Справочник Пользователя для Intel architecture ia-32
Vol. 3A 15-7
8086 EMULATION
(For backward compatibility to Intel 8086 processors, the default base address and limit of the
interrupt vector table should not be changed.)
interrupt vector table should not be changed.)
Table 15-1 shows the interrupt and exception vectors that can be generated in real-address mode
and virtual-8086 mode, and in the Intel 8086 processor. See Chapter 5, “Interrupt and Exception
Handling”, for a description of the exception conditions.
and virtual-8086 mode, and in the Intel 8086 processor. See Chapter 5, “Interrupt and Exception
Handling”, for a description of the exception conditions.
15.2
VIRTUAL-8086 MODE
Virtual-8086 mode is actually a special type of a task that runs in protected mode. When the
operating-system or executive switches to a virtual-8086-mode task, the processor emulates an
Intel 8086 processor. The execution environment of the processor while in the 8086-emulation
state is the same as is described in Section 15.1, “Real-Address Mode” for real-address mode,
including the extensions. The major difference between the two modes is that in virtual-8086
mode the 8086 emulator uses some protected-mode services (such as the protected-mode inter-
rupt and exception-handling and paging facilities).
operating-system or executive switches to a virtual-8086-mode task, the processor emulates an
Intel 8086 processor. The execution environment of the processor while in the 8086-emulation
state is the same as is described in Section 15.1, “Real-Address Mode” for real-address mode,
including the extensions. The major difference between the two modes is that in virtual-8086
mode the 8086 emulator uses some protected-mode services (such as the protected-mode inter-
rupt and exception-handling and paging facilities).
As in real-address mode, any new or legacy program that has been assembled and/or compiled
to run on an Intel 8086 processor will run in a virtual-8086-mode task. And several 8086
programs can be run as virtual-8086-mode tasks concurrently with normal protected-mode
tasks, using the processor’s multitasking facilities.
to run on an Intel 8086 processor will run in a virtual-8086-mode task. And several 8086
programs can be run as virtual-8086-mode tasks concurrently with normal protected-mode
tasks, using the processor’s multitasking facilities.
Figure 15-2. Interrupt Vector Table in Real-Address Mode
0
2
4
8
12
0
15
Segment Selector
Offset
* Interrupt vector number 0 selects entry 0
Interrupt Vector 0*
Entry 1
Entry 2
Entry 3
Up to Entry 255
IDTR
(called “interrupt vector 0”) in the interrupt
vector table. Interrupt vector 0 in turn
points to the start of the interrupt handler
for interrupt 0.
vector table. Interrupt vector 0 in turn
points to the start of the interrupt handler
for interrupt 0.