Recovery from a possible switching error in a computer I/O system

In a data processing I/O system having a switch with a plurality of ports and a plurality of communication stations, each communication station attached to one of said ports, each communication station further having command means for commanding said switch either to make a connection between the communication station's attached one port and a selected other port, or to disconnect the communication station's attached one port with the other port of said switch;

• a connection recovery apparatus in each communication station, said connection recovery apparatus comprising:
• transmitting means having a first message link connected to said one port of said switch, said transmitting means for transmitting data including repetitive commands to said one port of said switch;
• receiving means having a second message link connected to said one port of said switch, said receiving means for receiving data including commands from said one port of said switch;
• error recognition means connected to said receiving means for recognizing possible connection errors;
• unconditional disconnect response recognition means connected to said receiving means for recognizing an unconditional disconnect response command from said attached one port;
• and
• command generating means connected to said transmitting means and said error recognition means, said command generating means for causing said transmitting means to transmit a repetitive unconditional disconnect command to said one port to disconnect any connection between said one port and any other port connected by said switch responsive to the detection of a possible error by said error recognition means;
• and
• idle character generating means connected to said unconditional disconnect response recognition means and said transmitting means for causing said transmitting means to transmit an idle sequence to said one port responsive to the detection of an unconditional disconnect response command by said unconditional disconnect response recognition means.

In a data processing I/O system having a switch with a plurality of ports and a plurality of communication stations, each communication station attached to an individual one of said ports by a link, a switch connection recovery mechanism comprising:

• a command detector in each of said communication stations and each of said ports, the command detector in each communication station being connected to the link to an individual one of said ports, each command detector for detecting an unconditional disconnect (UD) command and an unconditional disconnect response (UDR) command on said link;
• a command generator connected to said command detector in each of said communication stations and each of said ports for generating repetitive UDR commands on said link as long as its connected command detector detects UD commands, and for generating an idle sequence on said link responsive to the detection of a UDR command by said connected command detector;
• and
• a switch disconnector connected to each of said command detector means in each of said ports for breaking a switch connection from said one port to a second port through said switch upon detection of a UD command by said one port's connected command detector.