Mechanism for receiving messages at a coupling facility

A computer system mechanism, comprising:

• a coupling facility for providing a central data storage as well as a bidirectional control and data exchange pathway between a plurality of independent central processing units (CPUs) operating externally of said coupling facility,
• each one of said plurality of independent CPUs having a main memory, an operating system, and a communications interface form communicating with the coupling facility via an intersystem channel,
• said coupling facility including within said coupling facility, a plurality of separate coupling facility processors, a plurality of intersystem channels, interfaces for communicating with said plurality of independent CPUs, a coupling facility storage device for storing shared data which may be concurrently and commonly accessed by said plurality of independent CPUs operating externally of said coupling facility, and wherein any of said plurality of independent CPUs may store data in said coupling facility storage device and wherein said stored data may be retrieved by any of said plurality of independent CPUs including any of said plurality of independent CPUs which originally stored said stored data in said coupling facility storage device, a coupling facility memory interface between the coupling facility storage device and said plurality of intersystem channels, and a coupling facility control program for coupling said intersystem channels to said coupling facility storage device over said coupling facility memory interface,
• said coupling facility storing messages commands and data for coupling a particular intersystem channel and the coupling facility processors, each of which has data objects used to maintain state information for the shared data in the coupling facility storage device, said coupling facility memory interface having means for receiving primary message commands and data from any of said plurality of independent CPUs, for sending data and responses to the primary message commands, for sending secondary message commands originated by the coupling facility, triggered by the primary message commands, and for receiving responses to the secondary message commands from the plurality of independent CPUs,
• said coupling facility including a state information buffer control information operation memory block within said coupling facility storage device for describing a hardware communication environment associated with the computer system mechanism for storage of state information pertaining to communications buffers residing in said coupling facility memory interface, a set of address registers for said coupling facility memory interface, and wherein is employed, four instructions, PREPARE CHANNEL BUFFER, SIGNAL CHANNEL BUFFER, MOVE CHANNEL BUFFER DATA, and TEST CHANNEL BUFFER, for enabling said coupling facility control program to directly manipulate the address registers and control the flow of the data, message commands and responses directly between the coupling facility storage device and the plurality of independent CPUs.