Pipelined drivers: Take the example of AHB… At each clock there are multiple things are going on , the HADDR signal holds the address of the current transaction, the HWDATA holds the data from the previous transaction and HRESP may hold the response of an even earlier transaction.
If you are building this driver, you will have to manage the pipeline of transactions carefully in the driver so that you can drive different parts of these pipelined transactions onto the AHB interface.