status stored is referred to as the "point of interrup tion." Only certain points in the processing may be used
as a point of interruption. For repressible machine
checks the point of interruption must be after one
unit of operation is completed, including the associ
ated program or supervisor-call interruption, if appli
cable, and before the next unit of operation is begun.
Exigent machine-check conditions which are de
layed (disallowed and presented later when allowed)
can occur only at the same points of interruption as
repressible machine-check conditions. When an exi
gent machine-check condition is not delayed, the
point of interruption may also be after the unit of
operation is completed but before the associated
program or supervisor-call interruption occurs. In
this case, a validPSW is defined as that which would
have been stored in the oldPSW for the program or
supervisor-call interruption. Even though all status
may be indicated as valid, damage has occurred be
cause the associated interruption is lost.
Programming Note
When an exigent machine-check condition occurs,
the pointof interruption which is chosen affects the
amount of damage which must be indicated. An at
tempt is made, when possible, to choose a point of
interruption which permits the minimum indication
of damage. In general, the preference is the interrup
tion point immediately preceding the error. When a
point of interruption is chosen which is after an as
sociated program or supervisor-call interruption, the
damage has not been isolated to a particular pro
gram, and system damage is indicated.
When all the status information stored as a result
of an exigent machine-check condition does not
reflect the same point, an attempt is made when
possible to choose the point of interruption so that
the instruction address which is stored in the
machine-check oldPSW is valid. Alachine-Check Logout
The storing of model-dependent information in main
storage as a result of a machine check is referred to
as a machine-check logout. Machine-check logouts
are of four different types: synchronous fixed logout,
asynchronous fixed logout, synchronous machine
check extended logout, and asynchronous machine
check extended logout.
When a machine-check logout occurs during the
machine-check interruption it is called"h "If h' sync ronous. a mac me-check logout occurs
without a machine-check interruption, or if the log
out and the interruption are separated by instruction
processing or by instruction retry, then the logout is
called"asynchronous." Machine-cheek-logout information can be placed
in either or both of two areas.One area, the 96-byte
area starting at location 256, is called the"fixed logout area." Additionally, a machine-check
extended-logout area (MCEL) is defined. The start
ing location of the MCEL area is specified by the
contents of control register 15. The existence and
length of the machine-check extended logout are
model-dependent.
To preserve the initial machine-check conditions,
some models perform an asynchronous logout before
invoking automaticCPU recovery action. Depending
on the model, logout may occur before recovery,
after recovery, or at both times. If logout occurs at
both times it may be into the same portion or two
different portions of the logout area.Alachine-Check Extended Interruption
Information
The machine-check extended interruption informa
tion consists of seven fields, which are stored at
machine-check interruption time. Each of these
fields has a validity bit associated with it in the
machine-check interruption code. If for any reason
the machine cannot store one of these fields or can
not store the field validly, the associated validity bit
is set to zero.
Timing Facilities: When the system-timing facilities
are present, any machine-check interruption causes
the contents of the clock comparator andCPU timer
to be placed in storage as part of the machine-check
extended interruption information. The contents of
the clock comparator are stored in the doubleword
starting at location 224. The contents of theCPU timer are placed in the double word starting at loca
tion 216.
Fai/ing-Storage Address: When a storage error un
corrected, storage error corrected, or key in storage
error uncorrected has been indicated, the failing
storage address is stored in bits 8-31 of the word at
location 248. Bits0-7 of the word are set to zeros.
In the case of storage errors, the failing-storage ad
dress may point to any byte within the checking
block. For key in storage error uncorrected, the
failing-storage address may point to any address
within the 2,048-byte block of storage associated
with the key in storage that is in error. When an
error is detected in more than one location before
the interruption, the failing-storage address may
point to any of the failing locations. The address
stored is an absoluteaddress; that is, the value
Machine-Check Handling 177
as a point of interruption. For repressible machine
checks the point of interruption must be after one
unit of operation is completed, including the associ
ated program or supervisor-call interruption, if appli
cable, and before the next unit of operation is begun.
Exigent machine-check conditions which are de
layed (disallowed and presented later when allowed)
can occur only at the same points of interruption as
repressible machine-check conditions. When an exi
gent machine-check condition is not delayed, the
point of interruption may also be after the unit of
operation is completed but before the associated
program or supervisor-call interruption occurs. In
this case, a valid
have been stored in the old
supervisor-call interruption. Even though all status
may be indicated as valid, damage has occurred be
cause the associated interruption is lost.
Programming Note
When an exigent machine-check condition occurs,
the point
amount of damage which must be indicated. An at
tempt is made, when possible, to choose a point of
interruption which permits the minimum indication
of damage. In general, the preference is the interrup
tion point immediately preceding the error. When a
point of interruption is chosen which is after an as
sociated program or supervisor-call interruption, the
damage has not been isolated to a particular pro
gram, and system damage is indicated.
When all the status information stored as a result
of an exigent machine-check condition does not
reflect the same point, an attempt is made when
possible to choose the point of interruption so that
the instruction address which is stored in the
machine-check old
The storing of model-dependent information in main
storage as a result of a machine check is referred to
as a machine-check logout. Machine-check logouts
are of four different types: synchronous fixed logout,
asynchronous fixed logout, synchronous machine
check extended logout, and asynchronous machine
check extended logout.
When a machine-check logout occurs during the
machine-check interruption it is called
without a machine-check interruption, or if the log
out and the interruption are separated by instruction
processing or by instruction retry, then the logout is
called
in either or both of two areas.
area starting at location 256, is called the
extended-logout area (MCEL) is defined. The start
ing location of the MCEL area is specified by the
contents of control register 15. The existence and
length of the machine-check extended logout are
model-dependent.
To preserve the initial machine-check conditions,
some models perform an asynchronous logout before
invoking automatic
on the model, logout may occur before recovery,
after recovery, or at both times. If logout occurs at
both times it may be into the same portion or two
different portions of the logout area.
Information
The machine-check extended interruption informa
tion consists of seven fields, which are stored at
machine-check interruption time. Each of these
fields has a validity bit associated with it in the
machine-check interruption code. If for any reason
the machine cannot store one of these fields or can
not store the field validly, the associated validity bit
is set to zero.
Timing Facilities: When the system-timing facilities
are present, any machine-check interruption causes
the contents of the clock comparator and
to be placed in storage as part of the machine-check
extended interruption information. The contents of
the clock comparator are stored in the doubleword
starting at location 224. The contents of the
tion 216.
Fai/ing-Storage Address: When a storage error un
corrected, storage error corrected, or key in storage
error uncorrected has been indicated, the failing
storage address is stored in bits 8-31 of the word at
location 248. Bits
In the case of storage errors, the failing-storage ad
dress may point to any byte within the checking
block. For key in storage error uncorrected, the
failing-storage address may point to any address
within the 2,048-byte block of storage associated
with the key in storage that is in error. When an
error is detected in more than one location before
the interruption, the failing-storage address may
point to any of the failing locations. The address
stored is an absolute
Machine-Check Handling 177