I'm looking for C code to do an FFT on a Cygnal C8051. Has anyone done this?
Try "Numerical Recipes in C" by William T. Vetterling. Softcover is about $40 and includes a diskette. Hope you have a high speed version of an 8051 to run on, because these algorithms are math intensive...
As stated, the "Numerical Recipes in C" is a good book and provides pseudo code and description of coding FFTs. However, unless the 51 processor you're using has an intrinsic floating point processor, your likely to get only SFTs (Slow Fourier Transforms) at best out of it :) Somebody should make a peripheral bus device that embedds FFT. Analog signal on the input, spectral result registers via parallel bus interface on the other side. Would be a handy little device to throw at any number of problems for an embedded ckt board.
Siemens (now Infineon) ApNote AP1634 "describes an implementation of a real-valued 1024 point decimation in time radix-2 FFT for the C166 microcontroller family. Assuming that the code is started out of the internal ROM via a 16-bit demultiplexed bus, an execution time of 10 ms has been achieved for a C165 running at 25 MHz internal clock. The code comprises 828 bytes." I think there might also be something on the Intel site http://developer.intel.com/design/mcs51/