HP 64783A, User Manual

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never executed because the processor immediately starts interrupt processing. The
interrupt processing proceeds the same as in a normal break.
Before exiting for a step, the monitor checks to make sure that the trace vector is
valid and that it points to accessable memory. If the vector is not even, or if the
memory it points to responds with a bus error or hangs, the emulator temporarily
modifies the trace vector to point to the start of the vector table. Because the
instructions of the trace handler will not be executed, the content of the address
locations is not important.
If the emulator modifies the trace vector, the following status message is given:
!STATUS 155! Vector table modified for single stepping
If the emulator finds it must modify the trace vector for single stepping to complete,
but the modification attempt fails, an error message similar to the following is
displayed:
!ERROR 170! Target bus error: 0ff800024@sd
!ERROR 156! Unable to modify trace vector to ff800000h for single stepping
!ERROR 680! Stepping failed
If this error occurs, the vector table must be modified so that the trace vector
contains an address that points to accessable memory. If the vectors are in ROM,
perhaps the memory can be copied into emulation memory where you can modify it.
One way to watch what the emulator is doing during a step, is to set up the analyzer
to trace only foreground cycles and to store everything. This lets you watch the
emulator check and possibly modify the trace exeception vector. Use the following
commands:
tck -u
tsto any
tg any
t
s
The emulator may experience problems when stepping over instructions that
modify the VBR. This is because the check of the trace exception vector is made
using the old VBR value, but the actual stacking will use the new value of the
VBR. If the new VBR value changes the trace exception vector to something that
would require modification, then stepping can fail.
!ERROR 680! Stepping failed
Chapter 18: Connecting the Emulator to a Target System
Installing Emulator Features
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