High performance shared main storage interface

Abstract

A high performance interface joins multiple processing devices configured as masters, with multiple memory cards or other devices configured as slaves. The interface includes a working data bus for transmitting working information between the processors and memory cards. Auxiliary busses, including a command/address bus for commands and address information and a communication bus for status information, are connected to all of the processing devices and slave devices and operate in parallel with the working data bus. A system for distributing control of the working information bus, among all of the master devices and slave devices, includes a grant token and plural select tokens. The grant token, a line connected in common to all devices, permits a device currently controlling the interface to retain control until it completes its transmission. The select tokens, each connected to a uniquely associated slave device and to all of the master devices, consists of a command active line activated by a master device when providing a store or fetch command, a return data line activated by a selected master device to retrieve earlier requested data from a selected slave device, and a buffer full line whereby a slave device with its buffer occupied communicates this fact to all of the master devices. Store and fetch operations are conducted according to command transfer and return data transfer protocols, which optionally include an acknowledgement via the communication bus that a command was received during the next preceding clock cycle.