Updating escd nvram

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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.Accordingly, only system BIOS has known the location of the ESCD in the non-volatile storage and the proper method for accessing the non-volatile storage.The segment selector in one operating mode is therefore different from the segment selector for another operating mode.Further, the need for a segment selector from an operating system to update ESCD has required a different selector if an ESCD area is relocated.ESCD generally allows Plug and Play System Basic Input Output Services (BIOS) code to more fully configure a computer system at power up by specifying the system resources assigned to devices that have been installed in the system.The portion of non-volatile storage used to store the ESCD may be only a subset of the total non-volatile storage available in a computer system.Option ROM represents a designated area of ROM space which an operating system preferably is programmed not to utilize.

During Power-On-Self-Test (POST) code, a ROM image is copied from an ESCD sector of a read-only memory to an ESCD original buffer and an ESCD write buffer....

ESCD information may be used by POST to allocate system resources to all configurable devices that are known to the system BIOS.

System resources typically include Direct Memory Access (DMA) channels, Interrupt Request Lines (IRQ's), Input/Output (I/O) addresses, and memory.

During Power-On-Self-Test (POST) code, a ROM image is copied from an ESCD sector of a read-only memory to an ESCD original buffer and an ESCD write buffer. Following the POST operations, the contents of the ESCD write buffer are copied to an ESCD runtime buffer.

The contents of the ESCD original buffer or the ESCD sector are compared to the contents of the ESCD runtime buffer.

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