Patent
1997-02-14
1999-01-26
An, Meng-Ai T.
395591, G06F 1300, G06F 1324
Patent
active
058647015
ABSTRACT:
A method and apparatus for handling interrupts after transition of a mask flag is provided. In x86 processors, if the IF flag is cleared, interrupts are to be masked. If the IF flag is set, interrupts are to be handled. However, if the IF flag transitions from a clear state to a set state, and the instruction which sets the IF bit is an STI instruction, then a pending interrupt is to be delayed for one instruction, unless the following instruction is a floating point instruction, and then the interrupt is to be handled immediately. The invention allows an interrupt to cause a branch to an exception handler if the IF bit is set. The exception handler determines whether the prior instruction was an STI instruction, and whether the prior state of the IF bit was clear. If both these conditions are true, the exception handler branches back to the main program. If either condition is not true, the exception handler branches to an interrupt service routine.
REFERENCES:
patent: 4833598 (1989-05-01), Imamura et al.
patent: 5367689 (1994-11-01), Mayer et al.
patent: 5560018 (1996-09-01), Macon, Jr. et al.
patent: 5689720 (1997-11-01), Nguyen et al.
Col Gerard
Henry Glenn
An Meng-Ai T.
Huffman James W.
Integrated Device Technology Inc.
Jean Frantz B.
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