Browse Prior Art Database

Data Processing System With Communication Between Central Processor And Control Unit for Path Reserve Reset

IP.com Disclosure Number: IPCOM000099941D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Lynch, KR: AUTHOR [+2]

Abstract

When two independent central processors share an I/O (input/output) device such as a disk storage device, either processor can reserve the device in order to perform a sequence of operations without interference by the other processor. Reserve is implemented in part by control blocks in the processors and in each control unit for the device. In the control unit, the control blocks identify the devices handled by the control unit and the paths connecting these devices to main memory. A processor can also reserve a control unit.

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Data Processing System With Communication Between Central Processor And Control Unit for Path Reserve Reset

       When two independent central processors share an I/O
(input/output) device such as a disk storage device, either processor
can reserve the device in order to perform a sequence of operations
without interference by the other processor.  Reserve is implemented
in part by control blocks in the processors and in each control unit
for the device. In the control unit, the control blocks identify the
devices handled by the control unit and the paths connecting these
devices to main memory.  A processor can also reserve a control unit.

      To reserve a device, a processor issues a command Set Path ID
(SPID) to the control unit, and the control unit marks its control
blocks to show that the reserved device can operate only on a group
of paths associated with this processor.  If a control unit gets a
request for access to the device on a different path, it returns a
device busy signal.  When a processor gets this busy signal, it puts
its request on a queue and later repeats the attempt to access the
device.

      In some circumstances, information in the control blocks of the
control unit can be changed while the corresponding information for
the central processors remains the same.  For example, the
information is different while a control unit sets up or modifies its
control blocks.  As another example, certain events, for example,
device power-on reset, cause reserve to be reset in the control unit
but...