Data processing system having event word handling facility which can send event word of higher significance without failure

摘要

A channel subsystem provided for connection of a large number of peripheral devices has an event word handing facility whereby an event word for reporting a failure, etc., occurring in a peripheral device, to a main CPU, is generated and queued in a buffer that is accessible from the main CPU. The event word handling facility provided in the channel subsystem of the present invention includes: an inhibit word count register for storing a plurality of inhibit word counts whose values are set closer to the capacity of the buffer as the significance of their associated event words increases; a selector for selecting an inhibit word count appropriate to the event word to be generated; and a comparator for comparing the selected inhibit word count with the number of event words currently held in the buffer. Only when the number of event words held in the buffer is smaller than the selected inhibit word count, is an event word generated. Thus, an event word of higher significance can be notified without fail.