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weberrm
Posts: 0
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5/11/2006 5:21 AM
Using the example below, how can I override the constraints of classes A and B on an instance by instance basis? For instance, let's say I wanted a1's constraint of VarA0 to be VarA0 > 3 and b1's constraint of VarB1 to be VarB1 < 5. The point being that in general I want to use the default constraints provided by the class, but for some instances I want to override them. Thanks! module test(); class A; rand bit Α:0] varA0; rand bit Α:0] varA1; constraint c0 { varA0 > 1; } constraint c1 { varA1 > 2; } endclass class B; rand bit Α:0] varB0; rand bit Α:0] varB1; constraint c0 { varB0 > 1; } constraint c1 { varB1 > 2; } endclass A a0=new; A a1=new; B b0=new; B b1=new; initial begin if (a0.randomize()==0) begin $display("error!"); end if (a1.randomize()==0) begin $display("error!"); end if (b0.randomize()==0) begin $display("error!"); end if (b1.randomize()==0) begin $display("error!"); end $display("a0.varA0=%d",a0.varA0); $display("a0.varA1=%d",a0.varA1); $display("a1.varA0=%d",a1.varA0); $display("a1.varA1=%d",a1.varA1); $display("b0.varB0=%d",b0.varB0); $display("b0.varB1=%d",b0.varB1); $display("b1.varB0=%d",b1.varB0); $display("b1.varB1=%d",b1.varB1); end endmodule

kameade
Posts: 13
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5/11/2006 10:30 AM
Hello! There are quite a few different ways to change constraints for a specific instance of the class. The easiest way to do it is to use the b1.randomize() with {constraint} notation. if (a1.randomize() with { varA0 > 3;}) $display("a1.varA0=%d a1.varA1=%d", a1.varA0, a1.varA1) else $display("a1.randomize error"); if (b1.randomize() with {varB1 <5;}) $display("b1.varB0=%d b1.varB1=%d", b1.varB0, b1.varB1); else $display("b1.randomize error"); The with {...} would have to be used each time you invoke randomize for that instance though. Other options are to use external constraint blocks - but those are class-specific. Or you can extend a class and only modify the constraints (overwrite a constraint or add an additional constraint). You also have the option to enable and disable constraints using the constraint_mode() methods. I hope that helps a little.... Kathleen Meade (meade@cadence.com)

tpylant
Posts: 87
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9/20/2006 10:07 AM
Attached is a presentation I created for random data generation which includes slides on overriding constraints. Tim
Attachment: generation.pdf

parag123
Posts: 2
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4/03/2007 9:39 PM
Hello Tim, I am a new user for SV & while going thru the forum I found that u have attached a pdf, but that seems to be encrypted and I am unable to open it. Same is the case with "itp_pylant_generation.pdf" posted onto the forum. Is there any special way to open it. Could u plz help me out. Parag parag@txc.stpn.soft.net

Akiva
Moderator
Posts: 6
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4/02/2008 6:30 PM
Hi, I have written a brief article on soft constraints: http://www.aceverification.com/Soft%20Constraints%20for%20SystemVerilog.pdf Also, you can download Ace Verification's soft constraints for SV at the following link: http://www.aceverification.com/softconstraints_pkg.htm Akiva

Akiva
Moderator
Posts: 6
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4/02/2008 6:30 PM
Hi, I have written a brief article on soft constraints: http://www.aceverification.com/Soft%20Constraints%20for%20SystemVerilog.pdf Also, you can download Ace Verification's soft constraints for SV at the following link: http://www.aceverification.com/softconstraints_pkg.htm Akiva

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