 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] SMS: B26015      ]
 ] LEMUEL GRADY       ]    BFS PROGRAM NOTE         ] DR: 109639       ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE (X)  USER NOTE ( ) ] DATE:            ]
 ] RID/(310) 922-0128 ]      RELEASE NOTE ( )       ]       6/13/95    ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ]   OI23 AND SUBS               ]  CREW (X)  GROUND (X)  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]           MAJOR SOFTWARE AREA:            ] OPS MODES AFFECTED:     ]
 ]BSL(X) BSS( ) GNC( ) SEQ( ) SM/SP( ) IPL( )]         N/A             ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA:     MCDS INTERFACE                               ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS:   MG018101 / 3.2.2.1 & 3.2.1.1.2               ]
 ]_____________________________________________________________________]
 ] TITLE:                                                              ]
 ]                     BSL DEU POLL REQUEST ANOMALY                    ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ]                                                                     ]
 ]                  SEE SUPPLEMENTAL SHEET                             ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] USER RESPONSE:                                                      ]
 ]                                                                     ]
 ] 1. IF A "NO DEU RESPONSE" MESSAGE IS DISPLAYED ON THE DEU,          ]
 ]    ACKNOWLEDGE THE MESSAGE BY PRESSING THE DEU KEYBOARD             ]
 ]    'MSG RESET' KEY.                                                 ]
 ]                                                                     ]
 ] 2. VERIFY THE NEXT MESSAGE IS THE BFS LOADED MESSAGE.               ]
 ]                                                                     ]
 ] 3. CONTINUE FOLLOWING THE REMAINING BFS LOAD PROCEDURES.            ]
 ]                                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]RI: <S> G. ALBRIGHT       DATE 06/28/95]                             ]
 ]    --------------------      ---------]                             ]
 ]ASD:  ERIC C. BINGHAM     DATE 07/12/95]                             ]
 ]    --------------------      ---------] DARRELL E. STAMPER 07/14/95 ]
 ]PF MGR: DAVID STEPHENSON  DATE 07/13/95]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_____________________________________________________________________]
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 +_____________________________________________________________________
 ]                                                                     ]
 ]                       SUPPLEMENTAL SHEET                            ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] AUTHOR:            ]                             ] SMS: B26015      ]
 ] LEMUEL GRADY       ]    BFS PROGRAM NOTE         ] DR: 109639       ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE (X)  USER NOTE ( ) ] DATE:            ]
 ] RID/(310) 922-0128 ]      RELEASE NOTE ( )       ]       6/13/95    ]
 ]____________________]_____________________________]__________________]
 ] TITLE:                                                              ]
 ]                  BSL DEU POLL REQUEST ANOMALY                       ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ]                                                                     ]
 ] ANALYSIS HAS SHOWN THAT A TIMING ANOMALY EXISTS IN SCHEDULING AND   ]
 ] IN PERFORMING DEU I/O REQUESTS.  THIS ANOMALY IS CAPABLE OF         ]
 ] PRODUCING A SMALL TIMING WINDOW THAT MAY CAUSE AN ERRONEOUS FAULT   ]
 ] MESSAGE "NO DEU RESPONSE" TO BE DISPLAYED.  THIS ANOMALY OCCURS     ]
 ] WHEN THE IOP IS SET BUSY FOR THE PURPOSE OF READING THE BFS FROM    ]
 ] THE MMU.  WHEN A BLOCK OF DATA IS READ INTO GPC MEMORY, THE CPU IS  ]
 ] NOTIFIED BY THE IOP VIA AN EXTERNAL-2 INTERRUPT, TO BEGIN           ]
 ] CHECKSUMING THE BLOCK OF DATA THAT WAS JUST LOADED WHILE THE NEXT   ]
 ] BLOCK OF DATA IS BEING READ BY THE IOP INTO GPC MEMORY.  THIS LOAD  ]
 ] PROCESS CONTINUES UNTIL THE BFS LOAD IS COMPLETED.  THIS LOAD       ]
 ] PROCESS ALSO KEEPS THE IOP AND CPU BUSY FOR LONG TIME PERIODS       ]
 ] DURING A MINOR CYCLE.  THE PROCESS OF CHECKSUMING EACH BLOCK OF     ]
 ] DATA THAT IS LOADED INTO THE GPC'S MEMORY BY THE IOP IS A PRIORITY  ]
 ] TASK.  THIS TASK USES A LARGE AMOUNT OF THE CURRENT MINOR CYCLE'S   ]
 ] TIME WHICH MAY PREVENT DEU I/O REQUEST TASK FOR THAT MINOR CYCLE    ]
 ] FROM BEING SCHEDULED FOR THAT MINOR CYCLE. THE DEU I/O REQUEST TASK ]
 ] IS REQUIRED TO POLL THE DEU TWICE A SECOND.  THE PROCESS OF READING ]
 ] BFS FROM THE MMU BY THE IOP IS AN ASYNCHRONOUS TASK.  THIS TASK WILL]
 ] ALSO KEEP THE IOP BUSY FOR LONG TIME INTERVALS.  THEREFORE, IN ORDER]
 ] FOR THE CPU TO SCHEDULE ANY I/O WHEN THE IOP IS BUSY, AN INTER      ]
 ] PROCESS VARIABLE (IPV) BSL2CNTL IS USED.  THIS VARIABLE IS SET BY   ]
 ] THE CPU AND IS CHECKED BY THE IOP.  WHEN THE IOP DETECTS THE        ]
 ] VARIABLE BSL2CNTL SET TO A NON-ZERO VALUE, THE DEU I/O REQUEST IS   ]
 ] PERFORMED. THIS HANDSHAKING INTERFACE IS PERFORMED ONLY WHEN THE    ]
 ] IOP IS PERFORMING A MMU READ OPERATION.   THIS ANOMALY OCCURS WHEN  ]
 ] THE IOP IS KEPT BUSY DURING A MMU READ OPERATION, AND MISSES        ]
 ] CHECKING THE IPV.  THEREFORE, THE IOP DOES NOT PERFORM THE          ]
 ] REQUESTED DEU I/O (DEU).  WHEN THIS OCCURS, A "NO DEU RESPONSE"     ]
 ] MESSAGE IS DISPLAYED.                                               ]
 ] ____________________________________________________________________]
 ] USER RESPONSE:                                                      ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
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