Method and apparatus for switching between the modes of a processor

In a computer system including a processor operable in a first mode and a second mode, said processor being coupled to a storage device, a method for switching between said first mode and said second mode of said processor, said method comprising the steps of:

• A) storing, in response to a first interrupt, a first information in said storage device for switching to said first mode to process a first routine, wherein said first routine is stored in said storage device;
• B) switching from processing a second routine in said first mode to processing a third routine in said second mode in response to a second interrupt occurring subsequent to said step of storing said first information, wherein said second routine and said third routine are stored in said storage device;
• C) storing, in response to said second interrupt, a second information in said storage device for resuming processing of said second routine in said first mode;
• and
• D) switching from said second mode to said first mode to process said first routine using said first information if processing said first routine is required, said switching in step D occurring in response to said switching in step B.

A method for transitioning between modes of a processor, said method comprising the computer implemented steps of:

• storing a first return information for returning to execution at a first location in a normal operating mode in response to performing a first transition from the normal operating mode to a different operating mode;
• returning to the normal operating mode from the first transition;
• performing a second transition from executing at a second location in the normal operating mode to the different operating mode;
• and
• returning to the normal operating mode from the second transition using the first return information.

In a computer system having a processor operable in at least a first and second mode, said second mode having a first memory area reserved for storing data used to return to said first mode, a method comprising the computer implemented steps of:

• storing in a second memory area a first return information for returning to execution at a first location in said first mode in response to performing a first transition from the first mode to the second mode;
• returning to the first mode from the first transition using data in said first memory area;
• performing a second transition from executing at a second location in the first mode to the second mode;
• copying said first return information from said second memory area into said first memory area;
• and
• returning to the first mode from the second transition using the first return information.

A computer system comprising:

• a processor that in response one type of interrupt transitions from a first mode to a second mode and stores return information in a first memory area for resuming execution in said first mode, wherein said first memory area is reserved for storing data for transitioning back to said first mode;
• and
• a storage device coupled to said processor having stored therein a plurality of instructions embodying the logic for causing the processor to,
• store in a second memory area a first return information for returning to execution at a first location in said first mode in response to performing a first transition from the first mode to the second mode;
• return to the first mode from the first transition;
• copy the first return information from the second memory area into the first memory area in response to performing a second transition from executing at a second location in the first mode to executing in the second mode;
• and
• return to the first mode from the second transition using the first return information.