HOB List

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The HOB list contains all the information that the DXE Foundation requires to produce its memory-based services. The HOB list contains information on the boot mode, the processor’s instruction set, and the memory that was discovered in the PEI phase. It also contains a description of the system memory that was initialized by the PEI phase, along with information about the firmware devices that were discovered in the PEI phase. The firmware device information includes the system memory locations of the firmware devices and of the firmware volumes that are contained within those firmware devices. The firmware volumes may contain DXE drivers, and the DXE Dispatcher is responsible for loading and executing the DXE drivers that are discovered in those firmware volumes. Finally, the HOB list may contain the I/O resources and memory-mapped I/O resources that were discovered in the PEI phase.

A HOB list is always terminated by an end-of-list HOB. The one additional HOB type that is not shown in the figure is the GUID extension HOB that allows a PEIM to pass private data to a DXE driver. Only the DXE driver that recognizes the GUID value in the GUID extension HOB will be able to understand the data in that HOB. The HOB entries are all designed to be position independent. This independence allows the DXE Foundation to relocate the HOB list to a different location if it is not suitable to the DXE Foundation.

Copyright (C) 2008,2010 Phoenix Technologies Ltd. All Rights Reserved. Portions copyright © 2004 Intel Corporation. Used with permission.

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