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Abstract

An improved communication system for the prevention of lockup in a computer system of the binary n-cube type. Input circuitry at each of the nodes is connected for receiving messages and includes an input buffer for initially receiving the messages. Output circuitry at each of the nodes is connected for transmitting holding the messages prior to and during transmission thereof. A kernel program at each of the nodes acts as an interface between the user process programs and exclusively controls the receiving and transmitting of messages into and out of the node. There is provision for the user process programs to pass control to the kernel program to request the sending and receiving of messages by the kernel program. A lock bit is associated with each message, sensible by the user process programs, and reset by the kernel program when the kernel program has transferred the associated message. Asynchronous transfer circuitry independently and asynchronously transfers the messages as packets between the buffers of the nodes. There is logic for various decisional matters regarding message sending and receipt. There is blockout prevention logic for refusing to receive a message unless a user process program in the node has reserved a buffer of sufficient size to receive the message and for listing messages waiting to be received for which space has not yet been reserved.

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