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The principle of fault tolerance in the redundant processor modules is based on continuous
updating of the backup unit to the same status as the primary unit. This enables the backup unit
to assume control without affecting surrounding systems in a bumpless manner.
This principle involves dynamic division of the program execution into execution units and the
creation of rollback points at which the processor module’s status is completely defined.
In this context, the processor module’s total status is defined as the processor module’s internal
status, that is, the contents of the processor registers, plus the contents of the data memory.
The backup unit’s status is updated each time the primary unit passes a rollback point, enabling
the backup unit to resume program execution from the last rollback point passed, should the
primary unit fail due to error.
In order to minimize the amount of information involved in the update, the backup unit is
updated only with the changes taking place since the latest rollback point.
Between rollback points, these changes that writes in the data memory, are stored in a log buffer
in the backup unit. At a rollback point, the processor’s total register contents are also written
into the data memory, so that this information is also logged. Once the rollback point is
established, the logged write operations are transferred to the backup unit’s data memory.
If the primary unit fails because of an error, the backup unit resumes execution from the last
rollback point, which means the last execution unit is partially re-executed by the backup unit.
In order to re-execute a portion of the execution unit without affecting the peripheral units (I/O
and communication units), the peripheral units’ references are also logged between rollback
points. During re-execution, the results of the peripheral units’ references, which have already
been executed, are used, rather than re-executing them. The results of read operations are
retrieved from the log, and write operations pass without execution, since they have already
been executed. The peripheral units’ statuses, then, are not affected by the re-execution in any
way, except for the time delay which occurs.
The RAM included in the processor module provides automatic error detection and error
correction.
•
If one bit becomes incorrect in a storage location, this is corrected automatically. If the
error repeats, a system message is sent to warn that the memory is about to become
defective.
•
If two bits become incorrect in a storage location, the system changes over to the backup
unit.
Содержание Advant Controller 450
Страница 1: ...Advant OCS with Master software GYDQW RQWUROOHU User s Guide 3BSE 002 415R701 Rev A ...
Страница 26: ...Advant Controller 450 User s Guide Table of Contents 3BSE 002 415R701 Rev A xvi ...
Страница 30: ...Advant Controller 450 User s Guide Table of Contents 3BSE 002 415R701 Rev A xx ...
Страница 488: ... GYDQW RQWUROOHU 8VHU V XLGH SSHQGL DUGZDUH 0RGXOHV A 48 3BSE 002 415R701 Rev A ...
Страница 496: ...Advant Controller 450 User s Guide Appendix C Delivery Documentation C 2 3BSE 002 415R701 Rev A ...
Страница 508: ...Advant Controller 450 User s Guide Appendix D Item Designations D 12 3BSE 002 415R701 Rev A ...
Страница 514: ...Advant Controller 450 User s Guide Appendix E Current Consumption and Heat Dissipation E 6 3BSE 002 415R701 Rev A ...
Страница 518: ...Advant Controller 450 User s Guide Appendix F Load Calculation F 4 3BSE 002 415R701 Rev A ...
Страница 522: ...Advant Controller 450 User s Guide Appendix G Memory Calculation G 4 3BSE 002 415R701 Rev A ...
Страница 528: ...Advant Controller 450 User s Guide Appendix H Halt Codes H 6 3BSE 002 415R701 Rev A ...
Страница 561: ...Advant Controller 450 User s Guide Index 3BSE 002 415R701 Rev A iii V Valve control 1 102 VT100 terminal 1 105 ...
Страница 562: ...Advant Controller 450 User s Guide Index iv 3BSE 002 415R701 Rev A ...
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Страница 564: ...3BSE 002 415R701 Rev A March 2000 ...