Architecture Implementation Alterations; Interval Timer - IBM System/370 145 Manual

The MONITOR CALL instruction is provided with the monitoring feature.
Execution of this instruction indicates the occurrence of one of the
events being monitored. The operands of the MONITOR CALL instruction
permit specification of up to 16 classes of events, each class with up
to 16 million unique types of events. The 16 monitor classes are
individually maskable via mask bits in control register 8. When a
MONITOR CALL instruction is executed, a program interruption occurs, if
the monitor class indicated is specified, and the event identification
(class and type) is stored in the lower fixed storage area.
Both the PER facility and the monitoring feature are provided for
debugging purposes. The two features differ from one ano:ther in (1) the
number of events that can be defined, (2) whether the events are defined
by the hardware or the programmer, and (3) whether the hardware or the
programmer checks for the events and causes the interruptions. When PER
is used, once the events to be monitored have been designated by the
user, CPU hardware checks for the occurrence of the events and causes
the interruption. When the monitoring feature is used, the user defines
the events to
be
monitored (up to 16 classes with up to 16 million codes
each instead of four events), determines when the events occur, and
causes the program interruption by issuing MONITQR CALL instructions.
ARCHITECTURE IMPLEMENTATION ALTERATIONS
Two a1terations have been made to the system action taken on a
Model 145 during the.execution of certain instructions common to both
system/370 and System/360 models. The first involves all instructions
that check the validity of operands involved in packed decimal
operations. On the Model 145, an invalid sign in an operand causes the
instruction to be suppressed (never executed) rather than terminated
during execution as is done on System/360 models. Suppression, rather
than termination, of an instruction when an invalid sign occurs ensures
that the data fields involved remain unchanged. Therefore, a routine
that inspects the field that has the invalid sign can be executed when a
program check occurs. For exampie, when an invalid sign results from
packing an entirely blank field, the sign can be corrected by
programodng, and transaction deletion or program termination is avoided.
The second alteration concerns the recognition of a storage
protection exception during the execution of an EDIT or an EDIT AND MARK
instruction. On a Model 145 a protection exception always occurs when a
pattern character is fetched from a location protected for storing but
remains unchanged during the edit operation. This change eliminates
unpredictable system operation during editing on a Model 145. The
occurrence of a protection exception for the situation described is
model dependent for System/360 models.
INTERVAL TIMER
The interval timer at decimal location 80 in the fixed processor
storage area is a standard feature and has a resolution of 3.33 ms
instead of the 16.6-ms resolution implemented for the timer on Models 30
and 40. Its maximum time period remains 15.5 hours. The higher
resolution of this interval timer eliminates many of the problems
encountered in accounting routine accuracy caused by task execution
durations that are shorter than the 16.6-ms resolution interval.
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A Guide to the IBM System/370 Model 145