Overview

This chapter describes how EFI extends the traditional boundaries of console support in the pre-boot phase and provides a series of software layering approaches that are commonly used in EFI-compliant platforms. Most platforms, at minimum, would have a text-based console for a user to either locally or remotely interact with the system. A variety of mechanisms can accomplish this communication in EFI. Whether it is through a remote interface, through a local keyboard and monitor, or even a remote network connection, each has a common root that can be thought of as the basic EFI console support. This support is used to handle input and output of text-based information intended for the system user during the operation of code in the EFI boot services environment. These console definitions are split into three types of console devices: one for input, and one each for normal output and errors.

These interfaces are specified by function call definitions to allow maximum flexibility in implementation. For example, a compliant system is not required to have a keyboard or screen directly connected to the system. As long as the semantics of the functions are preserved, implementations may direct information using these interfaces in any way that succeeds in passing the information to the system user

The EFI console is built out of two primary protocols, and these are EFI Simple Text Input and EFI Simple Text Output...