FFT IP Core: User Guide

ID 683374
Date 11/06/2017
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3.4.3.1. Enabling the Buffered Burst FFT

Figure 17. FFT Buffered Burst Data Flow Input Flow Control
  1. Following the interval of time where the FFT processor reads the input samples from an internal input buffer, it re-asserts sink_ready indicating it is ready to read in the next input block. Apply a pulse on sink_sop aligned in time with the first input sample of the next block to indicate the beginning of the subsequent input block.
  2. As in all data flows, the logical level of inverse for a particular block is registered by the FFT at the time when you assert the start-of-packet signal, sink_sop.

When the FFT completes the transform of the input block, it asserts the source_valid and outputs the complex transform domain data block in natural order .

Figure 18. FFT Buffered Burst Data Flow Output Flow Control

Signals source_sop and source_eop indicate the start-of-packet and end-of-packet for the output block data respectively.

Note: You must assert the sink_valid signal for source_valid to be asserted (and a valid data output). You must leave sink_valid signal asserted at the end of data transfers to extract the final frames of data from the FFT.
  1. Deassert the system reset.
  2. Asserts sink_valid to indicate to the FFT function that valid data is available for input. A successful data transfer occurs when both the sink_valid and the sink_ready are asserted.
  3. Load the first complex data sample into the FFT function and simultaneously asserts sink_sop to indicate the start of the input block.
  4. On the next clock cycle, sink_sop is deasserted and you must load the following N – 1 complex input data samples in natural order.
  5. On the last complex data sample, assert sink_eop.
  6. When you load the input block, the FFT function begins computing the transform on the stored input block. Hold the sink_ready signal high as you can transfer the first few samples of the subsequent frame into the small FIFO at the input. If this FIFO buffer is filled, the FFT deasserts the sink_ready signal. It is not mandatory to transfer samples during sink_ready cycles.

FFT Buffered Burst Data Flow Simulation Waveform