User guide

14-16

Negative Timing Checks

? ? ? * : ? : x ;

endtable

endprimitive

In this example, if you include the +neg_tchk compile-time option,

the $width timing check uses the delayed version of signal clk,

named d_clk, and the following sequence of events occurs:

1. At time 311 the delayed version of the clock transitions to 1,

causing output q to toggle to 1.

2. At time 312 the narrow pulse on the clock causes a width violation:

"test1.v", 31: Timing violation in top.dff1

$width( posedge clk:300, : 301, limit: 5);

The timing violation message looks like it occurs at time 301 but

you do not see it until time 312.

3. Also at time 312, reg notif toggles from X to 1. This changes

output q from 1 to X. There are no subsequent changes on output

Figure 14-2 Other Timing Checks Using the Delayed Versions