Encore SIM EDITOR SOFTWARE Guida Utente Scaricare il pdf (Pagina 123)

3-15

Compiling and Elaborating Your Design

VCS displays this warning every time it evaluates the conditional

expression to have an X or Z value, not just when the signal or signals

in the expression transition to an X or Z value.

VCS does not display a warning message when a sub-expression

has the value X or Z, but the conditional expression evaluates to a 1

or 0 value. For example:

r1 = 1’bz;

r2 = 1’b1;

if ( (r1 && r2 ) || 1’b1)

r3 = 1;

In this example the conditional expression always evaluates to a 1

value so VCS does not display a warning message.

Enabling the Checking

The -xzcheck compile-time option checks all the conditional

expressions in the design and displays a warning message every

time it evaluates a conditional expression to have an X or Z value.

You can suppress or enable these warning messages globally or on

selected modules using $xzcheckoff and $xzcheckon system

tasks. For more details on $xzcheckoff and $xzcheckon system

tasks, see “Checking for X and Z Values in Conditional Expressions”

on page D-41

The -xzcheck compile-time option has an optional argument to

suppress the warning for glitches evaluating to X or Z value. Synopsys

calls these glitches as false negatives. See “Filtering Out False

Negatives” on page 3-16.

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Encore SIM EDITOR SOFTWARE Guida Utente Pagina 123