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Registered: ‎02-20-2019

Synthesis hangs in HLS 2019.2.1 on SSR FFT example

Hi Folks,

I've managed to get the basic SSR FFT example here working in HLS by running the attached, modified version of the 1dfix_impluse/run_hls.tcl script. Before it would synthesize I had to fix 4 bugs in hls_ssr_fft_parallel_fft_kernel.hpp:

  • Deleted lines 130 and 695 which had pragmas for undeclared variables (#pragma HLS ARRAY_PARTITION variable = D2t complete dim = 1)
  • Changed local_r8_twiddle_table to local_r16_twiddle_table on lines 307 and 856 (#pragma HLS ARRAY_PARTITION variable = local_r8_twiddle_table complete dim = 1).

With these changes the project will successfully synthesize. Unfortunately I need a 4096 point FFT with an SSR of 16. When I attempt to synthesize this things proceed as before until HLS starts to pipeline loop 'L_BFLYs_LOOP' while implementing module 'fftStageKernelS2S'. Here HLS stalls, CPU usage falls to 0% and RAM idles at a few GB. I'm on an 8 core i9 with 64GB of RAM. As an aside the hang also occurs with a 1024x16 fft, so I'm guessing it is a bug in the 16x SSR templates.

My guess is a pragma issue in the headers but without any error messages I don't have a clue.

Here is a direct link to what is probably the most up-to-date documentation at the time of this post.

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