Intel ARCHITECTURE IA-32 User Manual Page 62

  • Download
  • Add to my manuals
  • Print
  • Page
    / 636
  • Table of contents
  • BOOKMARKS
  • Rated. / 5. Based on customer reviews
Page view 61
2-14 Vol. 3A
SYSTEM ARCHITECTURE OVERVIEW
VIF Virtual Interrupt (bit 19) — Contains a virtual image of the IF flag. This flag is used
in conjunction with the VIP flag. The processor only recognizes the VIF flag when
either the VME flag or the PVI flag in control register CR4 is set and the IOPL is less
than 3. (The VME flag enables the virtual-8086 mode extensions; the PVI flag enables
the protected-mode virtual interrupts.)
See also: Section 15.3.3.5, “Method 6: Software Interrupt Handling,” and Section 15.4,
“Protected-Mode Virtual Interrupts.”
VIP Virtual interrupt pending (bit 20) — Set by software to indicate that an interrupt is
pending; cleared to indicate that no interrupt is pending. This flag is used in conjunction
with the VIF flag. The processor reads this flag but never modifies it. The processor
only recognizes the VIP flag when either the VME flag or the PVI flag in control
register CR4 is set and the IOPL is less than 3. The VME flag enables the virtual-8086
mode extensions; the PVI flag enables the protected-mode virtual interrupts.
See Section 15.3.3.5, “Method 6: Software Interrupt Handling,” and Section 15.4,
“Protected-Mode Virtual Interrupts.”
ID Identification (bit 21). — The ability of a program or procedure to set or clear this flag
indicates support for the CPUID instruction.
2.3.1 System Flags and Fields in IA-32e Mode
In 64-bit mode, the RFLAGS register expands to 64 bits with the upper 32 bits reserved. System
flags in RFLAGS (64-bit mode) or EFLAGS (compatibility mode) are shown in Figure 2-4.
In IA-32e mode, the processor does not allow the VM bit to be set because virtual-8086 mode
is not supported (attempts to set the bit are ignored). Also, the processor will not set the NT bit.
The processor does, however, allow software to set the NT bit (note that an IRET causes a
general protection fault in IA-32e mode if the NT bit is set).
In IA-32e mode, the SYSCALL/SYSRET instructions have a programmable method of speci-
fying which bits are cleared in RFLAGS/EFLAGS. These instructions save/restore
EFLAGS/RFLAGS.
2.4 MEMORY-MANAGEMENT REGISTERS
The processor provides four memory-management registers (GDTR, LDTR, IDTR, and TR)
that specify the locations of the data structures which control segmented memory management
(see Figure 2-5). Special instructions are provided for loading and storing these registers.
Page view 61
1 2 ... 57 58 59 60 61 62 63 64 65 66 67 ... 635 636

Comments to this Manuals

No comments