Intel 253668-032US 사용자 설명서

Vol. 3   17-13

8086 EMULATION

Figure 17-3.  Entering and Leaving Virtual-8086 Mode

Monitor

Virtual-8086

Real Mode

Code

Protected-

Mode Tasks

Virtual-8086

Mode Tasks

(8086

Programs)

Protected-

Mode Interrupt
and Exception

Handlers

Task Switch

1

VM = 1

Protected
Mode

Virtual-8086
Mode

Real-Address
Mode

RESET

PE=1

PE=0 or
RESET

#GP Exception

3

CALL

RET

Task Switch
VM=0

Redirect Interrupt to 8086 Program

Interrupt or Exception Handler

6

IRET

4

Interrupt or
Exception

2

VM = 0

- CALL or JMP where the VM flag in the EFLAGS image is 1.
- IRET where VM is 1 and NT is 1.

4. Normal return from protected-mode interrupt or exception handler.

3. General-protection exception caused by software interrupt (INT n), IRET,

POPF, PUSHF, IN, or OUT when IOPL is less than 3.

2. Hardware interrupt or exception; software interrupt (INT n) when IOPL is 3.

5. A return from the 8086 monitor to redirect an interrupt or exception back

 to an interrupt or exception handler in the 8086 program running in virtual-

6. Internal redirection of a software interrupt (INT n) when VME is 1,

IOPL is <3, and the redirection bit is 1.

IRET

5

8086 mode.

1. Task switch carried out in either of two ways: