 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] DR:              ]
 ]  MONTY QUEENER     ]    PASS PROGRAM NOTE        ]     104798       ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE (X)  USER NOTE ( ) ] DATE:  02/11/91  ]
 ]  IBM/282-7750      ]      RELEASE NOTE( )        ] REV A: 06/10/91  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ]  OI8C THRU OI22               ]  CREW (X)  GROUND (X)  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]        MAJOR SOFTWARE AREA:       ] OPS MODES AFFECTED:             ]
 ]SSW (X)  GNC ( )  VU ( )  SM/PL ( )] G1, G2, G3, G6, G8, G9          ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA: MMU, I/O                                         ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: SDPS                                           ]
 ]_____________________________________________________________________]
 ] TITLE:                                                              ]
 ]        POSSIBLE RS MMU I/O ERROR                                    ]
 ]_____________________________________________________________________]
 ] DESCRIPTION: DUE TO MARGINAL DELAY VALUES IN THE LISTENER BCE PRO-  ]
 ] GRAMS WHICH PERFORM MMU READS, ONE OR MORE RS LISTENER GPCS MAY DE- ]
 ] TECT A COMMAND SYNC I/O ERROR (BCE STAT REG BIT 15=1, IUA=11, AND   ]
 ] POSSIBILITY OF S, E, AND/OR V BIT=1) ON MMU READ TRANSACTIONS.  THIS]
 ] FAILURE OCCURS WHEN AN I/O COMPLETION OCCURS ALMOST SIMULTANEOUSLY  ]
 ] WITH A TIMER INTERRUPT ON WHICH AN MMU TRANSACTION IS INITIATED.    ]
 ] THE ERROR IS MORE LIKELY TO OCCUR IN G9 BECAUSE OF THE UNIQUE G9 I/O]
 ] PROFILE (TIMER AND USER INITIATED).  THE FOLLOWING RS MMU READS ARE ]
 ] EXPOSED TO THIS ERROR:  SSMEC LOADS, G9 TFL/DFL/FPM LOADS, TCS-S    ]
 ] LOADS, AND IMU CHECKPOINT OPERATIONS IN G9 OR G2/G3 (SPEC 21).  IF  ]
 ] THE ERROR OCCURS, ALL RS GPCS TREAT THE TRANSACTION AS FAILED.  THE ]
 ] OPERATION SHOULD BE SUCCESSFUL ON THE USER INITIATED RETRY.  THE    ]
 ] FSP MESSAGE, "I/O ERROR MMU X", IS ANNUNCIATED BY GPCS DETECTING    ]
 ] THE I/O ERROR, IN ADDITION TO ANY APPLICATION S/W ANNUNCIATION, E.G.]
 ] "TFL LOAD FAIL" (ANNUNCIATED BY ALL RS GPCS).                       ]
 ]                                                                     ]
 ] NOTE:  OPS OVERLAYS DO NOT ENCOUNTER THIS PROBLEM DUE TO THE LIMITED]
 ] I/O DURING AN OVERLAY AND THE TIMING OF THE I/O COMPLETIONS.        ]
 ]_____________________________________________________________________]
 ]USER RESPONSE:                                                       ]
 ]                                                                     ]
 ] BE AWARE OF THE ABOVE CONDITION.                                    ]
 ]                                                                     ]
 ] DUE TO THE UNIQUE I/O ERROR SIGNATURE OF THIS ERROR, THE GROUND CAN ]
 ] READILY DISTINGUISH THIS TYPE ANOMALY FROM A REAL MMU PROBLEM.  THE ]
 ] USER SHOULD RETRY THE MMU I/O OPERATION WHICH FAILED.               ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]IBM:  CHARLES HALLIMAN    DATE 07/02/91]                             ]
 ]    --------------------      ---------]                             ]
 ]FDSD:  ROBERT N. HINSON   DATE 07/03/91]                             ]
 ]     -------------------      ---------] DARRELL E. STAMPER 07/08/91 ]
 ]PF MGR:ELIZABETH FOUNTAIN DATE 07/02/91]------------------- -------- ]
 ]       ------------------     ---------] CHAIRMAN, SASCB      DATE   ]
 ]_______________________________________]_____________________________]
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