Is there delta=0 except at the beginning moment?

[fl]

Hi,
I find that only at the simulation beginning that delta =0. Other time
it is at least +1, or larger. I want to know that it is possible that
delta=0 in the middle of simulation?

Thanks.

 

[Alan Fitch]

On 11/09/11 15:24, fl wrote:

Hi,
I find that only at the simulation beginning that delta =0. Other time
it is at least +1, or larger. I want to know that it is possible that
delta=0 in the middle of simulation?

Thanks.

What do mean by "in the middle of the simulation"? If you set a break
point, or single step the code, you can see delta=0.

regards
Alan

P.S. Or write a simulation where time doesn't advance

--
Alan Fitch

 

[Paul Uiterlinden]

fl wrote:

Hi,
I find that only at the simulation beginning that delta =0. Other time
it is at least +1, or larger. I want to know that it is possible that
delta=0 in the middle of simulation?

A late reply.

I suppose you only see deltas larger than zero because you put break points
in synthesisable code. In general, these are processes that wake up on
signal events. Primary input signals generated in a testbench (such as a
clock) usually change at times with a delta=1. Other signals after that, so
delta >= 2.

Take for example a clock generator:

clk_gen: clk <= NOT clk AFTER half_clk_period;

Or:

clk_gen: PROCESS IS
BEGIN
WAIT for half_clk_period;
clk <= NOT clk;
END PROCESS clk_gen;

Put a break point on the line "clk <= NOT clk;" in the process and you'll
see times that are multiples of half_clk_period, all with delta=0.

--
Paul Uiterlinden
www.aimvalley.nl
e-mail addres: remove the not.