Encore SIM EDITOR SOFTWARE Guide de l'utilisateur télécharger pdf (Page 75)

2-7

Modeling Your Design

Time Zero Race Conditions

The following race condition is subtle but very common:

always @(posedge clock)

$display("May or may not display");

initial begin

clock = 1;

forever #50 clock = ~clock;

end

This is a race condition because the transition of clock to 1 (posedge)

may happen before or after the event trigger (always @(posedge

clock)) is established. Often the race is not evident in the simulation

result because reset occurs at time zero.

The solution to this race condition is to guarantee that no transitions

take place at time zero of any signals inside event triggers. Rewrite

the clock driver in the above example as follows:

initial begin

clock = 1’bx;

#50 clock = 1’b0;

forever #50 clock = ~clock;

end

1 2 ... 70 71 72 73 74 75 76 77 78 79 80 ... 148 149

Pas de commentaire

Encore SIM EDITOR SOFTWARE Guide de l'utilisateur Page 75