Is there any DSP56000 software available that shows how to use a
256-point complex FFT made up of 512 real points, i.e., what is the
best way to pack the array on the input side to be able to combine
the unpacking with the last pass of the FFT?

Three ways of using complex FFTs to transform real data are described in
a recenly published article:  "Real-Valued Fast Fourier Transform Algorithms"
by H. Sorensen, D. Jones, M. Heideman, and C. Burrus in IEEE Transactions on
Acoustics, Speech and Digital Processing, Vol. ASSP-35, #6, June 1987, 
pp 849-863.  They involve preprocessing the real data to make it appear
complex prior to input to the complex FFT and postprocessing the complex
output to build the real output.  We currently have three complex FFT
algorithms (listed on Dr. BuB as free DSP56000/1 general purpose FFT
software) that could be used for your 512-point real FFT--FFTR2A, FFTR2B,
and FFTR2C.


