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Once you know what the path goes through, you can either change the code so it doesn't exist or do a set_false_path assignment to tell TimeQuest not to analyze it.
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I have tried :
1. analyze the path and found a large ripple carry path and ignored it for the wrong reason
2. to set a max delay for the path. This did not help.
3. to change the code by adding additional pipelining registers to the control path. It did not help.
Coming back to point 1. I ignored this one cause I tought that the used Carry look ahead adder (with 196 LE's)
was not so dramatic in size as the LPM_ADD_SUB (96 LE's)
Well in timing it does matter. The LE's for the LPM_ADD_SUB are put in arithmetic mode and implements a Full Adder.
I have gone from -15 ns slack to +2.5 ns.
best regards
Simon
Honored Contributor
