difference between freeze, deposit and drive

[gck]

freeze drive deposit

I am working on Modelsim. whenever we need to assigne value to signal we have three choices freeze, deposit and drive. Can anybody explain what exactly is the difference between them?

which one should be used in what condition.

Thank you

 

[avimit]

deposit: it will put a value to a signal, but it will hold until it is overwritten.
for example if I 'deposite' a Q of a flip flop to a '0', it will remain a '0', untill the simulation updates it to a new value. It is like giving a initial value to a signal.
freeze: it will put a value to a signal, and this value will remain as such throughout the simulaiton. It cannot be overwritten by simulation.
drive: it will upt a value to a signal, and if it is updated by simulation, it will then 'resolve' to a new value. Say if you dirve a signal to '1', and simulaion value is '0', then the signal will go 'X'
Hope it helps
Kr,
Avi