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US4812968A
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Method for controlling processor access to input/output devices
Assignee: International Business Machines Corp
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Filing: 1986-11-12
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Granted: 1989-03-14
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Expires: 2006-11-12
Abstract
Abstract A method for controlling processor access to input/output control units and devices connected to the control units to prevent control unit and device lookout due to the condition where the channel turn-around time becomes less than the device controller's housekeeping time is disclosed. The problem of control unit and device lockout is overcome by monitoring path and device activity for a given processor while at the same time keeping track of other processors waiting for a given path and device. When it is determined that a given number of consecutive input/output operations have been accomplished for a given processor and at the same time another processor requires this resource, then a busy condition will be asserted for new input/output requests from the current processor for the currently accessed path and/or device. This action forces the offending processor to wait until the controller and/or the device is again available.
Inventors
- 👤 Fred Poole
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 18:24
CPC Classifications
G; G06; G06F; G06F13/00; G06F13/14
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
205 words
A method for controlling processor access to input/output control units, and devices connected to the control units, for each channel input/output request in a shared device multi-processor system comprising for each new input/output request by a processor the steps of: testing for contention of a control unit requested by a processor, and if contention exists for the control unit, determining if a predetermined number of accesses have been made by a current processor having access to the control unit; if a predetermined number of accesses have been made by a current processor having access to the control unit for which there is contention by another processor, signalling the current processor with a busy status to allow access by another processor to the control unit; testing for contention of a device connected to the control unit, and if there is contention determining if a predetermined number of consecutive input/output operations have been performed by a current processor having access to the device; and if a predetermined number of consecutive input/output operations have been performed by the current processor on the device for which there is contention by another processor, signalling the current processor with a busy status to allow access by another processor to the device.
Claim 2
Independent Claim
205 words
A method for controlling processor access to input/output control units, and devices connected to the control units, for each channel input/output request in a shared device multi-processor system comprising for each new input/output request by a processor the steps of: testing for contention of a control unit requested by a processor, and if contention exists for the control unit, determining if a predetermined number of accesses have been made by a current processor having access to the control unit; if a predetermined number of accesses have been made by a current processor having access to the control unit for which there is contention by another processor, signalling the current processor with a busy status to allow access by another processor to the control unit; testing for contention of a device connected to the control unit, and if there is contention determining if a predetermined number of consecutive input/output operations have been performed by a current processor having access to the device; and if a predetermined number of consecutive input/output operations have been performed by the current processor on the device for which there is contention by another processor, signalling the current processor with a busy status to allow access by another processor to the device.
Claim 3
Dependent Claim
93 words
The method for controlling processor access to input/output control units and devices connected to the control units as recited in claim 1 wherein the step of testing for contention of a device comprises the steps of: determining for each channel input/output request if there are other channels which are requesting access to a same device; determining if a current channel request is from a same channel as a last request; counting consecutive accesses by a current channel to an input/output device; and testing a count of consecutive accesses against a predetermined threshold value.
Claim 4
Dependent Claim
122 words
The method for controlling processor access to input/output control units and devices connected to the control units as recited in claim 1 wherein each control unit includes a plurality of paths for allowing access to a plurality of devices connected to the control unit and the step of testing for contention of a control unit comprises the steps of: determining for each channel input/output request if there are other channels which are requesting access to a same path of a control unit; determining if a current channel request is from a same channel as a last request; counting a number of path accesses by a current processor having access to the same path; and testing said count against a predetermined threshold value.
Claim 5
Dependent Claim
208 words
The method for controlling processor access to input/output units and devices connected to the control units as recited in claim 1 wherein each control unit includes a plurality of paths for allowing access to a plurality of devices connected to the control unit and the step of testing for contention of a control unit comprises the steps of: determining for each channel input/output request if there are other channels which are requesting access to a same path of a control unit; determining if a current channel request for a path of a control unit is from a same channel as a last request; counting a number of path accesses by a current processor having access to the path; and testing the count of a number of path accesses against a predetermined threshold value; and wherein the step of testing for contention of a device comprises the steps of: determining for each channel input/output request if there are other channels which are requesting access to a same device; determining if a current channel request for a device is from a same channel as a last request; counting consecutive accesses by a current channel to an input/output device; and testing a count of consecutive accesses against a predetermined threshold value.
Claim 6
Dependent Claim
71 words
The method for controlling processor access to input/output control units and devices as recited in claim 4 wherein if the current channel request for a path in the control unit is not the same as a last path, further comprising the steps of: setting a current path to be the same as a last path; resetting a path usage count; and saving the path usage count and a last path argument.
Claim 7
Dependent Claim
55 words
The method for controlling processor access to input/output control units and devices connected to the control units as recited in claim 4 wherein if a number of path accesses by the current processor has not exceeded said predetermined threshold value, further comprising the step of saving the path usage count and a last path argument.
Claim 8
Dependent Claim
54 words
The method for controlling processor access to input/output control units and devices connected to the control units as recited in claim 4 further comprising, after the step of signalling, the steps of: resetting a last path serviced argument; resetting a device and path usage count; and saving said count and the last path argument.
Claim 9
Dependent Claim
75 words
The method for controlling processor access to input/output control units and devices connected to the control units as recited in claim 4 wherein if a device requested by a channel input/output request is not requested on the same path as a last request for the device, further comprising the steps of: setting a current path as a last path; resetting a device and path usage count; and saving said count and a last path argument.
Claim 10
Dependent Claim
68 words
The method for controlling processor access to input/output control units and devices connected to the control units as recited in claim 4 wherein if for a channel input/output request for a device a number of consecutive accesses by a current channel to the device has not exceeded said predetermined threshold value, then further comprising the step of saving the count of said number and a last path argument.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-03-13 | 1992-09-12 | 1993-03-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-03-13 | 1996-09-12 | 1997-03-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-03-13 | 2000-09-12 | 2001-03-14 | $7700.00 | Window Closed / Lapsed |