The interruption code of a new psw is not loaded
since a new interruption code is always storcd. The
instruction-length code in a new psw is similarly ig
nored since it is unpredictable for all interruptions
other than program or supcrvisor call. The protcction
key of a new psw is stored unchanged when the pro
tection feature is installed. When the feature is not
installed, the protection key is made zero upon storing.
Programming Note
When interruption sources are not masked off, thc
order of priority in handling the intcrruption sub
routines is machine check,I/O, external, and program
or supervisor call. This order can be changed to some
extent by masking. The priority rule applies to inter
ruption requests made simultaneously. An interruption
request made after some interruptions have already
been taken is honored according to the priority pre
vailing at the moment of request.
Interruption Exceptions
The only exception that can cause a program inter
ruption during an interruption is a specification ex
ception.
Specification: The protection feature is not installed,
and a new psw with nonzero protection kcy is loaded.
A program interruption is taken immediately upon
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loading thc newPSW, regardless of the type of inter
ruption introducing thc erroneous protection key and
prior to any other pending interruptions. The protec
tion key is made zero when the psw is stored.
If the new psw for the program interruption has a
nonzero protection key, another program interruption
occurs.Since this second program interruption intro
duces the same unacceptable protection key in the
newPSW, the process is repeated with the CPU caught
in a string of program interruptions. This string can be
broken only by initial program loading or system reset.
The instruction address in a new psw is not tested
for availability or resolution as the psw is fetched
during an interruption. However, an unavailable or
odd instruction address is detected as soon as the
instruction address is used to fetch an instruction.
These exceptions are described in the section on
normal sequential operation.
If the new psw for the program interruption has an
unacceptable instruction address, another program
interruption occurs.Since this second program inter
ruption introduces the same unaccept'able instruction
address, a string of program interruptions is estab
lished. This string may be broken by an external orI/O interruption. If these interruptions also have an
unacceptable new psw, new supervisor information
must be introduced by initial program loading or by
manual intervention.
since a new interruption code is always storcd. The
instruction-length code in a new psw is similarly ig
nored since it is unpredictable for all interruptions
other than program or supcrvisor call. The protcction
key of a new psw is stored unchanged when the pro
tection feature is installed. When the feature is not
installed, the protection key is made zero upon storing.
Programming Note
When interruption sources are not masked off, thc
order of priority in handling the intcrruption sub
routines is machine check,
or supervisor call. This order can be changed to some
extent by masking. The priority rule applies to inter
ruption requests made simultaneously. An interruption
request made after some interruptions have already
been taken is honored according to the priority pre
vailing at the moment of request.
Interruption Exceptions
The only exception that can cause a program inter
ruption during an interruption is a specification ex
ception.
Specification: The protection feature is not installed,
and a new psw with nonzero protection kcy is loaded.
A program interruption is taken immediately upon
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loading thc new
ruption introducing thc erroneous protection key and
prior to any other pending interruptions. The protec
tion key is made zero when the psw is stored.
If the new psw for the program interruption has a
nonzero protection key, another program interruption
occurs.
duces the same unacceptable protection key in the
new
in a string of program interruptions. This string can be
broken only by initial program loading or system reset.
The instruction address in a new psw is not tested
for availability or resolution as the psw is fetched
during an interruption. However, an unavailable or
odd instruction address is detected as soon as the
instruction address is used to fetch an instruction.
These exceptions are described in the section on
normal sequential operation.
If the new psw for the program interruption has an
unacceptable instruction address, another program
interruption occurs.
ruption introduces the same unaccept'able instruction
address, a string of program interruptions is estab
lished. This string may be broken by an external or
unacceptable new psw, new supervisor information
must be introduced by initial program loading or by
manual intervention.