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Visitor
Visitor
942 Views
Registered: ‎12-21-2017

my 'Number of fully used LUT-FF pairs' is over 100%

Update:

 

I was implemented a FFT ip core 7.1 on v5-130t platform using ISE 14.7, and wrote a top module just to initialize this FFT ip core, and this top module actually didn't do anything except for some necessaries.

 

----------------------------original questions---------------------------------------------------------

After synthesis, the report said that my 'Number of fully used LUT-FF pairs' is 105%. Why does it happen? How can I solve it.

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Observer
Observer
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Registered: ‎01-08-2018

Re: my 'Number of fully used LUT-FF pairs' is over 100%

You are in trouble.

 

Sometimes, implementation happens to cut away some corners and fit but I'm not sure I would trust that.

 

Why does it happen? Your design is too complex. You most likely will have to do some (more or less) contrived rewriting. Reducing parallelism might work. You might also try move something to block ram if you're not using it. DSPs also have internal registers which can save 'true' flip-flops as far as I've understood. Most likely you'll get some performance reduction but your mileage will vary and anyway half performance is still better than none at all.

 

For a 5% maybe you can just check your FSM encoding and be in, difficult to say without details.

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Moderator
Moderator
880 Views
Registered: ‎03-16-2017

Re: my 'Number of fully used LUT-FF pairs' is over 100%

Hi @maxdz8,

 

What logic are you trying to implement?  You may have to modify your RTL to reduce the utilization of LUTs and FFs.

Try with Vivado default synthesis strategy and check the utilization. 

 

Share your synthesis log (runme.log) file from synth_1 directory to look into it.

 

Regards,

hemangd

Regards,
hemangd

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Moderator
Moderator
843 Views
Registered: ‎07-21-2014

Re: my 'Number of fully used LUT-FF pairs' is over 100%

@napoleonhoo

 

Try to check if some logic can be moved into BRAM/DSP blocks. For example, if there are any arrays/FSM which are not using BRAM.

 

Do you see any reduction after implementation?

 

Thanks

Anusheel

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