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gallopr
Newbie
Joined: Nov 10, 2004
Posts: 1
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 Posted: Wed Nov 10, 2004 7:58 am Post subject: PSL Newbie question |
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Am trying to write a property to check the value out of a register is not x the cycle after a readspecifer is non zero. This is just like some simple examples I have but involves buses and comparisons which I think are what is catching me out.
I currently have:
| Code: | | property RegReadPortNotX = never ((readspec[5:0] !== 6'h0) -> next ((^(out0[31:0])) === 1'bx)); |
but I get an error compiling with ncvlog:
| Code: | | Illegal context for a Sugar formula. |
at the -> operator.
Any ideas?
Thanks
Russ |
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vhdlcohen
Industry Expert
Joined: Jan 05, 2004
Posts: 1239
Location: Los Angeles, CA
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| Posted: Wed Nov 10, 2004 9:40 am Post subject: |
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| Quote: | | property RegReadPortNotX = never ((readspec[5:0] !== 6'h0) -> next ((^(out0[31:0])) === 1'bx)); |
You should never use a "never" with an implication operator because it will yiled errors. and many compilers now forbid it. Specifically,
never (a -> b) says that the property a-> b should always be FALSE.
The never of false is true. But if "a" is zero or false, then a -> b is vacuously TRUE,
Change you code to:
| Code: | | property RegReadPortNotX = never {readspec[5:0] !== 6'h0 ; ^(out0[31:0]) === 1'bx}; |
I am not sure about your comparison of a 32 bit vector to a 1 bit though!
But the concept is to use "never {sequence}" instead of the implication.
Ben Cohen
_________________
Ben Cohen http://www.systemverilog.us/
* SystemVerilog Assertions Handbook, 3rd Edition, 2013
* A Pragmatic Approach to VMM Adoption
* Using PSL/SUGAR ... 2nd Edition
* Real Chip Design and Verification
* Cmpt Design by Example
* VHDL books |
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hemanth
Senior
Joined: Aug 16, 2004
Posts: 93
Location: Bangalore
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| Posted: Mon Nov 15, 2004 2:26 am Post subject: |
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I think you can convert that NEVER to an equivalent ALWAYS and write something like-
property RegReadPortNotX = always((readspec[5:0] !== 6'h0) -> next(^(out0[31:0]) !== 1'bx)); |
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vhdlcohen
Industry Expert
Joined: Jan 05, 2004
Posts: 1239
Location: Los Angeles, CA
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| Posted: Mon Nov 15, 2004 11:36 am Post subject: |
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| Quote: | I think you can convert that NEVER to an equivalent ALWAYS and write something like-
property RegReadPortNotX = always((readspec[5:0] !== 6'h0) -> next(^(out0[31:0]) !== 1'bx)); |
In the general case, to state that:
if(A) then never B at next cycle, and
if(!A) then vacuously true
you can write one of the followings:
never {A ; B} // never of a sequence
always {A} |=> {!B} // I prefer sequences
always {A} |=> {B} |-> {false}
This last case is valid because a property is defined as:
FL_Property ::= // among other things
Sequence [ ! ]
| Sequence |-> FL_Property
| Sequence |=> FL_Property
and thru recursion, you get:
FL_Property ::=
Sequence |=> Sequence |-> FL_Property
A tool supports that fully supports PSL should support this.
Ben Cohen
_________________
Ben Cohen http://www.systemverilog.us/
* SystemVerilog Assertions Handbook, 3rd Edition, 2013
* A Pragmatic Approach to VMM Adoption
* Using PSL/SUGAR ... 2nd Edition
* Real Chip Design and Verification
* Cmpt Design by Example
* VHDL books |
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