Texas Instruments 990 Operation Manual page 108

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945255-9701
USER PROGRAM
PGM:
A:
JMP A
B:
(A)133103
}
TRACE REGION
DEFINITION
TRACE
REGION 1
NO TRACE
REGION
TRACE
REGION 2
Figure 3-2. Using Both Trace and SIE
}
MODE OF
EXECUTION
TRACE
SIE
TRACE
3.6.2.4 Simulating an Interrupt. A BLWP instruction may be used to control an interrupt
routine which is being checked out. This can be handled with the following code sequence:
Instruction
Operand
LIMI
INTLVL
BLWP
@INTLVL*4
JMP
$
Generated Code
0300
0420
4*i
IOFF
The LIMI sets the interrupt status to the correct level. The BLWP transfers control through the
interrupt vector. The quantity i is the value to which INTLVL is equated.
3.6.3 PATCHING. Patching (attaching portions of code to existing program code) should be
avoided if possible.
During a debug session, it is generally necessary to make patches to object code; however, it is
advisable never to leave patches in a completed program (or create ROM firmware from a
program with patches). An object program for which there is no corresponding source program is
inconvenient and troublesome.
The following paragraphs cover patching techniques. The examples show how to patch
a
two-address instruction; this instruction is used:
MOV
*Rl,*R2+
3-70
Digital Systems Division