Emc Corporation

Edde Tin-Shek Tang

William A Brant

Michael Edward Nielson

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.

Address protection circuit and method for preventing access to

Data in a system having dynamic random access memories (DRAM's) is preserved despite loss of the primary source of electrical power to that system. A Flash RAM and a small auxiliary power source are employed by a controller independent of the system to transfer the DRAM contents to the Flash RAM immediately upon loss of primary system power. The data is also automatically returned to the DRAM after return of primary power with special data signals or sequences being utilized in a multiple controller environment so as to award the complete data recovery function to the first controller to demand attention.

Growing community of inventors

Boulder, CO, United States of America

Edde Tin-Shek Tang