| 摘要 |
A tracer memory (7) stores the history of execution of addresses for the microprogram of an information processing unit to provide clues to the identification of the cause of any exceptional event that may occur in the unit. A pointer register (10) is indexed by one to store in the tracer memory the state of a predetermined group of logical signals at a location designated by the pointer value. When the result of addition to the pointer value surpasses the end address of the tracer memory, the pointer value is changed to the head address of the tracer memory so that data previously written is over written. The tracer memory contains N addresses and on the occurrence of an exceptional event, the current address J in a pointer register is stored in a mask end register 12 and a preceding address I, separated by a predetermined number M of addresses from address J, is stored in a mask start register 11. The value J-M is stored in said mask start register if J-M>0; otherwise, the value {N+(J-M)} is stored. If a second exceptional event occurs during the execution of a failure recovery procedure for the first exceptional event, there is preserved the execution history of the failure recovery procedure caused by the first exceptional event.
|
