Sent to a media driver to request a real-time delay on output. The data buffer associated with this message is expected to contain an integer to indicate the number of machine cycles of delay desired. M_DELAY messages are typically used to prevent transmitted data from exceeding the buffering capacity of slower terminals.
The message format is not defined by STREAMS and its use is developer dependent. Not all media drivers may understand this message. This message may be considered a special case of an M_CTL message. An M_DELAY message cannot be generated by a user-level process and is always discarded if passed to the stream head.