Method and apparatus for fully restoring a program context follo

Details Method and apparatus for fully restoring a program context follo Method and apparatus for fully restoring a program context follo

1997-11-07

1999-11-16

Ray, Gopal C.

Electrical computers and digital processing systems: multicomput

Computer-to-computer data routing

Least weight routing

710260, G06F 946

Patent

active

059874953

ABSTRACT:
A method and apparatus for fully restoring the context of a user program, including program status word (PSW) and CPU register contents, following an asynchronous interrupt. Upon the occurrence of an asynchronous interrupt event, control is transferred from the normally executing part of the user program to an interrupt handler of the operating system kernel. The kernel interrupt handler saves the contents of the CPU registers and PSW as they existed at the time of the interrupt in a save area associated with the user program before transferring control to a signal catcher routine of the user program. When it has finished handling the interrupt, the signal catcher routine restores the previous state of program execution as it existed before the interrupt by storing the address of the save area in a selected register (which may be a general register/access register pair), restoring the contents of the registers other than the selected register containing the address of the save area, and then restoring the contents of the PSW and selected register by using a new Resume Program (RP) instruction. The RP instruction contains an operand field specifying through the selected register the base address of the save area together with offset fields specifying the offsets of the saved contents of the PSW and selected register relative to the beginning of the save area. Upon decoding an RP instruction, the CPU executing the instruction adds the displacement to the base address contained in the specified register to form the beginning address of the save area, to which it adds the specified offsets to access the saved PSW and selected register contents. The current PSW and selected register contents are then restored with the saved contents to fully restore the previous program context and return control to the instruction being executed at the point of interrupt. To ensure system integrity, only those fields of the PSW are restored that could have otherwise been restored by a program operating in problem state.

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