Abstract

In a multi-tasking computing system environment, one program is halted and context switched out so that a processor may context switch in a subsequent program for execution. Processor state information exists which reflects the state of the program being context switched out. Storage of this processor state information permits successful resumption of the context switched out program. When the context switched out program is subsequently context switched in, the stored processor information is loaded in preparation for successfully resuming the program at the point in which execution was previously halted. Although, large areas of memory can be allocated to processor state information storage, only a portion of this may need to be preserved across a context switch for successfully saving and resuming the context switched out program. Unnecessarily saving and loading all available processor state information can be noticeably inefficient particularly where relatively large amounts of processor state information exists. In one embodiment, a processor requests a co-processor to context switch out the currently executing program. At a predetermined appropriate point in the executing program, the co-processor responds by halting program execution and saving only the minimal amount of processor state information necessary for successful restoration of the program. The appropriate point is chosen by the application programmer at a location in the executing program that requires preserving a minimal portion of the processor information across a context switch. By saving only a minimal amount of processor information, processor time savings are accumulated across context save and restoration operations.

Other References

• Motorola Inc.,MC68881/MC68882 Use's Manual; p. 6-27, section 6.4.1, 1987
• Borland, Turbo Debugger, version 4.5, User's Guide, Borland International, pp. 67-74, 199