LegacyRegion2

Overview

Manages PAM (Programmable Attribute Map) registers to control read/write/execute permissions on the legacy VGA/BIOS memory region (0xC0000--0xFFFFF). Installs the EFI_LEGACY_REGION2_PROTOCOL, which allows other DXE drivers to decode, lock, and unlock the 13 legacy PAM segments covering the VGA BIOS, option ROM, and system BIOS shadow regions. This driver is essential for legacy OS compatibility and SMM-based memory protection during boot.

Key Functions

• ModuleEntryPoint -- Entry point; initializes globals and calls driver main routine
• LegacyRegion2Decode -- Enables or disables legacy region decoding for a specified address range
• LegacyRegion2Lock -- Locks the PAM register configuration to prevent modification
• LegacyRegion2BootOrg -- Programs chipset registers to restore PAM defaults for legacy boot
• GetPamRegister -- Returns the chipset PAM register index corresponding to a legacy memory address

Dependencies

• EFI_LEGACY_REGION2_PROTOCOL (installed by this driver)
• EFI_LEGACY_REGION_PROTOCOL (compatibility)
• UEFI Boot/Runtime Services

Platform

Intel x86-64 (PE32+), Purley platform (HR650X). UEFI subsystem.