Polling of I/O device status comparison performed in the polled I/O device
First Claim
1. A method for a central processing unit (CPU) to obtain from an input/output (I/O) device the contents of a status register therein indicating the status thereof, comprising the steps of:
- transferring from said CPU to said I/O device expected status data corresponding to a predetermined status to be attained by said I/O device upon the occurrence of an expected event;
storing said expected status data in a match register in said I/O device for use during a subsequent polling operation;
issuing from said CPU to said I/O device a request to read said status register as part of said polling operation;
comparing the contents of said status register to the contents of said match register to determine whether said event has occurred, the occurrence of said event being indicated by a match therebetween; and
returning the contents of said status register to said CPU in response to said request upon an indication of a match in said comparing step.
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Accused Products
Abstract
A method and apparatus for polling a status register selectively delays the returning of status data in the status register. Prior to polling, a match register is loaded via a system bus with a desired status. Status data is presented to the system bus when the status data is the same as the desired status. The features of the invention also permit the masking of selective bits of the status register during the comparison of the status data with the desired status. A mode register selectively inhibits the delayed presentation, and a timer ensures that status data is presented to the system bus within a predetermined interval even if the status data is not the same as the desired status.
87 Citations
8 Claims
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1. A method for a central processing unit (CPU) to obtain from an input/output (I/O) device the contents of a status register therein indicating the status thereof, comprising the steps of:
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transferring from said CPU to said I/O device expected status data corresponding to a predetermined status to be attained by said I/O device upon the occurrence of an expected event; storing said expected status data in a match register in said I/O device for use during a subsequent polling operation; issuing from said CPU to said I/O device a request to read said status register as part of said polling operation; comparing the contents of said status register to the contents of said match register to determine whether said event has occurred, the occurrence of said event being indicated by a match therebetween; and returning the contents of said status register to said CPU in response to said request upon an indication of a match in said comparing step. - View Dependent Claims (2, 3, 4)
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5. A computer system, comprising:
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a central processing unit (CPU); a status register coupled to said CPU whose contents indicate the status of an associated input/output (I/O) device to be polled by said CPU; a match register coupled to said CPU to be written therefrom with expected status data corresponding to a predetermined status to be attained by said I/O device upon the occurrence of an expected event; a comparator coupled to said status register and said match register to indicate whether the contents thereof match; means for receiving from said CPU a request to read said status register to determine whether said event has occurred; and means for returning the contents of said status register to said CPU in response to said request upon an indication of a match by said comparator. - View Dependent Claims (6, 7, 8)
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Specification