2. When the operation is completed or
partially completed, the event is indicated, regardless of whether
any program exception, space-switch
event, or monitor event is also
recognized.
3. Successful branching, storage
alteration, and general-register
alteration are not indicated for an
operation or, in case the instruc­
tion is interruptible, for a unit
of operation that is suppressed or
nullified.
4. When the execution of the instruc­
tion is terminated, general­ register or storage alteration is
indicated whenever the event has
occurred, and a model may indicate
the event if the event would have
occurred had the execution of the
instruction been completed, even if
altering the contents of the result
field is contingent on operand
values. For purposes of this defi­
nition, the occurrence of those
exceptions which permit termination
(addressing, protection, and data)
are considered to be termination,
even if no result area is changed.
5. When LOAD PSW, SET SYSTEM MASK, STORE THEN OR SYSTEM MASK, or SUPERVISOR CALL causes a PER condi­
tion and at the same time intro­
duces a new PSW with the type of PSW-format error that is recognized
immediately after the PSW becomes
active, the interruption code iden­ tifies both the PER condition and
the specification exception. When LOAD PSW or SUPERVISOR CALL intro­
duces a PSW-format error of the type that is recognized as part of
the execution of the following
instruction, the PSW is stored as
the old PSW without the specifica­
tion exception being recognized.
The indication of PER events concurrent­
ly with other program-interruption
conditions is summarized in the figure
"Indication of PER Events with Other Concurrent Conditions." Chapter 4. Control 4-21

PER Event
Type
of Instr Storage GR Concurrent Condition Ending Branch Fetch Alter. Alter. Specification Odd instruction address S No No No No in the PSW Instruction access First hal N or S No No No No Second, third halfwords N or S No U No No Specification EXECUTE target address odd S No U No No EXECUTE target access N or S No U No No Other nullifying N No Yes Nol Nol Other suppressing S Yes Nol Nol All terminating T No Yes Yes
2 Yes
2 All completing C Yes Yes Yes Yes
Explanation:
Although PER events of this type are not indicated for
the current unit of operation of an interruptible in­
struction, PER events of this type that were recognized
on completed units of operation of the interruptible
instruction are indicated.
2
This event may be indicated, depending on the model, if
the event has not occurred but would have been indicated if execution had been completed. C The operation or, in the case of the interruptible in­
structions, the unit of operation is completed. N The operation or,
structions, the in the case of the interruptible in­ unit of operation is nullified. S The operation or, in the case of the interruptible in­
structions, the unit of operation is suppressed.
T The execution of the instruction is terminated. Yes The PER event is indicated with the other program­
interruption condition if the event has occurred; that
is, the contents of the designated storage location or
general register were altered, or an attempt was made
to execute an instruction whose first byte is located
in the designated storage area. No The PER event is not indicated.
U It is unpredictable whether the PER event is indicated.
Indication of PER Events with Other Concurrent Conditions Programming Notes 1. The execution of the interruptible
instructions MOVE LONG, TEST BLOCK,
and COMPARE LOGICAL LONG can cause
events for general-register alter­
ation and instruction fetching.
Additionally, MOVE LONG can cause
the storage-alteration event.
Interruption of such an instruction
may cause a PER event to be indi­
cated more than once. It may be
4-22 System/370 Principles of Operation
necessary, therefore, for a program
to remove the redundant event indi­ cations from the PER data. The
following rules govern the indi­
cation of the applicable events
during execution of these
instructions: a. The instruction-fetching event is indicated whenever the
instruction is fetched for
execution, regardless of wheth- 4 er it is the initial execution j or a resumption.