 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] DR:              ]
 ] S. ADAMS           ]    PASS PROGRAM NOTE        ]     25197*       ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE:  JULY 1987 ]
 ] IBM/282-7364       ]      RELEASE NOTE( )        ] REV B: 03/29/91  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ] REL 18 AND SUBS               ]  CREW ( )  GROUND (X)  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]        MAJOR SOFTWARE AREA:       ] OPS MODES AFFECTED:             ]
 ]SSW (X)  GNC ( )  VU (X)  SM/PL ( )] G9                              ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA: DOWNLIST, CYCLE-WRAP                             ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: SDLT, V4.21                                    ]
 ]_____________________________________________________________________]
 ] TITLE:                                                              ]
 ] POSSIBLE DOWNLIST I/O CYCLE WRAP IN G9                              ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:     *DR105668                                          ]
 ]                                                                     ]
 ] DOWNLIST I/O, WHICH IS INITIATED FROM THE SIP TIMER, CAN CYCLE WRAP ]
 ] IF:                                                                 ]
 ]                                                                     ]
 ] A.  SIP OVERRUNS.                                                   ]
 ]                                                                     ]
 ] B.  HIGHER PRIORITY I/O PREVENTS PROCESSING OF THE DOWNLIST I/O     ]
 ]     COMPLETION.                                                     ]
 ]                                                                     ]
 ] A MODE RECALL OR OPS TRANSITION WITH MULTIPLE DEVICES POWERED OFF   ]
 ] OR FAILED CAN CAUSE THE SVC INITIATED MFE INPUT, NSP, AND HDA INPUT ]
 ] TO KEEP THE FLIGHT CRITICAL BUSES BUSY FROM ONE SIP CYCLE TO THE    ]
 ] NEXT, PREVENTING DOWNLIST I/O COMPLETION. ONE DOWNLIST FRAME WILL   ]
 ] BE LOST AND SUBSEQUENT DOWNLIST WILL LOSE "PSEUDO SYNC" UNTIL THE   ]
 ] NEXT OPS TRANSITION. THIS IS A LOW PROBABILITY SCENARIO.            ]
 ]    DOWNLIST I/O COMPLETION MAY ALSO BE HELD OUT DURING THE G9 BFS   ]
 ] ONE-SHOT DATA TRANSFER DUE TO THE HIGHER PRIORITY AND LENGTH OF     ]
 ] THIS I/O TRANSACTION (LENGTH IS APPROX. 20 MSEC).                   ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]USER RESPONSE:                                                       ]
 ]                                                                     ]
 ] NONE.                                                               ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]IBM: PATTI A. THORNTON    DATE 05/07/91]                             ]
 ]    --------------------      ---------]                             ]
 ]FDSD: ROBERT N. HINSON    DATE 05/13/91]                             ]
 ]     -------------------      ---------]DARRELL E. STAMPER  5/15/91  ]
 ]PF MGR: ERIC C. BINGHAM   DATE 05/09/91]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]DNLT:  J. D. BAGWELL      DATE 05/13/91]                             ]
 ]      ------------------      ---------]                             ]
 ]_______________________________________]_____________________________]
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