Method and operating system for executing programs in a multi-mode microprocessor

• US 5,027,273 A
• Filed: 04/21/1989
• Issued: 06/25/1991
• Est. Priority Date: 04/10/1985
• Status: Expired due to Term

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Letwin, James
• Primary Examiner(s): Fleming, Michael R.
• Assistant Examiner(s): CHUN, DEBRA
• Application Number:
  US07/341,567
• Time in Patent Office: 795 Days
• Field of Search: 364/200, 364/900
• US Class Current: 713/600
• CPC Class Codes: G06F 1/24 Resetting means
• CPC Class Codes: G06F 12/0292 using tables or multilevel address translation means G06F12/023 takes precedence; address translation in virtual memory systems G06F12/10
• CPC Class Codes: G06F 9/45533 Hypervisors; Virtual machine monitors
• CPC Class Codes: G06F 9/468 Specific access rights for resources, e.g. using capability register
• CPC Class Codes: G06F 9/4812 by interrupt, e.g. masked

Abstract

Improved methods and operating systems for use with a multi-mode microprocessor enable efficient operation in a multi-mode environment. Preferred embodiments for use with microprocessors which were not designed to switch from each mode to another mode enable multi-tasking of a mixture of programs written for different modes using the mode switching methods of the present invention. Frequently used portions of the operating system are stored in memory at locations which can be commonly addressed in all modes. Means for handling device drivers and interrupts in all modes are also provided. Preferred embodiments for use with computer systems using microprocessors such as the Intel 80286 include means for storing the operating system routines to maximize performance of the system in real mode. Auxiliary protection hardware and I/O masking hardware are also provided in alternate preferred embodiments to enhance protection during real mode operation of such systems. Means for handling interrupts in a mode switching environment and alternate embodiments to eliminate problems caused by hooking programs in a multi-tasking environment are also provided.

Claims

1. A method for accessing a segment in a multi-mode computer having segmented addressing, the computer having a memory, the computer having a segment selector to select the segment, the segment having a base address, the computer having a first mode wherein the base address of the segment is addressed by the segment selector and a second mode wherein the base address of the segment is addressed indirectly by the segment selector which points to a memory location within a mapping system where the base address of the segment is stored, the method allowing the segment to be accessed by the same segment selector value in both the first and second modes, the method comprising the steps of:

(a) selecting an address that is a multiple of 16 to be the base address of the segment;

(b) when the computer is in either the first mode or the second mode,

(1) setting the segment selector to a value so that the segment selector addresses the base address of the segment when the computer is in the first mode;

(2) storing at a selected memory location within the mapping system the base address of the segment, the memory location being selected so that it is pointed to by the segment selector as set in step (1) when the computer is in the second mode; and

(3) loading the segment into the memory at the base address; and

(c) accessing the segment in both the first and second modes using the segment selector.

2. The method of claim 1 wherein the segment contains program routines.

3. The method of claim 1 wherein the segment contains operating system routines.

4. The method of claim 1 wherein the base address in step (a) is set to a value that is greater than or equal to 128.

5. The method of claim 4 wherein the segment contains program routines.

6. The method of claim 4 wherein the segment contains operating system routines.

7. The method of claim 1 wherein the base address in step (a) is set to a value that is a multiple of 128.

8. The method of claim 7 wherein the segment contains program routines.

9. The method of claim 7 wherein the segment contains operating system routines.

10. A method for accessing a segment in a computer, the computer having a memory and the computer based on an Intel 80286 or compatible microprocessor, the microprocessor having segmented addressing and a segment selector to select the segment, the segment having a base address, the microprocessor having a real mode wherein the base address of the segment is addressed by the segment selector and a protected mode wherein the base address of the segment is addressed indirectly by the segment selector which points to a memory location within a descriptor table where the base address of the segment is stored, the method allowing the segment to be accessed by the same segment selector value in both the real and protected modes, the method comprising the steps of:

(a) selecting an address that is a multiple of 16 to be the base address of the segment;

(b) when the computer is in either the real mode or the protected mode,

(1) setting the segment selector to a value so that the segment selector addresses the base address of the segment when the computer is in the real mode;

(2) storing at a selected memory location within the descriptor table the base address of the segment, the memory location being selected so that it is pointed to by the segment selector as set in step (1) when the computer is in the protected mode; and

(3) loading the segment into the memory at the base address; and

(c) accessing the segment in both the real and protected modes using the segment selector.

11. The method of claim 10 wherein the segment contains program routines.

12. The method of claim 10 wherein the segment contains operating system routines.

13. The method of claim 10 wherein the descriptor table is the local descriptor table.

14. The method of claim 13 wherein the segment contains program routines.

15. The method of claim 13 wherein the segment contains operating system routines.

16. The method of claim 10 wherein the descriptor table is a global descriptor table.

17. The method of claim 16 wherein the base address in step (a) is set to a value that is a multiple of 128.

18. The method of claim 17 wherein the segment contains program routines.

19. The method of claim 17 wherein the segment contains operating system routines.

20. The method of claim 16 wherein the segment contains program routines.

21. The method of claim 16 wherein the segment contains operating system routines.