Methods and apparatus for twiddle factor generation for use with a programmable mixed-radix DFT/IDFT processor
Twiddle factor generation for use with a programmable mix-radix vector processor (“PVP”) capable of calculating discrete Fourier transform (“DFT/IDFT”) values. In an exemplary embodiment, an apparatus includes look-up table logic that receives twiddle control factors and outputs a selected twiddle factor scaler value (TFSV), a base vector generator that generates a base vector values based on the selected TFSV, and a twiddle column generator that generates a twiddle vector from the base vector.
1. A device containing a programmable vector processor (PVP) able to process data for network communication, comprising:
a state machine configured to generate twiddle factor control (TFC) signals, scaling control signals, and radix engine control signals;
a twiddle factor generator coupled to the state machine and able to provide twiddle factor data in accordance with the TFC signals;
a scaling unit coupled to the state machine and operable to scale pipeline vector data based on the scaling control signals; and
a mixed radix engine coupled to the state machine and configured to generate a first radix result via radix factorization in response to the radix engine control signals.
2. The device of claim 1 , wherein the mixed radix engine is configured to perform iteration in accordance with the radix engine control signals by calculating a second radix result in response to the first radix result.
3. The device of claim 1 , wherein the mixed radix engine is programmed to facilitate generation of a discrete Fourier transform (DFT) output in response to the first radix result.
4. The device of claim 1 , wherein the mixed radix engine is programmed to facilitate generation of an inverse discrete Fourier transform (IDFT) output in response to the first radix result.
5. The device of claim 1 , further comprising a look-up table (LUT) coupled to twiddle factor generator and configured to store a set of radix twiddle coefficients and configured to receive twiddle control factors.
6. The device of claim 5 , wherein the LUT facilitates to output a selected twiddle factor scaler value (TFSV) in accordance with the twiddle control factors and one or more radix twiddle coefficients.
7. The device of claim 6 , further comprising a base vector generator coupled to the LUT and configured to generate a base vector value in accordance with the selected TFSV.
8. The device of claim 1 , wherein the LUT stores TFSVs for radix 3 and radix 6.
9. The device of claim 1 , wherein the LUT is configured to store TFSVs for radix 4 and radix 5.
10. The device of claim 1 , wherein the twiddle vector generator includes a vector cross multiplier that iteratively multiplies the base vector to generate the twiddle vector.
11. The device of claim 10 , wherein the twiddle vector generator includes step coefficients to compute twiddle vectors for a last radix stage.
12. The device of claim 1 , wherein the twiddle vector is output to a twiddle multiplication unit in a vector pipeline that carries up to 12 samples per cycle.
13. A method of generating twiddle values for a programmable vector processor (PVP) for network communication, the method comprising:
providing twiddle factor control (TFC) signals by a state machine to a twiddle factor generator for generating twiddle factor data;
sending scaling control signals via the state machine to a scaling unit for scaling pipeline vector data;
forwarding radix engine control signals from the state machine to a mixed radix engine for computing an intermediate radix result in response to the twiddle factor data and the pipeline vector data; and
storing the intermediate radix result in a memory bank for next iteration for determining a discrete Fourier transform (DFT) result.
14. The method of claim 13 , further comprising receiving twiddle control factors, by look-up table (“LUT”) logic, containing information relating to twiddle factor.
15. The method of claim 13 , further comprising
searching an LUT to identify at least one radix twiddle coefficient in accordance with the twiddle control factors; and
obtaining a selected twiddle factor scaler value (TFSV) in response to the radix twiddle coefficient.
16. The method of claim 15 , further comprising generating a base vector value based on the TFSV and generating a twiddle vector from the base vector.
17. The method of claim 15 , further comprising generating an address associated with the received twiddle control factors.
18. A method of generating twiddle values via multiple iterations in a programmable vector processor (PVP), the method comprising:
forwarding vector data from a memory to a vector mixed-radix engine via a vector data-path pipeline;
computing by the vector mixed-radix engine an intermediate radix result in accordance with the vector data;
storing the intermediate radix result in the memory for next iteration;
reconfiguring the vector mixed-radix engine based on a next radix factor; and
outputting a final radix result by the vector mix-radix engine in response to the intermediate radix result retrieved from the memory passing through the vector data-path pipeline.
19. The method of claim 18 , wherein forwarding vector data from a memory to a vector mixed-radix engine further includes providing twiddle factor control (TFC) signals by a state machine to a twiddle factor generator for generating twiddle factor data.
20. The method of claim 18 , wherein forwarding vector data from a memory to a vector mixed-radix engine further includes sending scaling control signals via the state machine to a scaling unit for scaling pipeline vector data.