Flow control of messages in a local area network

• US 5,084,871 A
• Filed: 10/03/1989
• Issued: 01/28/1992
• Est. Priority Date: 10/16/1987
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Kirk, Robert C., Read, Harold A., Zagame, Steven P., Mills, Milton V., Metz, Donald R., Carn, Ronald C., Kaczor, Charles E., Kent, Allan R., Henry, Barry A.
• Primary Examiner(s): Chan, Eddie P.
• Assistant Examiner(s): FAGAN, MATTHEW
• Application Number:
  US07/416,504
• Time in Patent Office: 847 Days
• Field of Search: 364/200, 364/900, 371/33, 371/32, 340/825.16, 370/60, 370/94.1, 370/94.3
• US Class Current: 370/462
• CPC Class Codes: G06F 11/2007 using redundant communication media
• CPC Class Codes: G06F 11/22 Detection or location of defective computer hardware by testing during standby operation or during idle time, e.g. start-up testing
• CPC Class Codes: G06F 13/4022 using switching circuits, e.g. switching matrix, connection or expansion network G06F13/4009 takes precedence

Abstract

A computer interconnect coupler has channel transmitters and logic and channel receivers and logic circuitry for the routing of messages from the channel receivers which are addressed to the channel transmitters. When a message is received by a channel receiver, the channel receiver stores the beginning portion of the message in a first-in-first-out buffer, and sends a route message request to central switch logic. If the destination transmitter or receiver is busy, the central logic places the message request on a destination queue and returns a signal to the requesting source transmitter to turn on a flow control signal which is transmitted back to the data processing device having originated the message. Any message addressed to this data processing device, however, is inserted into the flow control carrier with pauses both before and after the message, and provisions are also made to allow the data processing device to return an ackowledgement responsive to the incoming message. To permit incremental expansion of the coupler to accommodate an increased number of channels, additional channel interface boards may be added. The coupler also includes a plurality of timers which determine fault conditions, and a diagnostic processor monitors the timers and associated error flags to diagnose faults to the board level. The conditions existing at the time of fault diagnosis are written into a non-volatile memory located on the circuit board. Therefore, the information is physically carried along with the board to the repair facility.

Claims

1. A method of operating a data processing device for data communication, said method comprising the steps of:

transmitting an outgoing message,

sensing whether a flow control signal is received after transmitting said outgoing message, and

when said flow control signal is received, inhibiting outgoing message transmission from said data processing device, and sensing whether an incoming message is inserted into said flow control signal, and when said incoming message is inserted into said flow control signal, receiving said incoming message, and after receiving said incoming message, sensing whether said flow control signal is again received, and when said flow control signal is again received, inhibiting outgoing message transmission from said data processing device, and when said flow control signal is not again received, transmitting an outgoing message from said data processing device, whereby said data processing device receives said incoming message when outgoing message transmission from said data processing device is inhibited by said flow control signal.

2. A method of operating a data processing device for data communication, said method comprising the steps of:

transmitting an outgoing message, sensing whether an acknowledgement is received after transmitting said outgoing message, and when said acknowledgement is not received, sensing whether a flow control signal is received, and when said flow control signal is received, inhibiting retransmission of said outgoing message, and when said flow control signal is not received, retransmitting said outgoing message, and

when retransmission of said outgoing message is inhibited by said flow control signal, sensing whether an incoming message is inserted into said flow control signal, and when said incoming message is inserted into said flow control signal, receiving said incoming message, and after receiving said incoming message, sensing whether said flow control signal is again received, and when said flow control signal is again received, inhibiting retransmission of said outgoing message, and when said flow control signal is not again received, retransmitting said outgoing message, whereby said data processing device receives said incoming message when said data processing device is inhibited by said flow control signal from retransmitting said outgoing message.

3. The method of operating said data processing device as claimed in claim 2, wherein said method comprises transmitting an acknowledgment after receiving said incoming message and before said sensing whether said flow control signal is again received.

4. The method of operating said data processing device as claimed in claim 2, wherein said flow control signal comprises a carrier which is used for transmission of said incoming message to said data processing device.

5. The method of operating said data processing device as claimed in claim 4, further comprising the steps of sensing whether said carrier is present just before and just after receiving said incoming message.

6. A method of transmitting messages among multiple data processing devices each of which has an external communication port, said method comprising the steps of:

receiving messages originating from said data processing devices, each of said messages having a desired destination and address data identifying a data processing device which is the desired destination, said messages including more than one message which cannot be immediately transmitted to its desired destination,

queuing message information for each of said messages which cannot be immediately transmitted to its desired destination, wherein said message information is queued in a queue having a head storing the message information for an oldest one of said messages having message information queued in said queue, said oldest one of said messages having originated from one of said data processing devices,

transmitting a flow control signal to each of said data processing devices originating each of said messages for which message information is queued in said queue to inhibit retransmission of each of said messages for which message information is queued in aid queue, and

terminating transmission of said flow control signal to said one of said data processing devices which originated said oldest one of said messages, said transmission of said flow control signal being terminated when said oldest one of said messages can be transmitted to its desired destination, and retransmitting said oldest one of said messages from said one of said data processing devices in response to the termination of transmission of said flow control signal; and

inserting some of said messages into said flow control signal so that the data processing devices receiving said flow control signal receive the messages inserted into said flow control signal while retransmission of messages from the data processing devices receiving the flow control signal is inhibited.

7. The method of claim 6 wherein said flow control signal is a carrier and the step of inserting messages into said flow control signal includes modulating said carrier to transmit the messages inserted into said flow control signal.

8. The method of claim 6, further comprising the step of terminating the transmission of said flow control signal when said flow control signal has been transmitted for a duration of time longer than a predetermined time interval.

9. A computer interconnect coupler for transmitting messages among multiple data processing devices each of which has a communication port, said coupler comprising:

receiving means for receiving messages originating from the communication port of each of said data processing devices, each of said messages having a desired destination and including address data identifying a data processing device which is the desired destination, said messages including more than one message which cannot be immediately transmitted to its desired destination,

routing means coupled to said receiving means for determining when each of said messages which is received by said receiving means can be transmitted to its desired destination,

a queue coupled to said receiving means and said routing means for storing message information for each of said messages which is received by said receiving means but which cannot be immediately transmitted to its desired destination, said queue having a head for storing the message information for an oldest one of the messages for which message information is stored in said queue, said oldest one of the messages originating from a communication port of one of said data processing devices,

transmitting means coupled to said routing means for transmitting a flow control signal to the communication port of each of the data processing devices which originated each of said messages which is received by said receiving means but which cannot be immediately transmitted to its desired destination, said flow control signal inhibiting retransmission of each of said messages which is received by said receiving means but which can be immediately transmitted to its desired destination,

means coupled to said queue, said routing means and said transmitting means for terminating transmission of said flow control signal to the communication port of said one of said data processing devices which originated said oldest one of said messages, said transmission of said flow control signal being terminated when said routing means determines that said oldest one of said messages can be transmitted to its desired destination, whereby retransmission of said oldest one of said messages from said one of said data processing devices occurs in response to the termination of transmission of said flow control signal, and

means coupled to said transmitting means and said routing means for inserting some of said messages into said flow control signal so that the data processing devices receiving said flow control signal receive the messages inserted into said flow control signal while retransmission of messages from the data processing devices receiving the flow control signal is inhibited.

10. The computer interconnect coupler of claim 9 wherein said flow control signal is a carrier and said means for inserting messages into said flow control signal includes means for modulating said carrier to transmit the messages inserted into said flow control signal.