1-D SSR FFT Input Stream Reading and Writing Considerations - 2023.2 English

After synthesis, 1-D SSR FFT HLS IP maps to a processing block with stream interface at both the input and output.

If user requires a streaming 1-D SSR FFT block with FIFO interface at both the input and output, as shown in the following figure:

1. Declares the input and output streams explicitly with corresponding stream depth:

// input stream of innerFFT
hls::stream<I_TYPE, FIFO_DEPTH> inStrm[R];
// output stream of innerFFT
hls::stream<O_TYPE, FIFO_DEPTH> outStrm[R];

2. Feeds data to the input FIFO, or eats from the output one:

for (int t = 0; t < L / R; t++)
{
        for (int r = 0; r < R; r++)
        {
    inStrm[r].write(inD[r][t]);
        }
}

for (int t = 0; t < L / R; t++)
{
        for (int r = 0; r < R; r++)
        {
    outD[r][t] = outStrm[r].read();
        }
}

3. If the 1-D SSR FFT IP is facing another HLS IP in the input chain or output chain, the inner loop doing reading and writing should be unrolled.