A device interface for communicating between a processor system and a separate device employs cacheable control registers, both to indicate the receipt of a message and to receive messages to be transmitted. The data structure of the cacheable control registers may be that of a queue, minimizing the need for routine handshaking signals to clear the queue after each message. Communication of queue pointers is minimized by the use of a shadow pointer relied on as long as adequate queue space exists and queue entry valid flags which are interpreted with alternate sense for each cycling through the queue.