Electrical computers and digital processing systems: memory – Storage accessing and control – Shared memory area
Patent
1995-10-23
1998-12-08
Gossage, Glenn
Electrical computers and digital processing systems: memory
Storage accessing and control
Shared memory area
711163, 711164, G06F 1214
Patent
active
058484353
ABSTRACT:
An address protection circuit (APC) for cross-checking the integrity of requests to read or write an addressable system memory in a fault-tolerant computer system. In a check mode, the APC checks each address and a source identification code of each memory access request from an address source. The source identification code and current bus address are compared to a range of addresses stored in the APC. If the current bus address is within an "authorized" range, access to that range of locations in the memory is allowed to the address source. If a current memory access request is not authorized, the APC asserts an error signal which may be used to transfer control to a redundant subsystem. The APC contains a content-addressable memory element that can be initialized by a subsystem processor with address ranges and type of access (e.g., read or write) allowed for each source. To enter the setup mode, the APC must first be addressed to switch the APC from its check mode. Thereafter, only a single value in the APC can be changed by the processor. The APC then automatically reverts to its check mode. Further changes to values in the APC each require an explicit switch from the check mode to the setup mode.
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Brant William Alexander
Tang Edde Tin-Shek
Burton, Esq. Carol W.
EMC Corporation
Gossage Glenn
Kubida, Esq. William J.
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