Method and apparatus for buffer chaining in a communications controller

In a system comprising a host computer, a communications controller and a data link connecting the communications controller to the host computer, wherein the communications controller includes a main memory, a channel adapter (CA) as the data interface to the data link, and a central control unit (CCU) for controlling the CA, a method of transmitting data between the host computer and the communications controller, said data including one or more individual delineated messages, and a plurality of buffers in the main memory for storing the data, wherein each of the buffers contains a next buffer pointer for forming a linked list and a next message pointer, said method comprising the steps of

• A) transmitting a data transfer request, including a pointer to the first buffer in a linked list, from the CCU to the CA,
• in response to the data transfer request at the CA,
• B) transferring data until the present buffer is exhausted or until an End-of-Message (EOM) signal is received,
• C) if an EOM signal has not been received, determining the next buffer pertaining to the present message and repeating step B),
• D) otherwise, determining if there is another message to be transferred,
• E) if there is another message to be transferred, determining from the next message pointer of one of the buffers of the last message the first buffer pertaining to the next message, and repeating steps B through D, and
• F) if there is no other message to be transferred, interrupting the CCU.