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Nested Error Recoveries

IP.com Disclosure Number: IPCOM000051866D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Videki, ER: AUTHOR

Abstract

Many peripheral subsystems require host intervention for recovery from device errors and control unit errors. In a control unit having a data buffer, the operation of the devices and the operation of the processes in the host may be highly asynchronous; therefore, the timing of any error interrupt may or may not have an operational relationship between the reporting of the error and the execution of the process. Further, a plurality of errors may occur before an error recovery has been abandoned or successfully completed.

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Nested Error Recoveries

Many peripheral subsystems require host intervention for recovery from device errors and control unit errors. In a control unit having a data buffer, the operation of the devices and the operation of the processes in the host may be highly asynchronous; therefore, the timing of any error interrupt may or may not have an operational relationship between the reporting of the error and the execution of the process. Further, a plurality of errors may occur before an error recovery has been abandoned or successfully completed.

For example, a first error can be a device error. The error is reported, and the host supplies a sense command to the control unit for fetching the error- related data. The host then invokes an ERP (Error Recovery Procedure)- based upon the error reported. For completion of the ERP, a second error occurs. This error is a control-unit- or device-control-related error. The ERP is interrupted, with the data saved from the sense command being preserved within the host.

The host then sends a second sense command to the control unit for analyzing the second error. Since it is a control error, recovery from the device error cannot proceed until the control error has been solved. Accordingly, the control error is solved and then the host automatically returns to the ERP-1 using the data saved with respect to the device error.

The occurrence of the second error interrupt from the control unit may occur at any time. For example, it...