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Honored Contributor I

Wide MACCs in Stratix III

I'm trying to build a 24-bit accumulator in Stratix III. I don't actually need a multiply function, but I'm using the DSP block anyway to be assured of fast operation. So, I'm taking my 24-bit value, and multiplying it by either 1 or -1 to add or subtract from the running total. 


The problem is, I cannot get any DSP Block-based accumulator wider than 18 bits to synthesize. I always get the following error message: 


Error: Can't elaborate user hierarchy "altmult_add:altmult_add_component" 


I've tried a number of different approaches, from the straightforward attack of asking the Megawizard generator to build a 24-bit MACC, to various sneaky approaches where I break the 24-bit number into two chunks, and feed it into two separate multipliers, each feeding the same accumulator. No dice. 


Any ideas? 




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