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參數(shù)資料
| 型號： | KU386 |
| 廠商： | Intel Corp. |
| 英文描述： | SX MICROPROCESSOR |
| 中文描述： | SX微處理器 |
| 文件頁數(shù)： | 37/102頁 |
| 文件大?。?/td> | 1268K |
| 代理商： | KU386 |
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Intel386
TM
SX MICROPROCESSOR
Several instructions, particularly those applying to
the multitasking and the protection model, are avail-
able only in Protected Mode. Therefore, attempting
to execute the following instructions in Real Mode or
in Virtual 8086 Mode generates an exception 6 fault:
LTR;
LLDT;
LAR;
LSL;
ARPL;
STR;
SLDT;
VERR;
VERW;
The instructions which are IOPL sensitive in Protect-
ed Mode are:
IN;
OUT;
INS;
OUTS;
REP INS;
REP OUTS;
STI;
CLI
In Virtual 8086 Mode the following instructions are
IOPL-sensitive:
INT n;
PUSHF; CLI;
POPF;
STI;
IRET;
The PUSHF, POPF, and IRET instructions are IOPL-
sensitive in Virtual 8086 Mode only. This provision
allows the IF flag to be virtualized to the virtual 8086
Mode program. The INT n software interrupt instruc-
tion is also IOPL-sensitive in Virtual 8086 mode.
Note that the INT 3, INTO, and BOUND instructions
are not IOPL-sensitive in Virtual 8086 Mode.
The I/O instructions that directly refer to addresses
in the processor’s I/O space are IN, INS, OUT, and
OUTS. The Intel386 SX Microprocessor has the abil-
ity to selectively trap references to specific I/O ad-
dresses. The structure that enables selective trap-
ping is the I/O Permission Bit Map in the TSS seg-
ment (see Figures 4.8 and 4.9). The I/O permission
map is a bit vector. The size of the map and its loca-
tion in the TSS segment are variable. The processor
locates the I/O permission map by means of the
I/O
map base
field in the fixed portion of the TSS. The
I/O map base
field is 16 bits wide and contains the
offset of the beginning of the I/O permission map.
In protected mode when an I/O instruction (IN, INS,
OUT or OUTS) is encountered, the processor first
checks whether CPL
s
IOPL. If this condition is true,
the I/O operation may proceed. If not true, the proc-
essor checks the I/O permission map (in Virtual
8086 Mode, the processor consults the map without
regard for the IOPL).
Each bit in the map corresponds to an I/O port byte
address; for example, the bit for port 41 is found at
I/O map base
a
5, bit offset 1. The processor tests
all the bits that correspond to the I/O addresses
spanned by an I/O operation; for example, a double
word operation tests four bits corresponding to four
adjacent byte addresses. If any tested bit is set, the
processor signals a general protection exception. If
all the tested bits are zero, the I/O operations may
proceed.
It is not necessary for the I/O permission map to
represent all the I/O addresses. I/O addresses not
spanned by the map are treated as if they had one-
bits in the map. The
I/O map base
should be at
least one byte less than the TSS limit, the last byte
beyond the I/O mapping information must contain
all 1’s.
Because the I/O permission map is in the TSS seg-
ment, different tasks can have different maps. Thus,
the operating system can allocate ports to a task by
changing the I/O permission map in the task’s TSS.
IMPORTANT IMPLEMENTATION NOTE:
Beyond
the last byte of I/O mapping information in the I/O
permission bit map
must
be a byte containing all 1’s.
The byte of all 1’s must be within the limit of the
Intel386 SX CPU TSS segment (see Figure 4.8).
Interrupt Handling
In order to fully support the emulation of an 8086
machine, interrupts in Virtual 8086 Mode are han-
dled in a unique fashion. When running in Virtual
Mode all interrupts and exceptions involve a privi-
lege change back to the host Intel386 SX Microproc-
essor operating system. The Intel386 SX Microproc-
essor operating system determines if the interrupt
comes from a Protected Mode application or from a
Virtual Mode program by examining the VM bit in the
EFLAGS image stored on the stack.
When a Virtual Mode program is interrupted and ex-
ecution passes to the interrupt routine at level 0, the
VM bit is cleared. However, the VM bit is still set in
the EFLAG image on the stack.
The Intel386 SX Microprocessor operating system in
turn handles the exception or interrupt and then re-
turns control to the 8086 program. The Intel386 SX
Microprocessor operating system may choose to let
the 8086 operating system handle the interrupt or it
may emulate the function of the interrupt handler.
For example, many 8086 operating system calls are
accessed by PUSHing parameters on the stack, and
then executing an INT n instruction. If the IOPL is set
to 0 then all INT n instructions will be intercepted by
the Intel386 SX Microprocessor operating system.
37
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