Browse Prior Art Database

CPU Mode Switching Method by System Program

IP.com Disclosure Number: IPCOM000104700D
Original Publication Date: 1993-May-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Inui, T: AUTHOR [+3]

Abstract

A program is disclosed that CPU mode switching between the virtual mode and the real mode is made in a system program area which has the same virtual address as the physical address. All data except data required in changing the real mode to virtual mode are stored in a temporal work area belonging to a CPU in the virtual mode.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 75% of the total text.

CPU Mode Switching Method by System Program

      A program is disclosed that CPU mode switching between the
virtual mode and the real mode is made in a system program area which
has the same virtual address as the physical address.  All data
except data required in changing the real mode to virtual mode are
stored in a temporal work area belonging to a CPU in the virtual
mode.

      The Figure shows the CPU state changing from the virtual mode
to the real mode and vice versa.  This switching depends on the
system server managing the CPU virtual mode because the virtual mode
program cannot change itself to the real mode with saving all CPU
register contexts.  Both the system server program and the mode
switching program must be located at the same virtual address as the
physical address to prevent the CPU's instruction pointer from
pointing the bad physical address excluding the proper real mode
program.

      The mode switching program must also save and restore all of
the CPU registers contexts because the CPU real mode is fulfilled by
the CPU reset forcing the register condition to the power-on state.
As for the save and restore work area, the switching program keeps
and uses a temporal work area when it is in the virtual mode and
prevents the real mode program from accessing the work area.  The
only data required by the real mode program in changing the real mode
to the virtual mode are stored in the common work area to be
accessible by the virtual mod...