Abstract: A common data link interface providing a framework for device drivers and data link providers. This interface allows multiple frameworks to coexist and share a single device driver. The common data link interface is framework independant and provides functions that are common to a plurality of frameworks. The common data link interface comprises three components, a network device driver, network demultiplexers, and network services. The network device driver provides a simple interface to network based devices that can be used by both the sockets IFNET and the streams DLPI data link layers. The network demultiplexor provides common data link receive functionality. Network services provides the remaining additional functionality required to bind the common data link interface together.

Abstract: A first data processor (10) and at least a second data processor (11) are connected by a data link (12). The processors each have a communication adapter (14) which is connected to the data link and system clock (21) which times functions within the processor. Under a synchronous data link control (SDLC) protocol which has information frames and supervisory frames, one of the processors is designated as the primary station and the other, the secondary station. Whenever supervisory frames are transmitted between the primary and secondary stations, means are operative for inserting a mandatory non-polling quiet period of a predetermined length prior to each poll so that the processor at the secondary station is freed for non-polling functions.