UEFI Protocols

Overview

UEFI protocols are the main mechanism used by firmware to expose functionality to applications and boot loaders.

Instead of directly accessing hardware, UEFI applications locate protocols that provide standardized interfaces.

Examples include:

Filesystem access
Graphics output
Device communication
Loaded image information

Protocol Concept

A protocol is a structure containing function pointers and related data.

An application does not need to know the hardware implementation behind a protocol.

The simplified workflow is:

EFI Application
      |
      v
LocateProtocol()
      |
      v
UEFI Protocol Interface
      |
      v
Firmware Implementation

This allows the same application to run on different firmware implementations.

Locating a Protocol

Protocols are usually discovered through Boot Services:

LocateProtocol()
        |
        v
Protocol GUID
        |
        v
Protocol Interface

The application provides a protocol identifier (GUID), and firmware returns a pointer to the corresponding interface.

Protocols Used in This Project

Simple File System Protocol

The Filesystem Explorer uses:

EFI_SIMPLE_FILE_SYSTEM_PROTOCOL

It provides access to EFI volumes and allows applications to:

Open filesystem volumes
Access the root directory
Read and write files

Workflow:

    LocateProtocol()
            |
            v
    EFI_SIMPLE_FILE_SYSTEM_PROTOCOL
            |
            v
    OpenVolume()
            |
            v
    EFI_FILE_PROTOCOL

Graphics Output Protocol

The Graphics Demo uses:

EFI_GRAPHICS_OUTPUT_PROTOCOL

It provides access to framebuffer-based graphics.

The application can:

Query available modes
Change graphics modes
Access framebuffer memory
Render pixels directly

Why Protocols Matter

Protocols separate application logic from firmware implementation.

An application does not need to know:

Which graphics hardware is installed
Which filesystem implementation is used
How the firmware communicates with devices

It only needs to use the defined protocol interface.

Project Usage

Understanding protocols is essential for UEFI development.

The applications in this project use protocols to access functionality provided by the firmware before an operating system is running.