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VM/SP Overlapped I/O With Error Recovery

IP.com Disclosure Number: IPCOM000060986D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Foreman, DJ: AUTHOR [+2]

Abstract

The implementation of a small set of changes to three program modules, and one macro of the CP portion of VM/SP that achieves overlapped I/O with error detection/correction for disk, tape, and unit record devices, is accomplished without introducing new media formats. The one macro changed is IOBLOK to provide a bit to indicate that the I/O operation involves overlapped I/O with error correction, and to provide an assembler language EQU statement to indicate an IOBLOK that is 8 bytes larger than other versions of the IOBLOK, for storing the virtual device address across the overlapped I/O and error recovery. The module DMKGIO (entered via DIAG-20) is changed to examine the channel command word (CCW) register for an odd value. In past environments this would represent an error.

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VM/SP Overlapped I/O With Error Recovery

The implementation of a small set of changes to three program modules, and one macro of the CP portion of VM/SP that achieves overlapped I/O with error detection/correction for disk, tape, and unit record devices, is accomplished without introducing new media formats. The one macro changed is IOBLOK to provide a bit to indicate that the I/O operation involves overlapped I/O with error correction, and to provide an assembler language EQU statement to indicate an IOBLOK that is 8 bytes larger than other versions of the IOBLOK, for storing the virtual device address across the overlapped I/O and error recovery. The module DMKGIO (entered via DIAG-20) is changed to examine the channel command word (CCW) register for an odd value. In past environments this would represent an error. The odd value in the register is an indicator that the I/O request is for overlapped I/O. For this case the virtual machine's channel address word (CAW) is examined for the CCW address of the I/O operation. The CAW must differ from the register by 1, and be a proper value. DMKVSI is called to build the IOBLOK for the I/O operation, and set the interrupt vector for the completion of the operation. The remaining operations of DMKGIO are unchanged. DMKVSI creates an extended IOBLOK, saves the virtual machine's virtual device address, builds the translated CCW chain, and sets the indicators for overlapped I/O with error recovery. The interrupt vector of...