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Dynamic Determination of System Operation

IP.com Disclosure Number: IPCOM000038597D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Chiang, DL: AUTHOR [+3]

Abstract

A method is described which allows a system to determine how a coprocessor operates by changing the code that will be executed when the coprocessor is reset. The coprocessor card has no ROM (read-only memory) on it. It uses system RAM (random-access memory) or RAM plugged into the system bus. When the processor on the coprocessor card is reset, it begins executing code at segment address X'F000' offset X'FFF0'. As this is in the range of memory that is read/write to the system, the system determines what function the coprocessor performs based on what code is placed in that location. Thus, the operation of the coprocessor system can be dynamically determined at coprocessor start time.

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Dynamic Determination of System Operation

A method is described which allows a system to determine how a coprocessor operates by changing the code that will be executed when the coprocessor is reset. The coprocessor card has no ROM (read-only memory) on it. It uses system RAM (random-access memory) or RAM plugged into the system bus. When the processor on the coprocessor card is reset, it begins executing code at segment address X'F000' offset X'FFF0'. As this is in the range of memory that is read/write to the system, the system determines what function the coprocessor performs based on what code is placed in that location. Thus, the operation of the coprocessor system can be dynamically determined at coprocessor start time. To prevent inadvertent changing of coprocessor system code, the coprocessor card suppresses the WRITE signal to a range (X'E0000' to X'FFFFF') of addresses. Thus, to the coprocessor this memory is read only, while to the system it is read/write. This address range (X'E0000' or X'FFFFF') is reserved by the architecture for system code. The system takes advantage of this fact to put information, needed by coprocessor for the entire duration of the current execution, in tables that cannot be inadvertently or deliberately changed by programs running on the coprocessor. This allows the system to start the coprocessor with tables that appear to the coprocessor to be static (as they are on a PC) but that are really changeable. An example of this ty...