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Subject: Constraint issue
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vbdc_montu
Posts: 6
Online: User is Offline
4/08/2008 1:34 PM  
Hi,
 
I’m trying to constraint two fields through a keep statement, but I’m receiving an error. This is the code:
 
struct packet{
...
    clkm: uint;
    keep soft clkm == 100;
 
    pkt_delay: uint;
    keep soft pkt_delay * 2 * clkm < 10000;
...
};
  
The error message:
  
      Previous constraints reduced its range of possible values,
        then the following constraint contradicted these values:
          keep pkt_delay * 2 * clkm < 100*  at line 79 in @packet
        Reduced: packet_s-@20.(pkt_delay*2*clkm) from Ύ..9999] into []
          Using: packet_s-@20.pkt_delay == �]
          Using: packet_s-@20.clkm == 𖏜]
 
It seems that the last keep is ignored when attributing value to fields clkm and pkt_delay; I tried without the “soft” in the keep statements but received the same error.
 
Thanks in advice
 
Montu

vbdc_montu
Posts: 6
Online: User is Offline
4/09/2008 12:30 PM  
My previous post is incorrect: when I use the code above I didn’t receive any errors, but the constraints seems to be ignored and a get values like 1270727026 for the pkt_delay field. I get the error above when I remove the soft constraints

Thanks for any suggestion
thinkverification
Posts: 28
Online: User is Offline
4/09/2008 12:35 PM  
if you're using PGEN (rather than IntelliGen) please try this:

keep soft pkt_delay == calc_pkt_delay();

calc_pkt_delay(): uint is {
gen result keeping {
it < 10000 / (2 * clkm);
};
};


Yaron
Yaron Ilani
VLSI Verification Specialist
www.ThinkVerification.com
vbdc_montu
Posts: 6
Online: User is Offline
4/10/2008 12:25 PM  
Hi Yaron, I’m using IntelliGen. But I tried:



keep pkt_delay < 10000 / 10000 / (2 * clkm);



, as you suggested inside your method and it worked (and I get surprised because I think I have tried this before and still get the error...).



Anyway, it worked!



Thank you!
thinkverification
Posts: 28
Online: User is Offline
4/10/2008 9:44 PM  
Great! Glad I could help.
Yaron Ilani
VLSI Verification Specialist
www.ThinkVerification.com
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Forums > Functional Verification > e > Constraint issue


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