An HDLC formatter and a message processing core exchange messages over a high speed message exchange interface. The interface includes a memory shared by the HDLC formatter and the message processing core. A handshaking arrangement is used to coordinate message storage and retrieval in the shared memory by the HDLC formatter and the message processing core with minimal utilization of processing resources of the message processing core. This handshaking coordination, together with the use of a message buffer accessed by the HDLC formatter to buffer channelized messages exchanged with the message processing core, facilitates message processing on multiple serial links (e.g., 3) over multiple timeslots (e.g., 256).