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03-31-2009, 10:10 PM
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XST removes duplicate logic no matter what
I've been fighting XST not to remove duplicate logic I put on purpose to
decrease fanout on some nets and I can't find a set of attributes, which would work... I tried "keep" and "noreduce" in combination with MAX_FANOUT, but XST(8.2.03i) seems to just ignore them all. Does anyone know how to force the damn thing to keep the duplicate logic? Thanks, /Mikhail 
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03-31-2009, 10:28 PM
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Re: XST removes duplicate logic no matter what
On Mar 31, 5:10*pm, "MM" <[email protected]> wrote:
> I've been fighting XST not to remove duplicate logic I put on purpose to > decrease fanout on some nets and I can't find a set of attributes, which > would work... I tried "keep" and "noreduce" in combination with MAX_FANOUT, > but XST(8.2.03i) seems to just ignore them all. Does anyone know how to > force the damn thing to keep the duplicate logic? > > Thanks, > /Mikhail If you run from the ISE GUI, set the following in the Xilinx-specific options tab of the Synthesis properties: Register Duplication: checked Equivalent Register Removal: unchecked Then in the HDL Options tab uncheck "Resource Sharing". This should allow XST to duplicate registers as necessary to reduce fanout as well as to push registers into IOBs if requested. Regards, Gabor
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03-31-2009, 10:31 PM
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Re: XST removes duplicate logic no matter what
MM wrote:
> I've been fighting XST not to remove duplicate logic I put on purpose to > decrease fanout on some nets There is a max_fanout constraint, but I would just constrain Fmax and let synthesis work out the details. -- Mike Treseler
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03-31-2009, 10:38 PM
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Re: XST removes duplicate logic no matter what
"Mike Treseler" <[email protected]> wrote in message
news:[email protected]... > > There is a max_fanout constraint, > but I would just constrain Fmax > and let synthesis work out the details. I am in the fine tuning mode. The design is big and I am trying to achieve closure on just a few last nets. /Mikhail
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03-31-2009, 10:53 PM
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Re: XST removes duplicate logic no matter what
"gabor" <[email protected]> wrote in message
news:[email protected]... >If you run from the ISE GUI, set the following in the Xilinx-specific >options tab of the Synthesis properties: > >Register Duplication: checked >Equivalent Register Removal: unchecked > >Then in the HDL Options tab uncheck "Resource Sharing". Thanks. Giving this a try. It must have been Equivalent Register Removal setting! I wish the tools would produce meaningful warnings about the user constraints been overridden! /Mikhail
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