Page of GC20-1834-0 As Updated Aug. 1, 1979 by TNL GN25-0486
Channel-set Switching
The VM/370 support of the Channel-set switching feature of the 3033
Attached Processor provides increased processor availability and
recoverability on this system.
The Channel-set Switching feature allows the main (I/O) processor to
be taken offline (via the VARY command). The system continues to run in
uniprocessor mode with the I/O capability switched to the attached
processor, thus increasing system availability during main processor
preventive maintenance.
Also, the Channel-set Switching feature allows CP to perform
Automatic Processor Recovery in the case of a Time-of-Day clock error on
the main processor (provided the main processor was in problem state at
the time of the failure). The system converts to uniprocessor mode and
continues to run with the Channel-set connected to the attached
processor. This increases system recoverability and availability over a
main processor failure and servicing.
For a more detailed discussion, refer to !M/31Q flanning sn£ There are two new instructions provided to support Channel-set Switching. They are: I. Disconnect Channel-set ,. Connect Channel-set On a 3033 Attached Processor system, all online channels comprise the
Channel-set.
At initialization time, CP determines whether or not the Channel-set Switching feature is available by executing a connect Channel-set
instruction. If the instruction executes successfully the feature is
available. CP then records this in the PSAs (a bit is set on) along
with the address of the Channel-set of the initiated device. CP tests
this bit before attempting to VARY the main processor offline and before
attempting to recover from a hardware failure on the main processor. CP uses the Channel-set address in the disconnect and connect Channel-set
ins tructions.
Note: An '016' disabled wait state will be loaded when the disconnect or
connect Channel-set instruction does not work. If this wait state
occurs, contact your IBM support personnel.
t SRL AND PROGRAM LOGIC PUBLICATIONS The following publications contain information on VM/370 support for
Channel Set Switching: GC20-1800 Introduction
GC2o-1801 Planning and System Generation Guide
GC20-1806 Operator's Guide
GC20-1808 System Messages 1-30 IBM VM/310 Release 6 Guide
Page of GC20-1834-0 Updated Aug. 1, 1979 by TNL GN25-0486 GC20-1809 OLTSEP and Error Recording Guide SY20-1884 Data Areas and Control Block Logic SY20-1886 System Logic and Problem Determination Guide -- Volume 1
Section 1. Summary of Changes to the VK/370 System 1-30.1
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