HP 64783A, User Manual

Page: 187 / 816

vector, the emulator attempts to read from the address it points to. If the read
succeeds, the emulator single steps without modifying the vector table. Otherwise,
the emulator attempts to write the current value of VBR into the trace exception
vector (because the vector table is readable).
There are some limitations when single stepping. A step may fail when single
stepping an instruction that changes the address of the vector table (modifies the
VBR register). With the background monitor, instructions that can be interrupted
(ie: floating-point operations) may not complete because the emulator generates an
interrupt after a finite amount of time after the single step is initiated.
Examples
To step the processor one instruction from its present location, choose
Execution
→
Step Instruction
→
from PC, or on the command line, enter:
step
To step the processor three instructions from the current program counter:
step 3
To step the processor five source-level instructions from the init_system symbol in
the demo program:
step 5 source from init_system
To step once from the program entry point, choose
Execution
→
Step Instruction
→
from Transfer Address, or on the command line,
enter:
step from transfer_address
Chapter 4: Using the Emulator
Using Processor Run Controls
157