Boots – shoes – and leggings
Patent
1980-12-31
1983-08-23
Nusbaum, Mark E.
Boots, shoes, and leggings
G06F 304
Patent
active
044007736
ABSTRACT:
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Test Subchannel assures that one processor will not begin an I/O operation with device status information that has been outdated by an operation of another processor.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 This invention prevents the other processor from operating with outdated status information in the UCB.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.
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"Attached Processor", IBM TDB, vol. 23, No. 10, Mar. 1981, pp. 4481-4483 by E. G. Drimak et al.
Brown Paul J.
Dugan Robert J.
Guyette Richard R.
International Business Machines Corp.
Lieber R.
Nusbaum Mark E.
Watson Mark P.
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