Texas Instruments 990 Operation Manual page 107

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3.6.2.3 Excluding Loops from Instruction Traces. When tracing a program with printout, it is
sometimes desirable to exclude printing of small loops which are very frequently executed or
which run for many iterations. (See figure 3-1.) These may be excluded by carefully choosing
trace regions, which are areas where an instruction trace
is
to be run within a program. In
determining which trace region is applicable (and thus what trace type to use), the system will
find the first (lowest numbered) region containing the user's PC. By selecting a high numbered
trace (3) for the main trace control and then setting regions within that large region with lower
numbered traces which do not print, the user may prevent a large quantity of output where it is
not wanted.
An alternate mechanism is to allow the small loops to be executed by SIE and the remaining
prQgram traced. (See figure 3-2.) This can be done by setting trace regions to cover all of the
program except the small loops or frequently executed parts. Such a mechanism works well
unless the user
is
using XOPs (other than XOP 15 for PX9MTP I/O) or interrupts which are
processed differently by SIE and instruction trace.
If the user is performing I/O by means of supervisor calls (XOP 15) to PX9MTP, this XOP is
executed directly (without SIE or instruction trace). If XOP 15 is not used for program I/O,
it is not executed directly under SIE.
USER PROGRAM
PGM~
A:
JMP A
a:
(A)133102
TRACE REGION
DEFINITION
TRACE
REGION 3
}
TRACE
REGION 2
}
}
CONTROLLING
TRACE REGION
, REGION 3
REGION 2
REGION 3
Figure 3-1. Trace Region'Precedence of Lower Region Number
3-69
Digital Systems Division .