From Beyond BIOS: Implementing the Unified Extensible Firmware Interface with Intel's Framework
I just invent, then wait until man comes around to needing what I invented.
R. Buckminster Fuller
Overview
EFI has over time evolved a very basic paradigm for establishing a firmware policy engine. The concept was developed prior to the inception of the framework (EFI 1.1 or earlier) of a single boot manager whose sole purpose was exercising the policy established by some architecturally defined global NVRAM variables. As the framework evolved, and several distinct boot phases such as SEC, PEI, DXE, BDS, Runtime, and Afterlife were defined, the BDS (Boot Device Selection) phase became a distinct Boot Manager-like phase. In this chapter, the architectural components that steer the policy of the Boot Manager are reviewed. This content forms the architectural basis for what eventually became the BDS phase. Selection
In fact, the differences between what is known as the boot manager in pre-Framework solutions and what is known as the BDS in Framework solutions is easy to illustrate. Figure 13.1 shows the software flow in an EFI 1.1 compatible (pre-Framework) environment, and Figure 13.2 shows one that is Framework compatible.
Figure 13.1: EFI with Boot Manager Component
Figure 13.2: Framework with BDS Component
As you can see from comparing the two figures, there is much overlap. The BDS phase subsumes the direction described in this chapter and is further explained in Chapter 9.
The EFI boot manager is a firmware policy engine that can be configured by modifying architecturally defined global NVRAM variables. The boot manager attempts to...
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Topics of Interest
Two roads diverged in a wood . Robert Frost, "The Road Less Taken" Overview The restart of a system admits to many possibilities, or paths of execution. The restart of a CPU execution for a...
Functional Visualization of CSM After all necessary DXE drivers are executed and the DXE Foundation produces the EFI Boot Services and EFI Runtime Services, the DXE Dispatcher transfers the control...
I do not fear computers. I fear the lack of them. Isaac Asimov Overview This chapter describes the makeup of the Driver Execution Environment (DXE) and how it operates during the platform...
Small is Beautiful E.F. Schumacher The pre-EFI initialization (PEI) phase of execution has two primary roles in a platforms life: determine the source of the restart and provide a minimum amount...
Adding manpower to a late software project makes it later. Brook's Law Overview This chapter describes the fundamental services that are made available in an EFI-compliant system. The services...
