wherein at least some of the registers of the third subset are included in the second subset, and wherein none of the registers of the fourth subset overlap with registers of the first subset, the second subset, and the third subset.

13. The integrated circuit of claim 1 , comprising a fourth execution unit configured to write data to only a fifth subset of the registers and further configured to not read data from any of the registers.

14. A data processor, comprising:

a system bus coupled to at least one memory and having a data width of N, where N is a positive integer;

a central processor unit coupled to the system bus;

a low energy accelerator processor having a plurality of execution units, coupled to the system bus and configured to execute instruction words having a length of less than or equal to N;

a register file comprising a plurality of registers in a non-orthogonal arrangement with the low energy accelerator processor;

a first execution unit of the plurality of execution units configured to read data from and write data to each of the registers and execute a Fast Fourier Transform; and

a second execution unit of the plurality of execution units configured to read data from only a first number of the registers and write data to only a second number of the registers, wherein each of the first and second numbers is less than the plurality, and wherein the first number is less than the second number.

15. The data processor of claim 14 , comprising a third execution unit of the plurality of execution units configured to read data from only a third number of the registers and write data to only a fourth number of the registers, wherein each of the third and fourth numbers is less than the plurality, and wherein the third number is equal to the fourth number.

16. The data processor of claim 14 , wherein the first execution unit is a butterfly/adder ALU unit configured to execute the Fast Fourier Transform or Finite Impulse Response filtering in response to an instruction word.

17. The data processor of claim 14 , wherein the plurality of execution units comprises a load store execution unit, a load coefficient execution unit, a multiply execution unit, and a butterfly/adder ALU execution unit.

18. The data processor of claim 14 , wherein the register file is included with the low energy accelerator processor and directly accessed by only the plurality of execution units.

19. The data processor of claim 14 , wherein the low energy accelerator processor comprises a loop count register, a loop start register, and a loop end register configured to control a repetitive loop operation.

20. The data processor of claim 14 , wherein the low energy accelerator processor comprises a floating point flag register to indicate if at least one of the first and second execution units operates on floating point or fixed point data.