In reply to Malai_21:
The adapter code is going to be invoked differently depending on how you have set up prediction. If you are using explicit prediction, both bus2reg() and reg2bus() will be called at some point but if you are using implicit prediction only bus2reg() will be called.
Explicit prediction is recommended (see VA articles on the register model to understand why but it has to do with flexibility & reuse). In that scenario, a read() call to a given register will utilize bus2reg() in order to convert the generic register access into a protocol-specific bus transaction which is issued via the associated sequencer/driver. When the actual operation is seen by the associated monitor component, it emits a transaction on its analysis port which is connected to the RAL, triggering a call to reg2bus() in order to figure out what happened and update the model.
If implicit prediction is used, the model update occurs in conjunction with the creation of the transaction on the sequencer/driver (the monitor is not needed in this setup) so only bus2reg() is used.