The 4 operating modes of the FFT

Burst FFT: The burst FFT process one frame of data at a time. The core needs to finish processing and outputting that one frame of data before it can accept more inputs.

Buffered burst FFT: The buffered burst FFT takes a couple frames of data at a time. The core would need to finish processing those couple frame of data before it can accept more inputs.

Note: Buffered burst, burst and streaming FFT all use Block Floating Point algorithm.

Variable Streaming FFT: This is a streaming FFT. However, you can run-time configure the FFT size if you want. For example, if I have a 1024 point VS FFT, then I can change the FFT size on the fly (anywhere up to 1024 points). The change would apply to the subsequent packet.

Note: Variable streaming uses a radix 2^2 structure and it support fixed point (allows for natural bit growth) and floating point (IEEE 754 single point precision).

Also I recommend using the 8.0 version of FFT. Due to the interaction between the built in Avalon ST FIFO and the FFT core, the burst and buffered burst modes don't really behave correctly. (Take burst for example, rather than taking one frame of data, then core would have to take one frame + the next couple samples from the subsequent frame, before it would start computing). I heard that problem has been fixed in the 8.0 release...

I will post some examples later if I can find them on my machine...

Hope this helps...

of course, you can use use VS to simulate the other modes (by controlling the sink_valid signal)...

Here is a sample design that I built... using VS FFT to simulate a bursty FFT... (also includes a Verilog state machine to control the FFT)...

Version: 7.2

Hello!

Wronghorizon, I was going through some of your code for the FFT control to familiarize myself with what's needed. I was able to understand the code except for one parameter, PULSE_BW_FM. What is it used for?

Thanks!

fpga_beginner

Thanks wronghorizon!

I actually figured it out what the variable was using waveform testing - I noticed the delay in inputting data to the engine.

Appreciate the reply