I am using LPM mult IP for 9x9 multiplication on cyclone V GT device. I had set the latency as 3. So each DSP used to provide me 3 9x9 multipliers. So totally there would be 315 DSPs(3 * 315 - 9x9 multipliers). Since my design is tight on resources, I tried reducing the latency to 1. In this case, the fitter always uses 18x18 multipliers, hence my dsp utilization is going up and I am getting error as "no legal placement for multipliers".
Does latency affect the usage of 9x9 multipliers?
IS there way i can make the dsp use only 9x9 while using latency as 1?
I have attached the dsp usage summary for latency 1.
Each of the DSP block is able to fit 3 independent 9x9 multiplier. The DSP merging will automatically kicks in when there are not enough DSPs in the region of interest. The output latency setting is not supposed to impact this. From my side, no matter it is 1 or 3 clock cycles, from the Fitter -> DSP Block Usage Summary Report, it show independent 9x9 multiplier. I believe this could be something else caused the fitter error since there are many DSP configuration based on the attached file. You may starting to debug it by simplify the design with only independent 9x9 multiplier.
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