Multiprocessor system

Abstract

An input/output system for a processor of the kind in which a processor module has a central processing unit, a memory, an input/output channel, and a plurality of device controllers for controlling the transfer of data between the processor module and the peripheral devices includes a star poll connection in which each device controller is provided with a signalling means for signalling its identity in response to a poll operation, independently of other similarly connected device controllers such that any number of device controllers can be failed or powered off without affecting the polling of the other device controllers. The data lines in an input/output bus are used both to transmit data and to transmit signals to reduce the total number of lines needed to connect the device controllers to the channel in the star poll connection. The system is a fault tolerant system which includes an enable bit in the port of each device controller. The bit can be reset to prevent that device controller from transmitting spurious signals which could interfere with interrupt requests being transmitted to the channel by other device controllers so that a failed device controller can be effectively removed from the system. A rank line arrangement is utilized in the priority selection scheme so that an additional group of controllers can be added in a way which requires the use of only one more line in the input/output bus and still allows each device controller to respond independently to poll operations.