what is deifferent of delay_mode_zero and delay_mode_unit?

[atuo]

delay_mode_zero

When I simulate netlist without sdf using VCS.I use the +delay_mode_zero compile time option, the simulation result is error. But using the +delay_mode_unit ,the simulation result is right. I don't know why?

Thanks.

 

[vamsid]

delay_mode_unit

delay_mode_zero specifies zero delay where as delay_mode_unit specifies one unit (depending on the specified timescale) delay. So there are chances of difference in simulation behaviors between these two options.

Eg:

assign #5 a = b;

with delay_mode_zero the delay will be 0. Assuming timescale is 1ps/1ps, then with delay_mode_unit the delay will be 1 ps.

Added after 17 minutes:

to be more specific to netlist without sdf, delay_mode_unit will add a unit delay on all the output ports whereas the delay_mode_zero will not. So there are chances that the simulation results are different.