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AssigneeInternational Business Machines Corporation
InventorsPaul J. Brown, Robert J. Dugan, Richard R. Guyette
Estimating the term…
A new instruction called Test Subchannel assures that one processor will not begin an I/O operation with device status information that has been outdated by an operation of another processor. When a device has status to present, a status pending bit and an interruption pending bit are set in the channel subsystem and an interruption request is made. When a processor accepts an interruption, the channel system resets the interruption pending bit but not the status pending bit. The processor that accepts the interruption updates the unit control block (UCB) in main store and resets the status pending bit in the subchannel unless the UCB has been locked by another processor that is starting an I/O operation on the same device. This invention prevents the other processor from operating with outdated status information in the UCB. A processor that has locked the UCB uses Test Subchannel to test the Status Pending bit in the subchannel. If status is pending, the processor executes a routine to update the UCB. Optionally, when a processor that is handling an interruption finds the UCB locked, it sets a flag bit in the UCB lock word. Before a processor resets the UCB lock, it checks the lock word and executes the Test Subchannel instruction if the flag is set.
In a data processing system having a channel subsystem and having a central complex arranged to operate with said channel subsystem, said central complex including multiple central processing units and including means for storing the status of a device that is part of the channel subsystem in which a first central processing unit may be locking and accessing said status storing means to start an operation at a device at the same time that a second central processing unit is operating to process information stored in said channel subsystem pertaining to the status of said device, and to update device status in said status storing means while said status storing means is locked by said first central processing unit means for preventing said first unit from starting said operation with reference to outdated status information comprising:
In a data processing system including a device, central processing apparatus including plural central processing units for initiating data exchange operations with said device, and I/O processing apparatus connecting said central apparatus and said device for controlling said data exchanges concurrent with other operations of said central apparatus, a method of ensuring currency of any status information which is used by said central apparatus to initiate a said data exchange, comprising the steps of:
Dependencies are inferred from the claim text.