Updating escd nvram
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A computer system for flashing Extended System Configuration Data (ESCD) and associated variables to a flash read-only memory (ROM) is provided.
The contents of the ESCD original buffer or the ESCD sector are compared to the contents of the ESCD runtime buffer.
In addition, a function to read or write ESCD generates a pointer to the size of ESCD for determining an entry point into the ESCD.
A function to read ESCD transfers ESCD from an ESCD area of non-volatile storage to a memory buffer typically having a pointer termed ESCD Buffer, and a function to write ESCD transfers data from the memory buffer to an ESCD area of non-volatile storage.
If a function to read or write ESCD is called from real mode, a segment descriptor is created from a real mode base segment address typically termed a BIOS Selector parameter.
A segment selector serves as a pointer to a segment descriptor for an ESCD area of non-volatile storage.
POST is then exited and the computer system is booted.
During runtime, if a write is performed to ESCD data or an associate variable, the ESCD runtime buffer is updated with the ESCD data or variable provided for the write operation.
ESCD functions are further described in the Extended System Configuration Data Specification, Version 1.02, published on Feb.
14, 1994, by Compaq Computer Corporation, Intel Corporation, and Phoenix Technologies, Ltd.
Option ROM represents a designated area of ROM space which an operating system preferably is programmed not to utilize.
In certain operating modes, however, availability of an option ROM is not guaranteed.
System BIOS code is used by the operating system to read or write ESCD as the non-volatile storage storing ESCD has traditionally resided in the system BIOS memory space.