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Voyager
Voyager
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Registered: ‎05-30-2017

Is there a constraint that allow to specify a resource that I don't want to use?

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Hello,

is there a constraint that allow to specify a resource that I don't want to use? For example don't use a BUFGMUX for a clock signal. Better if XST constraint .Thank you.

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Xilinx Employee
Xilinx Employee
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Registered: ‎05-14-2008

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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No, there is not a general constraint for you to prohibit any kind of macro inference.

 

Vivian

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Moderator
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Registered: ‎07-21-2014

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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@pierlum

 

There are two ways to control tool behaviour: 1. Use global XST settings. 2. Use attributes for the specific signals.

For example, use of -bufg '0' will make sure that XST generated netlist will not have any global clock buffers. Yes, this may not be an accepted solution of the problem as the other part of the design will need global clock buffers.

 

Use of attributes should help here, use buffer_type attribute and mentioned the preferred buffer for any particular signal declared in the design.

 

Thanks,
Anusheel
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Xilinx Employee
Xilinx Employee
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Registered: ‎05-14-2008

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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It depends.

For example, if you don't want XST to automatically insert BUFG for a clock signal, you can add "buffer_type" attribute to this signal.

Similar attributes like ram_style, rom_style, fsm_style, shreg_extract, use_dsp48 and etc.

 

BTW, XST won't automatically infer BUFGMUX for clock(s). BUFGMUX must be instantiated.

 

Vivian

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Voyager
Voyager
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Registered: ‎05-30-2017

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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Thank you @viviany and @anusheel for the help! Irrespective of the bufg, it exist a generic specific constrain to avoid the inferring of a specific macro of which I specify the name? Thank you.

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Xilinx Employee
Xilinx Employee
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Registered: ‎05-14-2008

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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No, there is not a general constraint for you to prohibit any kind of macro inference.

 

Vivian

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Voyager
Voyager
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Registered: ‎05-30-2017

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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Thanks for the help!

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Voyager
Voyager
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Registered: ‎05-30-2017

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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@viviany 

I work with ise 14.7 and spartan 6 and XST automatically uses BUFGMUX inferring them as BUFG.

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Voyager
Voyager
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Re: Is there a constraint that allow to specify a resource that I don't want to use?

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Sorry for the OT @viviany and @anusheel but someone of you could help me with the very strange problem that I explain here?https://forums.xilinx.com/t5/Implementation/LDCE-and-ILOGIC2-very-strange-problem/td-p/770728

I work with spartan 6 and ise 14.7. Thank you.

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Xilinx Employee
Xilinx Employee
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Registered: ‎05-14-2008

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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@pierlum wrote:

@viviany 

I work with ise 14.7 and spartan 6 and XST automatically uses BUFGMUX inferring them as BUFG.


BUFGMUX function must be instantiated. It accepts two clock input and does a 2-to-1 selection.

Are you sure you see a BUFGMUX inference? 

I guess it is just a BUFG. And BUFG is one of the configurations of BUFGCTRL.

BUFGMUX is another configuration of BUFGCTRL.

They are all based on BUFGCTRL primitive.

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Voyager
Voyager
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Registered: ‎05-30-2017

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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@viviany Sorry I explained wrong. The inferred macro it's a BUFG but from the point of view of the resources used infer BUFGs consume BUFGMUXs

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Guide
Guide
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Registered: ‎01-23-2009

Re: Is there a constraint that allow to specify a resource that I don't want to use?

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The Spartan-6 has only one type of global clock buffer - it is the BUFGMUX. A BUFG doesn't really exist - it is just a BUFGMUX with the S input tied to a constant (and one of the clock inputs ignored).

 

So the fact that it is using a BUFGMUX when you want a BUFG is correct. You can't (and don't want to) prevent this.

 

Avrum

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