Это не тот бэкдор скорей всего :)
The backdoor is a technique to directly put/get the value onto the register variable in the design RTL signal, for which you have to build up the hierarchical path to the registers. Backdoor does not consume any simulation time, and is faster. But it is quite insufficient to be the only mode of verification. This is usually done during the early testbench development phase or when agents that can drive transactions to the DUT are not available.