| 摘要 |
In a tightly coupled multiprocessing system wherein plural central processing elements (210, 212) share an operating system (supervisory program), a main store (40), and a multipath I/O channel processing facility (220) for linking to peripheral devices (42), and in which the channel processing facility contains a single unique subchannel for each device regardless of the number of paths available for connecting to the device (42), apparatus disclosed herein ensures that a central processing element (210, 212) which attempts to start an operation of the device will have reference to the latest pertinent status even if another central processing element is simultaneously attending to an interruption associated with such status. This apparatus retains status information in the subchannel, along with an indication of its retention, while the interruption is being handled in the central complex. The cental complex is required to examine and reset the retention indication, and recover any associated status, before it can stimulate the channel facility to start the device (42). The apparatus for performing these operations includes means in the central complex for executing the examining, resetting and recovery operations in response to a special program instruction Test Subchannel (TSCH). |
