( ESNUG 296 Item 7 ) ---------------------------------------------- [7/23/98]
From: Henry George Berkley <asic@netcom.com>
Subject: Chrono VCS Bug When Comparing Time & Integer Variables
Hi John,
When comparing time variables to negative integers, VCS gives erroneous
results. One of the busses on my ASIC has a negative hold requirement.
When writing a bus monitor to check this spec, I discovered the bug.
From bug1.v:
module bug1();
time Tvar;
initial begin
Tvar = 100;
if ( Tvar < -20 )
$display("We have a bug.");
end //initial
endmodule
From bug1.log:
Command: vcs -R bug1.v -l bug1.log
Chronologic Simulation VCS Release 4.1.1 Tue Jul 14 17:40:49 1998
Copyright Chronologic Simulation/Viewlogic '91-'96. All Rights Reserved.
This Licensed Software contains Confidential and proprietary information
which is the property of Chronologic Simulation
Compiling bug1.v
Top Level Modules:
bug1
1 unique modules to generate
1 of 1 modules done
Invoking loader...
Chronologic VCS simulator copyright 1991-1997
Contains Viewlogic proprietary information.
Compiler version 4.1.1; Runtime version 4.1.1; Jul 14 17:40 1998
We have a bug.
V C S S i m u l a t i o n R e p o r t
Time: 0
CPU Time: 0.067 seconds; Data structure size: 0.0Mb
Tue Jul 14 17:40:59 1998
My client is running VCS 4.1.1 on a Sparc running SunOS 4.1.4
The workaround is to use real numbers.
- Henry George Berkley
Electronic Consulting Santa Cruz, CA
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