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Voyager
Voyager
3,060 Views
Registered: ‎05-30-2017

LOC XST constraint with wildcard

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Hello,

I'm currently working on a design with Spartan 6 xc6slx150t-3fgg900, using ISE 14.7 and Verilog language. It is correct to write in a .v a constraint with the wildcard for example ( *LOC = "ILOGIC_X*Y*) or the wildcard can be used only in the .ufc? Thank you.

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Guide avrumw
Guide
5,347 Views
Registered: ‎01-23-2009

Re: LOC XST constraint with wildcard

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So, yes, it appears to be legal syntax, although I have never seen anyone use it.

 

Nonetheless, the "correct" way to force a flip-flop into the IOB is using the IOB property I described, not a LOC constraint with a wildcard.

 

Avrum

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Guide avrumw
Guide
3,048 Views
Registered: ‎01-23-2009

Re: LOC XST constraint with wildcard

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No. You cannot do this. It is not even legal in the UCF file; the LOC location must be a string with no wildcards.

 

If you want to force a flip-flop into the IOB (which is what the ILOGIC is), set the IOB=TRUE (or IOB=FORCE) property on the flip-flop. This CAN be done in the RTL.

 

(* IOB = "FORCE") reg my_iob_ff;

 

always @(posedge clk)

begin

  my_iob_ff <= (whatever);

end

 

This will force the flip-flop my_iob_ff into the IOB.

 

Avrum

Voyager
Voyager
2,960 Views
Registered: ‎05-30-2017

Re: LOC XST constraint with wildcard

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@avrumw,

thank you for the reply. Looking at https://www.xilinx.com/support/documentation/sw_manuals/xilinx11/cgd.pdf pg 124 it seem that using wildcards in LOCATION constraints in the .ucf file it is legal. What do you think? Thank you.

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Guide avrumw
Guide
5,348 Views
Registered: ‎01-23-2009

Re: LOC XST constraint with wildcard

Jump to solution

So, yes, it appears to be legal syntax, although I have never seen anyone use it.

 

Nonetheless, the "correct" way to force a flip-flop into the IOB is using the IOB property I described, not a LOC constraint with a wildcard.

 

Avrum

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Voyager
Voyager
2,908 Views
Registered: ‎05-30-2017

Re: LOC XST constraint with wildcard

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Thank you for the reply. I used the LOC constraint with wildcard because I wanted to force FFs and latches specifically in ILOGIC blocks. Thanks for the help!

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