Electrical computers and digital processing systems: memory – Storage accessing and control – Control technique
Reexamination Certificate
1999-08-24
2001-11-27
Lane, Jack A. (Department: 2185)
Electrical computers and digital processing systems: memory
Storage accessing and control
Control technique
C711S005000
Reexamination Certificate
active
06324628
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of computer systems. Specifically, the present invention relates to an implementation of a limited access device.
2. Description of the Related Art
To enhance data security in digital processing systems, closed or limited access devices to secure data access have become increasingly popular. Such closed or limited access devices, hereinafter referred to as closed devices, are particularly useful in certain military as well as government applications. A closed device is generally enclosed in a sealed chamber typically formed by metal, composite materials, or chemical coatings that are tamper resistant.
Like a typical digital processing system, a closed device generally contains a plurality of components, such as processor and memory chips. These chips may be mounted on a multi-chip module (“MCM”).
However, once the MCM is sealed in the chamber, it is almost impossible to access the components except through a limited number of I/O (“input and output”) ports. A MCM will not function correctly if data stored in a memory chip is corrupted. Because a sealed MCM is protected from external access, the MCM may have to be disposed of if the data stored in a memory chip of the MCM is corrupted.
SUMMARY OF THE INVENTION
A method and a system for reprogramming a closed device are described. In one embodiment, the system contains an external memory coupled to a closed device. The closed device includes a processor, an internal memory, a select control circuit, an internal data bus, and an external data bus. The internal memory, which is coupled to the processor, is not accessible except through predefined input and output ports of the select control circuit, which are accessible external to the closed device.
The select control circuit selects the external memory as primary memory in response to assertion of a control signal and selects the internal memory as primary memory in response to deassertion of the same control signal. In one embodiment, the primary memory stores programs, such as instructions, machine check handlers, and control code. The internal data bus transports data within the closed device, which includes the internal memory and the select control circuit, and the external data bus transports data between the select control circuit and the external memory.
REFERENCES:
patent: 5237616 (1993-08-01), Abraham et al.
Blakely , Sokoloff, Taylor & Zafman LLP
Lane Jack A.
Trimble Navigation Limited
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