System and method for input/output flow control in a multiprocessor computer system

摘要

An input/output flow control system for a processor system having an input/output request source (e.g., a processor) and a plurality of input/output request targets (e.g., I/O busses) uses a NACKing (negatively acknowledging) scheme to prevent a common I/O path from becoming blocked due to the blockage of one or more I/O buses. The system includes a flow controller associated with each of the targets for receiving input/output requests from the source, for accepting (ACKing) a request if the intended target can accept the request, and for NACKing a request if the intended target cannot accept the request. The system also includes a processor or source interface for resending the NACKed requests to the intended target and for cooperating with the flow controller so that the NACKed requests are accepted by the flow controller in the proper order.