The relevant functions are called and the return types and sizes verified. The API for the user is not implemented yet.
Now an arbitrary number of samples can be read and appended to the FFT block. Old samples will be dropped such that only BLOCK_LEN samples are in the memory buffer. Currently one half of the FFT block is replaced per update.
Start experimenting with Rust. This is a little experimental, but fully functional real-time FFT program based on the FFTW library.
Thomas Kolb