Hi
I'm having problems with DSP in my design. I've implemented a large (27 DSP, just the multipliers) combinational block that performs some math's and it works great (with no clk) both in behavioral and post PAR simulations. The problem arise when I try to add some FF to the design (e.g. to feedback the output), in this case the behavioral simulation goes fine but the post PAR doesn't. The combinational block has a different output for the same input.
If now I test the system with the option dsp_utilization_ratio in 0, then everything goes fine in post PAR. So I think the problem is in the inability of XST to manage both a large number of DSP and a large number of FF at the same time. I can't figure out how is posible that the comb system works in a different way in post PAR simulation , I try with the issue named here: http://www.xilinx.com/support/answers/22314.htm because looks very similar but I've got nothing.
There are no warnings in the whole process. And the clk I use when I add the FF is enough for the comb system to work properly.
I'm working with ISE 12.4 , Isim and the bigest spartan 6
Which kind of implementation options can I use to deal with this problem ?
Thanks !!
