Problem simulating FFT IP core

[marnixFPGA]

Hi all,

I am trying to simulate the FFT IP core using cocotb.

I have the FFT setup as a 128 point, variable streaming, fixed point FFT with 12 bit natural input and 20 bit bit-reverse output.

I have successfully exported the IP core from quartus megawizard, compiled it using Questasim, and linked it without any issues. I have followed the instructions about input flow control, and I believe I am controlling the values of sink_sop, sink_valid, etc. correctly. 

However, when I run the simulation, it keeps crashing with an underflow error. 

# ** Fatal: (vsim-3421) Value -1 is out of range 0 to 7.
# Time: 570 ns Iteration: 2 Process: /fft_ip_0430/fft_ii_0/auk_dspip_r22sdf_top_inst/r22sdf_core_inst/gen_natural_order_core/gen_stages(3)/r22_stage/processing_cnt_p File: C:/intelFPGA_lite/23.1std/quartus/libraries/custom/fft_ip_0430/fft_ip_0430/simulation/submodules/mentor/auk_dspip_r22sdf_stage.vhd Line: 1002
# Fatal error in Process processing_cnt_p at C:/intelFPGA_lite/23.1std/quartus/libraries/custom/fft_ip_0430/fft_ip_0430/simulation/submodules/mentor/auk_dspip_r22sdf_stage.vhd line 1002

I've attached the fft toplevel, python testbench, Makefile and the waveform file of the simulation in 'simfiles_20240105.zip' to this post for more detailed insights. I am wondering if anyone here has experience with simulating the FFT IP core and might be able to suggest what could be causing this error or how to resolve it. Any tips or advice would be greatly appreciated!

Thanks in advance for your help!

Marnix

[Kshitij_Intel]

Hi,

I would suggest keep your inputs synchronous with input valid in your testbench. Until valid is high send input data as zeros.

Also, try simulating the FFT IP independently in Questasim or any other simulation tool.

Hope this help.

Thank you,

Kshitij Goel

[Kshitij_Intel]

Hi,

As we do not receive any response from you on the previous answer that we have provided. Please login to ‘https://supporttickets.intel.com’, view details of the desire request, and post a response within the next 15 days to allow me to continue to support you. After 15 days, this thread will be transitioned to community support. The community users will be able to help you on your follow-up questions.

Thank you,

Kshitij Goel