CHAPTER INTERRUPTIONS Interruption Action ••.••••.•••••••••••••.•••.••••••••.•••• 6-2
Interruption Code •.•••••..••••••.•••••.•.••••••••••••••• 6-5
Enabling and Disabling •.••...••.••.•...••.•.•••••••••••• 6-6
Handling of Floating Interruption Conditions •.•••..•..•. 6-7
Instruction-Length Code ••.••.•••••..••.•••••.••••••.•.•• 6-7
Zero ILC .......••.••••••..••...••..•.••.•••.•••••••••• 6-7 ILC on Instruction-Fetching Exceptions ••.••.•••••••.•• 6-8
Exceptions Associated with the PSW .•...•...••.•..••...•• 6-9
Early Exception Recognition ....••....•..••.••••••.•••. 6-9
Late Exception Recognition ...••..•.•.••..••••••.•.•..• 6-9
External Interruption .••..•••....•.••••..••.•••.••••...••• 6-10 Clock Comparator ....••....••.•.••.••.•.••.••..•••.•.••.. 6-11 CPU Timer .......•...•.•..•...•...........•.••..••.•.••.• 6-11
Emergency Signal .••.••••..••.•.•••••.•.••.••••••.••••••. 6-11
External Call ••..•.....•..•...•••.••...•••••.•.••••..••. 6-11
External Signal ••••.••••.•.....••.•..•.•...••.•..••..•.. 6-12
Interrupt Key •..•..•..•..•.•.•.•••...•.••..•.........•.. 6-12
Interval Timer ..•....•.••.•..•.•••••••.•..••••.•••••.... 6-12
Malfunction Alert ..•..•.••••...••••..•.••..•••.•.•...••• 6-12 Service Signal ...••..•.•..•.•..•••...•..•..•.•...••.•••• 6-13 TOD-Clock Sync Check ...•..••..•....•.•.•..••..•.•.•..••. 6-13 I/O Interruption .••..•............•..•...........•.......• 6-13 Machine-Check Interruption ...•...••.......••.••..•.•••..•. 6-14 Program Interruption .••.••...•...•.•••...•••.•••••.•...••. 6-14
Exception-Extension Code ..••............................ 6-15
Program-Interruption Conditions ....•...•..••..•..•...•.. 6-15
Addressing Exception .•..•.•..•••.....••..•••••.••••... 6-15
AFX-Translation Exception •...••.......••.••..•..••.••. 6-18 ASH-Translation-Specification Exception .•••..•..•••••. 6-18
ASX-Translation Exception .•.•..•.....•••••..•...•..... 6-18 Dilta Excepti on ......••..........•..........•....•..... 6-18 Decimal-Divide Exception ..•.......••.•.•..••.•..•..•.. 6-19 Decimal-Overflow Exception ...•.......•...•...•...•.•.. 6-19 Execute Exception ............•.......•..•............. 6-19 Exponent-Overflow Exception ..•.......•....•.•.••••.•.. 6-19
Exponent-Underflow Exception ............•••.....••..•. 6-19
EX-Translation Exception .........•....•.•...••.••..••. 6-20 Fixed-Point-Divide Exception ...•........••..•....••.•. 6-20 Fixed-Point-Overflow Exception •....•....••..•.•.••.... 6-20 Floating-Point-Divide Exception ......••....••••.•..•.. 6-20 LX-Translation Exception .•...••..........••.....••.... 6-20 Monitor Event ..........•.....•.....•..•......••.••..•. 6-21 Operation Exception ... ..•...••.•.•...••..•..•..•..... 6-21 Page-Translation Exception ......•...•.•.•.•...•.•.•... 6-22 PC-Translation-Specification Exception .••..•..••.••.•. 6-22 PER Event ....•...•..••...••.•..•.•..••..•••.•••••••... 6-22
Primary-Authority Exception ........•...•••....•.•...•. 6-23 Privileged-Operation Exception .•••.••...••.•...••.•.•. 6-23 Protection Exception ..•.•....•..••.••••.••..•.••...•.. 6-23
Secondary-Authority Exception ......................... 6-24
Segment-Translation Exception ..••••.•.••••.•.•.•...... 6-24 Significance Exception ...•.••......••...•.•.•.••....•. 6-25 Space-Switch Event ...........••.•...•...•..••.•...•••• 6-25 Special-Operation Exception ••.•.•..••••.•.•••••••..••. 6-25 Specification Exception ....••..••.•.•.•••••••.•••.•..• 6-26
Translation-Specification Exception ..••.••••...••.•.•. 6-27
Unnormalized-Operand Exception •••.•••.••.••.•.••••.••. 6-27
Vector-Operation Exception •....••.••.•.•..••••••.••.•• 6-28 Collective Program-Interruption Hames .•......•..•..••.•• 6-28
Recognition of Access Exceptions ....•.•...••...•.••.•••. 6-28
Multiple Program-Interruption Conditions ..•..••.....•.•. 6-30 Access Exceptions ...•....•..••..•...••.•.•.•••••...••. 6-33 ASH-Translation Exceptions •....••...••.••...•.••.••••. 6-35 Trace Exceptions ........•.....•..•.••••.•••••••••••••• 6-35
Restart Interruption .•......••....•.••.••.•••••.••.•..•... 6-35 Supervisor-Call Interruption ...••••..•.••••.••.•.•.••.•.•. 6-36 Priority of Interruptions ..••.••...••••••••.•••....••.•••• 6-36 Chapter 6. Interruptions 6-1
The interruption mechanism permits the CPU to change its state as a result of
conditions external to the
configuration, within the configuration,
or within the CPU itself. To permit
fast response to conditions of high
priority and immediate recognition of
the type of condition, interruption
conditions are grouped into six classes:
external, input/output, machine check,
program, restart, and supervisor call. INTERRUPTION ACTION An interruption consists in storing the
current PSW as an old PSW, storing
information identifying the cause of the interruption, and fetching a new PSW. Processing resumes as specified by the new PSW. The old PSW stored
normally contains
instruction that
on an interruption
the address of the
would have been
6-2 System/370 Principles of Operation executed next had the interruption not
occurred, thus permitting resumption of
the interrupted program. For program
and supervisor-call interruptions, the
information stored also contains a code
that identifies the length of the last­
executed instruction, thus permitting
the program to respond to the cause of
the interruption. In the case of some
program conditions for which the normal
response is reexecution of the instruc­
tion causing the interruption, the
instruction address directly identifies
the instruction last executed.
Except for restart, an interruption can
occur only when the CPU is in the oper­
ating state. The restart interruption
can occur with the CPU in either the
stopped or operating state.
The details of source identification,
location determination, and instruction
execution are explained in later sections and are summarized in the
figure "Interruption Action."
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