System for controlling connection requests by each io controllers

Abstract

A data processing system includes a central processing complex consisting of one or more processor units, each of the processor units having one or more input/output channels, a transmission medium connected to each of the input/output channels, and one or more peripheral device controllers such as for controlling one or more direct access storage devices (DASD). In systems having more than one input/output channels, it is common to include a switching mechanism connected between the input/output channels and the control devices for enabling connection between one of a number of controllers and one of a number of channels. Each control device will include an automatic frame transmission function which includes apparatus and method for controlling transmission of frames of information between the control device and the channel. A queue of reconnection requests is constructed and a state machine controls the queue. For example, the state machine reads the queue, loads and sends frames from the controller to the channel, manages a redrive timer and automatically redrives or terminates automatic frame transmission processing depending on system parameters and responses received from the channel or from another controller in controller to controller transmissions.