HP 64783A, Руководство пользователя

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When displaying memory mnemonic, a highlighted bar shows the current program
counter address. After each step, the highlighted bar moves to the new PC address.
When displaying registers, the registers are updated after every step.
You can open multiple windows to show memory mnemonic and registers at the
same time. Both are updated with each step.
If you omit the <address>, the current program counter value is used. You can use
transfer_address to step from the entry point of the program.
When stepping through instructions associated with source lines, execution may
take a long time and the message "Stepping source line 1; Next PC: <address>" is
displayed on the status line. In this situation, you can abort the step command by
pressing <CTRL>c.
The emulator uses the built-in tracing capability of the MC68040 processor to
single step assembly instructions. The emulator needs the trace exception vector
(located at offset 0x24 in the vector table) to be set properly in order to single step
instructions. When a step command is given to the emulator, the emulator reads the
trace exception vector and attempts to change one or more vector table entries if the
trace exception vector is not set correctly. As long as the vector table is located in
emulation memory or target RAM, stepping should always succeed. Upon
completion of single stepping, the emulator restores modified vector table entries
and issues a status message the first time the vector table is modified.
If the trace exception vector does not contain the correct value and the vector table
is located in target ROM, the emulator will issue an error message and not perform
the single step. There are two ways to deal with this situation. Either alter the
ROM-based code so the trace vector contains the correct value, or copy/relocate the
vector table into emulation memory or target RAM.
The correct value of the trace exception vector differs, depending on whether you
are using a background or foreground monitor. The foreground monitor requires
that the trace exception vector point to the TRACE_ENTRY address in the monitor
(located at offset 0x680 from the start of the monitor). If the trace exception vector
already contains the correct value, the emulator performs the single step without
modifying the vector table. Otherwise, the emulator attempts to change the trace
a-line and f-line exception vectors to the TRACE_ENTRY address in the
foreground monitor.
The background monitor only requires that the trace exception vector be an even
value and point to readable memory. This allows the processor to complete trace
exception processing, including initial prefetches from the trace exception handler,
during transition into the background monitor. After reading the trace exception
Chapter 4: Using the Emulator
Using Processor Run Controls
156