path: root/IntelFrameworkModulePkg/Csm/LegacyBiosDxe/LegacyBiosInterface.h

/** @file

Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>

This program and the accompanying materials
are licensed and made available under the terms and conditions
of the BSD License which accompanies this distribution.  The
full text of the license may be found at
http://opensource.org/licenses/bsd-license.php

THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.

**/

#ifndef _LEGACY_BIOS_INTERFACE_
#define _LEGACY_BIOS_INTERFACE_


#include <FrameworkDxe.h>
#include <IndustryStandard/Pci.h>
#include <IndustryStandard/SmBios.h>
#include <IndustryStandard/Acpi10.h>

#include <Guid/SmBios.h>
#include <Guid/Acpi.h>
#include <Guid/DxeServices.h>
#include <Guid/LegacyBios.h>
#include <Guid/StatusCodeDataTypeId.h>
#include <Guid/ImageAuthentication.h>

#include <Protocol/BlockIo.h>
#include <Protocol/LoadedImage.h>
#include <Protocol/PciIo.h>
#include <Protocol/Cpu.h>
#include <Protocol/Timer.h>
#include <Protocol/IsaIo.h>
#include <Protocol/LegacyRegion2.h>
#include <Protocol/SimpleTextIn.h>
#include <Protocol/LegacyInterrupt.h>
#include <Protocol/LegacyBios.h>
#include <Protocol/DiskInfo.h>
#include <Protocol/GenericMemoryTest.h>
#include <Protocol/LegacyBiosPlatform.h>
#include <Protocol/DevicePath.h>
#include <Protocol/Legacy8259.h>
#include <Protocol/PciRootBridgeIo.h>
#include <Protocol/SerialIo.h>
#include <Protocol/SuperIo.h>

#include <Library/BaseLib.h>
#include <Library/DebugLib.h>
#include <Library/UefiLib.h>
#include <Library/BaseMemoryLib.h>
#include <Library/ReportStatusCodeLib.h>
#include <Library/UefiRuntimeServicesTableLib.h>
#include <Library/HobLib.h>
#include <Library/UefiDriverEntryPoint.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/IoLib.h>
#include <Library/PcdLib.h>
#include <Library/DevicePathLib.h>
#include <Library/DxeServicesTableLib.h>
#include <Library/PeCoffLib.h>
#include <Library/CacheMaintenanceLib.h>
#include <Library/DebugAgentLib.h>

//
// BUGBUG: This entry maybe changed to PCD in future and wait for
//         redesign of BDS library
//
#define MAX_BBS_ENTRIES 0x100

//
// Thunk Status Codes
//   (These apply only to errors with the thunk and not to the code that was
//   thunked to.)
//
#define THUNK_OK              0x00
#define THUNK_ERR_A20_UNSUP   0x01
#define THUNK_ERR_A20_FAILED  0x02

//
// Vector base definitions
//
//
// 8259 Hardware definitions
//
#define LEGACY_MODE_BASE_VECTOR_MASTER     0x08
#define LEGACY_MODE_BASE_VECTOR_SLAVE      0x70

//
// The original PC used INT8-F for master PIC. Since these mapped over
// processor exceptions TIANO moved the master PIC to INT68-6F.
//
// The vector base for slave PIC is set as 0x70 for PC-AT compatibility.
//
#define PROTECTED_MODE_BASE_VECTOR_MASTER  0x68
#define PROTECTED_MODE_BASE_VECTOR_SLAVE   0x70

//
// When we call CSM16 functions, some CSM16 use es:[offset + 0xabcd] to get data passed from CSM32, 
// offset + 0xabcd could overflow which exceeds 0xFFFF which is invalid in real mode. 
// So this will keep offset as small as possible to avoid offset overflow in real mode. 
//
#define NORMALIZE_EFI_SEGMENT(_Adr)      (UINT16) (((UINTN) (_Adr)) >> 4)
#define NORMALIZE_EFI_OFFSET(_Adr)       (UINT16) (((UINT16) ((UINTN) (_Adr))) & 0xf)

//
// Trace defines
//
//
#define LEGACY_BDA_TRACE    0x000
#define LEGACY_BIOS_TRACE   0x040
#define LEGACY_BOOT_TRACE   0x080
#define LEGACY_CMOS_TRACE   0x0C0
#define LEGACY_IDE_TRACE    0x100
#define LEGACY_MP_TRACE     0x140
#define LEGACY_PCI_TRACE    0x180
#define LEGACY_SIO_TRACE    0x1C0

#define LEGACY_PCI_TRACE_000 LEGACY_PCI_TRACE + 0x00
#define LEGACY_PCI_TRACE_001 LEGACY_PCI_TRACE + 0x01
#define LEGACY_PCI_TRACE_002 LEGACY_PCI_TRACE + 0x02
#define LEGACY_PCI_TRACE_003 LEGACY_PCI_TRACE + 0x03
#define LEGACY_PCI_TRACE_004 LEGACY_PCI_TRACE + 0x04
#define LEGACY_PCI_TRACE_005 LEGACY_PCI_TRACE + 0x05
#define LEGACY_PCI_TRACE_006 LEGACY_PCI_TRACE + 0x06
#define LEGACY_PCI_TRACE_007 LEGACY_PCI_TRACE + 0x07
#define LEGACY_PCI_TRACE_008 LEGACY_PCI_TRACE + 0x08
#define LEGACY_PCI_TRACE_009 LEGACY_PCI_TRACE + 0x09
#define LEGACY_PCI_TRACE_00A LEGACY_PCI_TRACE + 0x0A
#define LEGACY_PCI_TRACE_00B LEGACY_PCI_TRACE + 0x0B
#define LEGACY_PCI_TRACE_00C LEGACY_PCI_TRACE + 0x0C
#define LEGACY_PCI_TRACE_00D LEGACY_PCI_TRACE + 0x0D
#define LEGACY_PCI_TRACE_00E LEGACY_PCI_TRACE + 0x0E
#define LEGACY_PCI_TRACE_00F LEGACY_PCI_TRACE + 0x0F

#define BDA_VIDEO_MODE      0x49

#define IDE_PI_REGISTER_PNE     BIT0
#define IDE_PI_REGISTER_SNE     BIT2

typedef struct {
  UINTN   PciSegment;
  UINTN   PciBus;
  UINTN   PciDevice;
  UINTN   PciFunction;
  UINT32  ShadowAddress;
  UINT32  ShadowedSize;
  UINT8   DiskStart;
  UINT8   DiskEnd;
} ROM_INSTANCE_ENTRY;

//
// Values for RealModeGdt
//
#if defined (MDE_CPU_IA32)

#define NUM_REAL_GDT_ENTRIES  3
#define CONVENTIONAL_MEMORY_TOP 0xA0000   // 640 KB
#define INITIAL_VALUE_BELOW_1K  0x0

#elif defined (MDE_CPU_X64)

#define NUM_REAL_GDT_ENTRIES  8
#define CONVENTIONAL_MEMORY_TOP 0xA0000   // 640 KB
#define INITIAL_VALUE_BELOW_1K  0x0

#elif defined (MDE_CPU_IPF)

#define NUM_REAL_GDT_ENTRIES  3
#define CONVENTIONAL_MEMORY_TOP 0x80000   // 512 KB
#define INITIAL_VALUE_BELOW_1K  0xff

#endif

#pragma pack(1)

//
// Define what a processor GDT looks like
//
typedef struct {
  UINT32  LimitLo : 16;
  UINT32  BaseLo : 16;
  UINT32  BaseMid : 8;
  UINT32  Type : 4;
  UINT32  System : 1;
  UINT32  Dpl : 2;
  UINT32  Present : 1;
  UINT32  LimitHi : 4;
  UINT32  Software : 1;
  UINT32  Reserved : 1;
  UINT32  DefaultSize : 1;
  UINT32  Granularity : 1;
  UINT32  BaseHi : 8;
} GDT32;

typedef struct {
  UINT16  LimitLow;
  UINT16  BaseLow;
  UINT8   BaseMid;
  UINT8   Attribute;
  UINT8   LimitHi;
  UINT8   BaseHi;
} GDT64;

//
// Define what a processor descriptor looks like
// This data structure must be kept in sync with ASM STRUCT in Thunk.inc
//
typedef struct {
  UINT16  Limit;
  UINT64  Base;
} DESCRIPTOR64;

typedef struct {
  UINT16  Limit;
  UINT32  Base;
} DESCRIPTOR32;

//
// Low stub lay out
//
#define LOW_STACK_SIZE      (8 * 1024)  // 8k?
#define EFI_MAX_E820_ENTRY  100
#define FIRST_INSTANCE      1
#define NOT_FIRST_INSTANCE  0

#if defined (MDE_CPU_IA32)
typedef struct {
  //
  // Space for the code
  //  The address of Code is also the beginning of the relocated Thunk code
  //
  CHAR8                             Code[4096]; // ?
  //
  // The address of the Reverse Thunk code
  //  Note that this member CONTAINS the address of the relocated reverse thunk
  //  code unlike the member variable 'Code', which IS the address of the Thunk
  //  code.
  //
  UINT32                            LowReverseThunkStart;

  //
  // Data for the code (cs releative)
  //
  DESCRIPTOR32                      GdtDesc;          // Protected mode GDT
  DESCRIPTOR32                      IdtDesc;          // Protected mode IDT
  UINT32                            FlatSs;
  UINT32                            FlatEsp;

  UINT32                            LowCodeSelector;  // Low code selector in GDT
  UINT32                            LowDataSelector;  // Low data selector in GDT
  UINT32                            LowStack;
  DESCRIPTOR32                      RealModeIdtDesc;

  //
  // real-mode GDT (temporary GDT with two real mode segment descriptors)
  //
  GDT32                             RealModeGdt[NUM_REAL_GDT_ENTRIES];
  DESCRIPTOR32                      RealModeGdtDesc;

  //
  // Members specifically for the reverse thunk
  //  The RevReal* members are used to store the current state of real mode
  //  before performing the reverse thunk.  The RevFlat* members must be set
  //  before calling the reverse thunk assembly code.
  //
  UINT16                            RevRealDs;
  UINT16                            RevRealSs;
  UINT32                            RevRealEsp;
  DESCRIPTOR32                      RevRealIdtDesc;
  UINT16                            RevFlatDataSelector;  // Flat data selector in GDT
  UINT32                            RevFlatStack;

  //
  // A low memory stack
  //
  CHAR8                             Stack[LOW_STACK_SIZE];

  //
  // Stack for flat mode after reverse thunk
  // @bug    - This may no longer be necessary if the reverse thunk interface
  //           is changed to have the flat stack in a different location.
  //
  CHAR8                             RevThunkStack[LOW_STACK_SIZE];

  //
  // Legacy16 Init memory map info
  //
  EFI_TO_COMPATIBILITY16_INIT_TABLE EfiToLegacy16InitTable;

  EFI_TO_COMPATIBILITY16_BOOT_TABLE EfiToLegacy16BootTable;

  CHAR8                             InterruptRedirectionCode[32];
  EFI_LEGACY_INSTALL_PCI_HANDLER    PciHandler;
  EFI_DISPATCH_OPROM_TABLE          DispatchOpromTable;
  BBS_TABLE                         BbsTable[MAX_BBS_ENTRIES];
} LOW_MEMORY_THUNK;

#elif defined (MDE_CPU_X64)

typedef struct {
  //
  // Space for the code
  //  The address of Code is also the beginning of the relocated Thunk code
  //
  CHAR8                             Code[4096]; // ?

  //
  // Data for the code (cs releative)
  //
  DESCRIPTOR64                      X64GdtDesc;          // Protected mode GDT
  DESCRIPTOR64                      X64IdtDesc;          // Protected mode IDT
  UINTN                             X64Ss;
  UINTN                             X64Esp;

  UINTN                             RealStack;
  DESCRIPTOR32                      RealModeIdtDesc;
  DESCRIPTOR32                      RealModeGdtDesc;

  //
  // real-mode GDT (temporary GDT with two real mode segment descriptors)
  //
  GDT64                             RealModeGdt[NUM_REAL_GDT_ENTRIES];
  UINT64                            PageMapLevel4;

  //
  // A low memory stack
  //
  CHAR8                             Stack[LOW_STACK_SIZE];

  //
  // Legacy16 Init memory map info
  //
  EFI_TO_COMPATIBILITY16_INIT_TABLE EfiToLegacy16InitTable;

  EFI_TO_COMPATIBILITY16_BOOT_TABLE EfiToLegacy16BootTable;

  CHAR8                             InterruptRedirectionCode[32];
  EFI_LEGACY_INSTALL_PCI_HANDLER    PciHandler;
  EFI_DISPATCH_OPROM_TABLE          DispatchOpromTable;
  BBS_TABLE                         BbsTable[MAX_BBS_ENTRIES];
} LOW_MEMORY_THUNK;

#elif defined (MDE_CPU_IPF)

typedef struct {
  //
  // Space for the code
  //  The address of Code is also the beginning of the relocated Thunk code
  //
  CHAR8                             Code[4096]; // ?
  //
  // The address of the Reverse Thunk code
  //  Note that this member CONTAINS the address of the relocated reverse thunk
  //  code unlike the member variable 'Code', which IS the address of the Thunk
  //  code.
  //
  UINT32                            LowReverseThunkStart;

  //
  // Data for the code (cs releative)
  //
  DESCRIPTOR32                      GdtDesc;          // Protected mode GDT
  DESCRIPTOR32                      IdtDesc;          // Protected mode IDT
  UINT32                            FlatSs;
  UINT32                            FlatEsp;

  UINT32                            LowCodeSelector;  // Low code selector in GDT
  UINT32                            LowDataSelector;  // Low data selector in GDT
  UINT32                            LowStack;
  DESCRIPTOR32                      RealModeIdtDesc;

  //
  // real-mode GDT (temporary GDT with two real mode segment descriptors)
  //
  GDT32                             RealModeGdt[NUM_REAL_GDT_ENTRIES];
  DESCRIPTOR32                      RealModeGdtDesc;

  //
  // Members specifically for the reverse thunk
  //  The RevReal* members are used to store the current state of real mode
  //  before performing the reverse thunk.  The RevFlat* members must be set
  //  before calling the reverse thunk assembly code.
  //
  UINT16                            RevRealDs;
  UINT16                            RevRealSs;
  UINT32                            RevRealEsp;
  DESCRIPTOR32                      RevRealIdtDesc;
  UINT16                            RevFlatDataSelector;  // Flat data selector in GDT
  UINT32                            RevFlatStack;

  //
  // A low memory stack
  //
  CHAR8                             Stack[LOW_STACK_SIZE];

  //
  // Stack for flat mode after reverse thunk
  // @bug - This may no longer be necessary if the reverse thunk interface
  //           is changed to have the flat stack in a different location.
  //
  CHAR8                             RevThunkStack[LOW_STACK_SIZE];

  //
  // Legacy16 Init memory map info
  //
  EFI_TO_COMPATIBILITY16_INIT_TABLE EfiToLegacy16InitTable;

  EFI_TO_COMPATIBILITY16_BOOT_TABLE EfiToLegacy16BootTable;

  CHAR8                             InterruptRedirectionCode[32];
  EFI_LEGACY_INSTALL_PCI_HANDLER    PciHandler;
  EFI_DISPATCH_OPROM_TABLE          DispatchOpromTable;
  BBS_TABLE                         BbsTable[MAX_BBS_ENTRIES];
} LOW_MEMORY_THUNK;

#endif

//
// PnP Expansion Header
//
typedef struct {
  UINT32  PnpSignature;
  UINT8   Revision;
  UINT8   Length;
  UINT16  NextHeader;
  UINT8   Reserved1;
  UINT8   Checksum;
  UINT32  DeviceId;
  UINT16  MfgPointer;
  UINT16  ProductNamePointer;
  UINT8   Class;
  UINT8   SubClass;
  UINT8   Interface;
  UINT8   DeviceIndicators;
  UINT16  Bcv;
  UINT16  DisconnectVector;
  UINT16  Bev;
  UINT16  Reserved2;
  UINT16  StaticResourceVector;
} LEGACY_PNP_EXPANSION_HEADER;

typedef struct {
  UINT8   PciSegment;
  UINT8   PciBus;
  UINT8   PciDevice;
  UINT8   PciFunction;
  UINT16  Vid;
  UINT16  Did;
  UINT16  SysSid;
  UINT16  SVid;
  UINT8   Class;
  UINT8   SubClass;
  UINT8   Interface;
  UINT8   Reserved;
  UINTN   RomStart;
  UINTN   ManufacturerString;
  UINTN   ProductNameString;
} LEGACY_ROM_AND_BBS_TABLE;

//
// Structure how EFI has mapped a devices HDD drive numbers.
// Boot to EFI aware OS or shell requires this mapping when
// 16-bit CSM assigns drive numbers.
// This mapping is ignored booting to a legacy OS.
//
typedef struct {
  UINT8 PciSegment;
  UINT8 PciBus;
  UINT8 PciDevice;
  UINT8 PciFunction;
  UINT8 StartDriveNumber;
  UINT8 EndDriveNumber;
} LEGACY_EFI_HDD_TABLE;

//
// This data is passed to Leacy16Boot
//
typedef enum {
  EfiAcpiAddressRangeMemory   = 1,
  EfiAcpiAddressRangeReserved = 2,
  EfiAcpiAddressRangeACPI     = 3,
  EfiAcpiAddressRangeNVS      = 4,
  EfiAddressRangePersistentMemory = 7
} EFI_ACPI_MEMORY_TYPE;

typedef struct {
  UINT64                BaseAddr;
  UINT64                Length;
  EFI_ACPI_MEMORY_TYPE  Type;
} EFI_E820_ENTRY64;

typedef struct {
  UINT32                BassAddrLow;
  UINT32                BaseAddrHigh;
  UINT32                LengthLow;
  UINT32                LengthHigh;
  EFI_ACPI_MEMORY_TYPE  Type;
} EFI_E820_ENTRY;

#pragma pack()

extern BBS_TABLE           *mBbsTable;

extern EFI_GENERIC_MEMORY_TEST_PROTOCOL *gGenMemoryTest;

#define PORT_70 0x70
#define PORT_71 0x71

#define CMOS_0A     0x0a  ///< Status register A
#define CMOS_0D     0x0d  ///< Status register D
#define CMOS_0E     0x0e  ///< Diagnostic Status
#define CMOS_0F     0x0f  ///< Shutdown status
#define CMOS_10     0x10  ///< Floppy type
#define CMOS_12     0x12  ///< IDE type
#define CMOS_14     0x14  ///< Same as BDA 40:10
#define CMOS_15     0x15  ///< Low byte of base memory in 1k increments
#define CMOS_16     0x16  ///< High byte of base memory in 1k increments
#define CMOS_17     0x17  ///< Low byte of 1MB+ memory in 1k increments - max 15 MB
#define CMOS_18     0x18  ///< High byte of 1MB+ memory in 1k increments - max 15 MB
#define CMOS_19     0x19  ///< C: extended drive type
#define CMOS_1A     0x1a  ///< D: extended drive type
#define CMOS_2E     0x2e  ///< Most significient byte of standard checksum
#define CMOS_2F     0x2f  ///< Least significient byte of standard checksum
#define CMOS_30     0x30  ///< CMOS 0x17
#define CMOS_31     0x31  ///< CMOS 0x18
#define CMOS_32     0x32  ///< Century byte

//
// 8254 Timer registers
//
#define TIMER0_COUNT_PORT                         0x40
#define TIMER1_COUNT_PORT                         0x41
#define TIMER2_COUNT_PORT                         0x42
#define TIMER_CONTROL_PORT                        0x43

//
// Timer 0, Read/Write LSB then MSB, Square wave output, binary count use.
//
#define TIMER0_CONTROL_WORD         0x36      

#define LEGACY_BIOS_INSTANCE_SIGNATURE  SIGNATURE_32 ('L', 'B', 'I', 'T')
typedef struct {
  UINTN                             Signature;

  EFI_HANDLE                        Handle;
  EFI_LEGACY_BIOS_PROTOCOL          LegacyBios;

  EFI_HANDLE                        ImageHandle;

  //
  // CPU Architectural Protocol 
  //
  EFI_CPU_ARCH_PROTOCOL             *Cpu;

  //
  // Timer Architectural Protocol 
  //
  EFI_TIMER_ARCH_PROTOCOL           *Timer;
  BOOLEAN                           TimerUses8254; 
  
  //
  // Protocol to Lock and Unlock 0xc0000 - 0xfffff
  //
  EFI_LEGACY_REGION2_PROTOCOL       *LegacyRegion;

  EFI_LEGACY_BIOS_PLATFORM_PROTOCOL *LegacyBiosPlatform;

  //
  // Interrupt control for thunk and PCI IRQ
  //
  EFI_LEGACY_8259_PROTOCOL          *Legacy8259;
  
  //
  // PCI Interrupt PIRQ control
  //
  EFI_LEGACY_INTERRUPT_PROTOCOL     *LegacyInterrupt;

  //
  // Generic Memory Test
  //
  EFI_GENERIC_MEMORY_TEST_PROTOCOL  *GenericMemoryTest;

  //
  // TRUE if PCI Interupt Line registers have been programmed.
  //
  BOOLEAN                           PciInterruptLine;

  //
  // Code space below 1MB needed by thunker to transition to real mode.
  // Contains stack and real mode code fragments
  //
  LOW_MEMORY_THUNK                  *IntThunk;

  //
  // Starting shadow address of the Legacy BIOS
  //
  UINT32                            BiosStart;
  UINT32                            LegacyBiosImageSize;

  //
  // Start of variables used by CsmItp.mac ITP macro file and/os LegacyBios
  //
  UINT8                             Dump[4];

  //
  // $EFI Legacy16 code entry info in memory < 1 MB;
  //
  EFI_COMPATIBILITY16_TABLE         *Legacy16Table;
  VOID                              *Legacy16InitPtr;
  VOID                              *Legacy16BootPtr;
  VOID                              *InternalIrqRoutingTable;
  UINT32                            NumberIrqRoutingEntries;
  VOID                              *BbsTablePtr;
  VOID                              *HddTablePtr;
  UINT32                            NumberHddControllers;

  //
  // Cached copy of Legacy16 entry point
  //
  UINT16                            Legacy16CallSegment;
  UINT16                            Legacy16CallOffset;

  //
  // Returned from $EFI and passed in to OPROMS
  //
  UINT16                            PnPInstallationCheckSegment;
  UINT16                            PnPInstallationCheckOffset;

  //
  // E820 table
  //
  EFI_E820_ENTRY                    E820Table[EFI_MAX_E820_ENTRY];
  UINT32                            NumberE820Entries;

  //
  // True if legacy VGA INT 10h handler installed
  //
  BOOLEAN                           VgaInstalled;

  //
  // Number of IDE drives
  //
  UINT8                             IdeDriveCount;

  //
  // Current Free Option ROM space. An option ROM must NOT go past
  // BiosStart.
  //
  UINT32                            OptionRom;

  //
  // Save Legacy16 unexpected interrupt vector. Reprogram INT 68-6F from
  // EFI values to legacy value just before boot.
  //
  UINT32                            BiosUnexpectedInt;
  UINT32                            ThunkSavedInt[8];
  UINT16                            ThunkSeg;
  LEGACY_EFI_HDD_TABLE              *LegacyEfiHddTable;
  UINT16                            LegacyEfiHddTableIndex;
  UINT8                             DiskEnd;
  UINT8                             Disk4075;
  UINT16                            TraceIndex;
  UINT16                            Trace[0x200];

  //
  // Indicate that whether GenericLegacyBoot is entered or not
  //
  BOOLEAN                           LegacyBootEntered;                              

  //
  // CSM16 PCI Interface Version
  //
  UINT16                            Csm16PciInterfaceVersion;

} LEGACY_BIOS_INSTANCE;


#pragma pack(1)

/*
  40:00-01 Com1
  40:02-03 Com2
  40:04-05 Com3
  40:06-07 Com4
  40:08-09 Lpt1
  40:0A-0B Lpt2
  40:0C-0D Lpt3
  40:0E-0E Ebda segment
  40:10-11 MachineConfig
  40:12    Bda12 - skip
  40:13-14 MemSize below 1MB
  40:15-16 Bda15_16 - skip
  40:17    Keyboard Shift status
  40:18-19 Bda18_19 - skip
  40:1A-1B Key buffer head
  40:1C-1D Key buffer tail
  40:1E-3D Bda1E_3D- key buffer -skip
  40:3E-3F FloppyData 3E = Calibration status 3F = Motor status
  40:40    FloppyTimeout
  40:41-74 Bda41_74 - skip
  40:75    Number of HDD drives
  40:76-77 Bda76_77 - skip
  40:78-79 78 = Lpt1 timeout, 79 = Lpt2 timeout
  40:7A-7B 7A = Lpt3 timeout, 7B = Lpt4 timeout
  40:7C-7D 7C = Com1 timeout, 7D = Com2 timeout
  40:7E-7F 7E = Com3 timeout, 7F = Com4 timeout
  40:80-81 Pointer to start of key buffer
  40:82-83 Pointer to end of key buffer
  40:84-87 Bda84_87 - skip
  40:88    HDD Data Xmit rate
  40:89-8f skip
  40:90    Floppy data rate
  40:91-95 skip
  40:96    Keyboard Status
  40:97    LED Status
  40:98-101 skip
*/
typedef struct {
  UINT16  Com1;
  UINT16  Com2;
  UINT16  Com3;
  UINT16  Com4;
  UINT16  Lpt1;
  UINT16  Lpt2;
  UINT16  Lpt3;
  UINT16  Ebda;
  UINT16  MachineConfig;
  UINT8   Bda12;
  UINT16  MemSize;
  UINT8   Bda15_16[0x02];
  UINT8   ShiftStatus;
  UINT8   Bda18_19[0x02];
  UINT16  KeyHead;
  UINT16  KeyTail;
  UINT16  Bda1E_3D[0x10];
  UINT16  FloppyData;
  UINT8   FloppyTimeout;
  UINT8   Bda41_74[0x34];
  UINT8   NumberOfDrives;
  UINT8   Bda76_77[0x02];
  UINT16  Lpt1_2Timeout;
  UINT16  Lpt3_4Timeout;
  UINT16  Com1_2Timeout;
  UINT16  Com3_4Timeout;
  UINT16  KeyStart;
  UINT16  KeyEnd;
  UINT8   Bda84_87[0x4];
  UINT8   DataXmit;
  UINT8   Bda89_8F[0x07];
  UINT8   FloppyXRate;
  UINT8   Bda91_95[0x05];
  UINT8   KeyboardStatus;
  UINT8   LedStatus;
} BDA_STRUC;
#pragma pack()

#define LEGACY_BIOS_INSTANCE_FROM_THIS(this)  CR (this, LEGACY_BIOS_INSTANCE, LegacyBios, LEGACY_BIOS_INSTANCE_SIGNATURE)

/**
  Thunk to 16-bit real mode and execute a software interrupt with a vector
  of BiosInt. Regs will contain the 16-bit register context on entry and
  exit.

  @param  This    Protocol instance pointer.
  @param  BiosInt Processor interrupt vector to invoke
  @param  Regs    Register contexted passed into (and returned) from thunk to
                  16-bit mode

  @retval FALSE   Thunk completed, and there were no BIOS errors in the target code.
                  See Regs for status.
  @retval TRUE     There was a BIOS erro in the target code.

**/
BOOLEAN
EFIAPI
LegacyBiosInt86 (
  IN  EFI_LEGACY_BIOS_PROTOCOL          *This,
  IN  UINT8                             BiosInt,
  IN  EFI_IA32_REGISTER_SET             *Regs
  );


/**
  Thunk to 16-bit real mode and call Segment:Offset. Regs will contain the
  16-bit register context on entry and exit. Arguments can be passed on
  the Stack argument

  @param  This                   Protocol instance pointer.
  @param  Segment                Segemnt of 16-bit mode call
  @param  Offset                 Offset of 16-bit mdoe call
  @param  Regs                   Register contexted passed into (and returned) from
                                 thunk to  16-bit mode
  @param  Stack                  Caller allocated stack used to pass arguments
  @param  StackSize              Size of Stack in bytes

  @retval FALSE                  Thunk completed, and there were no BIOS errors in
                                 the target code. See Regs for status.
  @retval TRUE                   There was a BIOS erro in the target code.

**/
BOOLEAN
EFIAPI
LegacyBiosFarCall86 (
  IN  EFI_LEGACY_BIOS_PROTOCOL          *This,
  IN  UINT16                            Segment,
  IN  UINT16                            Offset,
  IN  EFI_IA32_REGISTER_SET             *Regs,
  IN  VOID                              *Stack,
  IN  UINTN                             StackSize
  );


/**
  Test to see if a legacy PCI ROM exists for this device. Optionally return
  the Legacy ROM instance for this PCI device.

  @param  This                   Protocol instance pointer.
  @param  PciHandle              The PCI PC-AT OPROM from this devices ROM BAR will
                                 be loaded
  @param  RomImage               Return the legacy PCI ROM for this device
  @param  RomSize                Size of ROM Image
  @param  Flags                  Indicates if ROM found and if PC-AT.

  @retval EFI_SUCCESS            Legacy Option ROM availible for this device
  @retval EFI_UNSUPPORTED        Legacy Option ROM not supported.

**/
EFI_STATUS
EFIAPI
LegacyBiosCheckPciRom (
  IN  EFI_LEGACY_BIOS_PROTOCOL          *This,
  IN  EFI_HANDLE                        PciHandle,
  OUT VOID                              **RomImage, OPTIONAL
  OUT UINTN                             *RomSize, OPTIONAL
  OUT UINTN                             *Flags
  );


/**
  Assign drive number to legacy HDD drives prior to booting an EFI
  aware OS so the OS can access drives without an EFI driver.
  Note: BBS compliant drives ARE NOT available until this call by
  either shell or EFI.

  @param  This                   Protocol instance pointer.
  @param  BbsCount               Number of BBS_TABLE structures
  @param  BbsTable               List BBS entries

  @retval EFI_SUCCESS            Drive numbers assigned

**/
EFI_STATUS
EFIAPI
LegacyBiosPrepareToBootEfi (
  IN EFI_LEGACY_BIOS_PROTOCOL         *This,
  OUT UINT16                          *BbsCount,
  OUT BBS_TABLE                       **BbsTable
  );


/**
  To boot from an unconventional device like parties and/or execute
  HDD diagnostics.

  @param  This                   Protocol instance pointer.
  @param  Attributes             How to interpret the other input parameters
  @param  BbsEntry               The 0-based index into the BbsTable for the parent
                                  device.
  @param  BeerData               Pointer to the 128 bytes of ram BEER data.
  @param  ServiceAreaData        Pointer to the 64 bytes of raw Service Area data.
                                 The caller must provide a pointer to the specific
                                 Service Area and not the start all Service Areas.
 EFI_INVALID_PARAMETER if error. Does NOT return if no error.

**/
EFI_STATUS
EFIAPI
LegacyBiosBootUnconventionalDevice (
  IN EFI_LEGACY_BIOS_PROTOCOL         *This,
  IN UDC_ATTRIBUTES                   Attributes,
  IN UINTN                            BbsEntry,
  IN VOID                             *BeerData,
  IN VOID                             *ServiceAreaData
  );


/**
  Load a legacy PC-AT OPROM on the PciHandle device. Return information
  about how many disks were added by the OPROM and the shadow address and
  size. DiskStart & DiskEnd are INT 13h drive letters. Thus 0x80 is C:

  @param  This                   Protocol instance pointer.
  @param  PciHandle              The PCI PC-AT OPROM from this devices ROM BAR will
                                 be loaded. This value is NULL if RomImage is
                                 non-NULL. This is the normal case.
  @param  RomImage               A PCI PC-AT ROM image. This argument is non-NULL
                                 if there is no hardware associated with the ROM
                                 and thus no PciHandle, otherwise is must be NULL.
                                 Example is PXE base code.
  @param  Flags                  Indicates if ROM found and if PC-AT.
  @param  DiskStart              Disk number of first device hooked by the ROM. If
                                 DiskStart is the same as DiskEnd no disked were
                                 hooked.
  @param  DiskEnd                Disk number of the last device hooked by the ROM.
  @param  RomShadowAddress       Shadow address of PC-AT ROM
  @param  RomShadowedSize        Size of RomShadowAddress in bytes

  @retval EFI_SUCCESS            Legacy ROM loaded for this device
  @retval EFI_INVALID_PARAMETER  PciHandle not found
  @retval EFI_UNSUPPORTED        There is no PCI ROM in the ROM BAR or no onboard
                                 ROM

**/
EFI_STATUS
EFIAPI
LegacyBiosInstallPciRom (
  IN  EFI_LEGACY_BIOS_PROTOCOL          * This,
  IN  EFI_HANDLE                        PciHandle,
  IN  VOID                              **RomImage,
  OUT UINTN                             *Flags,
  OUT UINT8                             *DiskStart, OPTIONAL
  OUT UINT8                             *DiskEnd, OPTIONAL
  OUT VOID                              **RomShadowAddress, OPTIONAL
  OUT UINT32                            *RomShadowedSize OPTIONAL
  );


/**
  Fill in the standard BDA for Keyboard LEDs

  @param  This                   Protocol instance pointer.
  @param  Leds                   Current LED status

  @retval EFI_SUCCESS            It should always work.

**/
EFI_STATUS
EFIAPI
LegacyBiosUpdateKeyboardLedStatus (
  IN EFI_LEGACY_BIOS_PROTOCOL           *This,
  IN UINT8                              Leds
  );


/**
  Get all BBS info

  @param  This                   Protocol instance pointer.
  @param  HddCount               Number of HDD_INFO structures
  @param  HddInfo                Onboard IDE controller information
  @param  BbsCount               Number of BBS_TABLE structures
  @param  BbsTable               List BBS entries

  @retval EFI_SUCCESS            Tables returned
  @retval EFI_NOT_FOUND          resource not found
  @retval EFI_DEVICE_ERROR       can not get BBS table

**/
EFI_STATUS
EFIAPI
LegacyBiosGetBbsInfo (
  IN  EFI_LEGACY_BIOS_PROTOCOL          *This,
  OUT UINT16                            *HddCount,
  OUT HDD_INFO                          **HddInfo,
  OUT UINT16                            *BbsCount,
  OUT BBS_TABLE                         **BbsTable
  );


/**
  Shadow all legacy16 OPROMs that haven't been shadowed.
  Warning: Use this with caution. This routine disconnects all EFI
  drivers. If used externally then caller must re-connect EFI
  drivers.

  @param  This                   Protocol instance pointer.

  @retval EFI_SUCCESS            OPROMs shadowed

**/
EFI_STATUS
EFIAPI
LegacyBiosShadowAllLegacyOproms (
  IN EFI_LEGACY_BIOS_PROTOCOL   *This
  );


/**
  Attempt to legacy boot the BootOption. If the EFI contexted has been
  compromised this function will not return.

  @param  This                   Protocol instance pointer.
  @param  BbsDevicePath          EFI Device Path from BootXXXX variable.
  @param  LoadOptionsSize        Size of LoadOption in size.
  @param  LoadOptions            LoadOption from BootXXXX variable

  @retval EFI_SUCCESS            Removable media not present

**/
EFI_STATUS
EFIAPI
LegacyBiosLegacyBoot (
  IN  EFI_LEGACY_BIOS_PROTOCOL          *This,
  IN  BBS_BBS_DEVICE_PATH               *BbsDevicePath,
  IN  UINT32                            LoadOptionsSize,
  IN  VOID                              *LoadOptions
  );


/**
  Allocate memory < 1 MB and copy the thunker code into low memory. Se up
  all the descriptors.

  @param  Private                Private context for Legacy BIOS

  @retval EFI_SUCCESS            Should only pass.

**/
EFI_STATUS
LegacyBiosInitializeThunk (
  IN  LEGACY_BIOS_INSTANCE    *Private
  );


/**
  Fill in the standard BDA and EBDA stuff before Legacy16 load

  @param  Private                Legacy BIOS Instance data

  @retval EFI_SUCCESS            It should always work.

**/
EFI_STATUS
LegacyBiosInitBda (
  IN  LEGACY_BIOS_INSTANCE    *Private
  );


/**
  Collect IDE Inquiry data from the IDE disks

  @param  Private                Legacy BIOS Instance data
  @param  HddInfo                Hdd Information
  @param  Flag                   Reconnect IdeController or not

  @retval EFI_SUCCESS            It should always work.

**/
EFI_STATUS
LegacyBiosBuildIdeData (
  IN  LEGACY_BIOS_INSTANCE      *Private,
  IN  HDD_INFO                  **HddInfo,
  IN  UINT16                    Flag
  );


/**
  Enable ide controller.  This gets disabled when LegacyBoot.c is about
  to run the Option ROMs.

  @param  Private                Legacy BIOS Instance data


**/
VOID
EnableIdeController (
  IN LEGACY_BIOS_INSTANCE       *Private
  );


/**
  If the IDE channel is in compatibility (legacy) mode, remove all
  PCI I/O BAR addresses from the controller.

  @param  IdeController          The handle of target IDE controller


**/
VOID
InitLegacyIdeController (
  IN EFI_HANDLE                 IdeController
  );


/**
  Program the interrupt routing register in all the PCI devices. On a PC AT system
  this register contains the 8259 IRQ vector that matches it's PCI interrupt.

  @param  Private                Legacy  BIOS Instance data

  @retval EFI_SUCCESS            Succeed.
  @retval EFI_ALREADY_STARTED    All PCI devices have been processed.

**/
EFI_STATUS
PciProgramAllInterruptLineRegisters (
  IN  LEGACY_BIOS_INSTANCE      *Private
  );


/**
  Collect EFI Info about legacy devices.

  @param  Private                Legacy BIOS Instance data

  @retval EFI_SUCCESS            It should always work.

**/
EFI_STATUS
LegacyBiosBuildSioData (
  IN  LEGACY_BIOS_INSTANCE      *Private
  );


/**
  Shadow all the PCI legacy ROMs. Use data from the Legacy BIOS Protocol
  to chose the order. Skip any devices that have already have legacy
  BIOS run.

  @param  Private                Protocol instance pointer.

  @retval EFI_SUCCESS            Succeed.
  @retval EFI_UNSUPPORTED        Cannot get VGA device handle.

**/
EFI_STATUS
PciShadowRoms (
  IN  LEGACY_BIOS_INSTANCE      *Private
  );


/**
  Fill in the standard BDA and EBDA stuff prior to legacy Boot

  @param  Private                Legacy BIOS Instance data

  @retval EFI_SUCCESS            It should always work.

**/
EFI_STATUS
LegacyBiosCompleteBdaBeforeBoot (
  IN  LEGACY_BIOS_INSTANCE    *Private
  );


/**
  Fill in the standard CMOS stuff before Legacy16 load

  @param  Private                Legacy BIOS Instance data

  @retval EFI_SUCCESS            It should always work.

**/
EFI_STATUS
LegacyBiosInitCmos (
  IN  LEGACY_BIOS_INSTANCE    *Private
  );


/**
  Fill in the standard CMOS stuff prior to legacy Boot

  @param  Private                Legacy BIOS Instance data

  @retval EFI_SUCCESS            It should always work.

**/
EFI_STATUS
LegacyBiosCompleteStandardCmosBeforeBoot (
  IN  LEGACY_BIOS_INSTANCE    *Private
  );


/**
  Contains the code that is copied into low memory (below 640K).
  This code reflects interrupts 0x68-0x6f to interrupts 0x08-0x0f.
  This template must be copied into low memory, and the IDT entries
  0x68-0x6F must be point to the low memory copy of this code.  Each
  entry is 4 bytes long, so IDT entries 0x68-0x6F can be easily
  computed.

**/
VOID
InterruptRedirectionTemplate (
  VOID
  );


/**
  Build the E820 table.

  @param  Private                Legacy BIOS Instance data
  @param  Size                   Size of E820 Table

  @retval EFI_SUCCESS            It should always work.

**/
EFI_STATUS
LegacyBiosBuildE820 (
  IN  LEGACY_BIOS_INSTANCE    *Private,
  OUT UINTN                   *Size
  );

/**
  This function is to put all AP in halt state.

  @param  Private                Legacy BIOS Instance data

**/
VOID
ShutdownAPs (
  IN LEGACY_BIOS_INSTANCE              *Private
  );

/**
  Worker function for LegacyBiosGetFlatDescs, retrieving content of
  specific registers.

  @param  IntThunk  Pointer to IntThunk of Legacy BIOS context.

**/
VOID
GetRegisters (
  LOW_MEMORY_THUNK    *IntThunk
  );

/**
  Routine for calling real thunk code.

  @param  RealCode    The address of thunk code.
  @param  BiosInt     The Bios interrupt vector number.
  @param  CallAddress The address of 16-bit mode call.

  @return  Status returned by real thunk code

**/
UINTN
CallRealThunkCode (
  UINT8               *RealCode,
  UINT8               BiosInt,
  UINT32              CallAddress
  );

/**
  Routine for generating soft interrupt.

  @param Vector  The interrupt vector number.

**/
VOID
GenerateSoftInit (
  UINT8               Vector
  );

/**
  Do an AllocatePages () of type AllocateMaxAddress for EfiBootServicesCode
  memory.

  @param  AllocateType               Allocated Legacy Memory Type
  @param  StartPageAddress           Start address of range
  @param  Pages                      Number of pages to allocate
  @param  Result                     Result of allocation

  @retval EFI_SUCCESS                Legacy16 code loaded
  @retval Other                      No protocol installed, unload driver.

**/
EFI_STATUS
AllocateLegacyMemory (
  IN  EFI_ALLOCATE_TYPE         AllocateType,
  IN  EFI_PHYSICAL_ADDRESS      StartPageAddress,
  IN  UINTN                     Pages,
  OUT EFI_PHYSICAL_ADDRESS      *Result
  );

/**
  Get a region from the LegacyBios for Tiano usage. Can only be invoked once.

  @param  This                       Protocol instance pointer.
  @param  LegacyMemorySize           Size of required region
  @param  Region                     Region to use. 00 = Either 0xE0000 or 0xF0000
                                     block Bit0 = 1 0xF0000 block Bit1 = 1 0xE0000
                                     block
  @param  Alignment                  Address alignment. Bit mapped. First non-zero
                                     bit from right is alignment.
  @param  LegacyMemoryAddress        Region Assigned

  @retval EFI_SUCCESS                Region assigned
  @retval EFI_ACCESS_DENIED          Procedure previously invoked
  @retval Other                      Region not assigned

**/
EFI_STATUS
EFIAPI
LegacyBiosGetLegacyRegion (
  IN    EFI_LEGACY_BIOS_PROTOCOL *This,
  IN    UINTN                    LegacyMemorySize,
  IN    UINTN                    Region,
  IN    UINTN                    Alignment,
  OUT   VOID                     **LegacyMemoryAddress
  );

/**
  Get a region from the LegacyBios for Tiano usage. Can only be invoked once.

  @param  This                       Protocol instance pointer.
  @param  LegacyMemorySize           Size of data to copy
  @param  LegacyMemoryAddress        Legacy Region destination address Note: must
                                     be in region assigned by
                                     LegacyBiosGetLegacyRegion
  @param  LegacyMemorySourceAddress  Source of data

  @retval EFI_SUCCESS                Region assigned
  @retval EFI_ACCESS_DENIED          Destination outside assigned region

**/
EFI_STATUS
EFIAPI
LegacyBiosCopyLegacyRegion (
  IN EFI_LEGACY_BIOS_PROTOCOL *This,
  IN    UINTN                 LegacyMemorySize,
  IN    VOID                  *LegacyMemoryAddress,
  IN    VOID                  *LegacyMemorySourceAddress
  );

/**
  Find Legacy16 BIOS image in the FLASH device and shadow it into memory. Find
  the $EFI table in the shadow area. Thunk into the Legacy16 code after it had
  been shadowed.

  @param  Private                    Legacy BIOS context data

  @retval EFI_SUCCESS                Legacy16 code loaded
  @retval Other                      No protocol installed, unload driver.

**/
EFI_STATUS
ShadowAndStartLegacy16 (
  IN  LEGACY_BIOS_INSTANCE  *Private
  );

/**
  Checks the state of the floppy and if media is inserted.
  
  This routine checks the state of the floppy and if media is inserted.
  There are 3 cases:
  No floppy present         - Set BBS entry to ignore
  Floppy present & no media - Set BBS entry to lowest priority. We cannot
  set it to ignore since 16-bit CSM will
  indicate no floppy and thus drive A: is
  unusable. CSM-16 will not try floppy since
  lowest priority and thus not incur boot
  time penality.
  Floppy present & media    - Set BBS entry to some priority.

  @return  State of floppy media

**/
UINT8
HasMediaInFloppy (
  VOID
  );

/**
  Identify drive data must be updated to actual parameters before boot.
  This requires updating the checksum, if it exists.

  @param  IdentifyDriveData       ATA Identify Data
  @param  Checksum                checksum of the ATA Identify Data

  @retval EFI_SUCCESS             checksum calculated
  @retval EFI_SECURITY_VIOLATION  IdentifyData invalid

**/
EFI_STATUS
CalculateIdentifyDriveChecksum (
  IN  UINT8     *IdentifyDriveData,
  OUT UINT8     *Checksum
  );

/**
  Identify drive data must be updated to actual parameters before boot.

  @param  IdentifyDriveData       ATA Identify Data

**/
VOID
UpdateIdentifyDriveData (
  IN  UINT8     *IdentifyDriveData
  );

/**
  Complete build of BBS TABLE.

  @param  Private                 Legacy BIOS Instance data
  @param  BbsTable                BBS Table passed to 16-bit code

  @retval EFI_SUCCESS             Removable media not present

**/
EFI_STATUS
LegacyBiosBuildBbs (
  IN  LEGACY_BIOS_INSTANCE      *Private,
  IN  BBS_TABLE                 *BbsTable
  );

/**
  Read CMOS register through index/data port.

  @param[in]  Index   The index of the CMOS register to read.

  @return  The data value from the CMOS register specified by Index.

**/
UINT8
LegacyReadStandardCmos (
  IN UINT8  Index
  );

/**
  Write CMOS register through index/data port.

  @param[in]  Index  The index of the CMOS register to write.
  @param[in]  Value  The value of CMOS register to write.

  @return  The value written to the CMOS register specified by Index.

**/
UINT8
LegacyWriteStandardCmos (
  IN UINT8  Index,
  IN UINT8  Value
  );

/**
  Calculate the new standard CMOS checksum and write it.

  @param  Private      Legacy BIOS Instance data

  @retval EFI_SUCCESS  Calculate 16-bit checksum successfully

**/
EFI_STATUS
LegacyCalculateWriteStandardCmosChecksum (
  VOID
  );

/**
  Test to see if a legacy PCI ROM exists for this device. Optionally return
  the Legacy ROM instance for this PCI device.

  @param[in]  This                   Protocol instance pointer.
  @param[in]  PciHandle              The PCI PC-AT OPROM from this devices ROM BAR will be loaded
  @param[out] RomImage               Return the legacy PCI ROM for this device
  @param[out] RomSize                Size of ROM Image
  @param[out] RuntimeImageLength     Runtime size of ROM Image
  @param[out] Flags                  Indicates if ROM found and if PC-AT.
  @param[out] OpromRevision          Revision of the PCI Rom
  @param[out] ConfigUtilityCodeHeaderPointer of Configuration Utility Code Header

  @return EFI_SUCCESS            Legacy Option ROM availible for this device
  @return EFI_ALREADY_STARTED    This device is already managed by its Oprom
  @return EFI_UNSUPPORTED        Legacy Option ROM not supported.

**/
EFI_STATUS
LegacyBiosCheckPciRomEx (
  IN EFI_LEGACY_BIOS_PROTOCOL           *This,
  IN  EFI_HANDLE                        PciHandle,
  OUT VOID                              **RomImage, OPTIONAL
  OUT UINTN                             *RomSize, OPTIONAL
  OUT UINTN                             *RuntimeImageLength, OPTIONAL
  OUT UINTN                             *Flags, OPTIONAL
  OUT UINT8                             *OpromRevision, OPTIONAL
  OUT VOID                              **ConfigUtilityCodeHeader OPTIONAL
  );

/**
  Relocate this image under 4G memory for IPF.

  @param  ImageHandle  Handle of driver image.
  @param  SystemTable  Pointer to system table.

  @retval EFI_SUCCESS  Image successfully relocated.
  @retval EFI_ABORTED  Failed to relocate image.

**/
EFI_STATUS
RelocateImageUnder4GIfNeeded (
  IN EFI_HANDLE           ImageHandle,
  IN EFI_SYSTEM_TABLE     *SystemTable
  );

/**
  Thunk to 16-bit real mode and call Segment:Offset. Regs will contain the
  16-bit register context on entry and exit. Arguments can be passed on
  the Stack argument

  @param  This       Protocol instance pointer.
  @param  Segment    Segemnt of 16-bit mode call
  @param  Offset     Offset of 16-bit mdoe call
  @param  Regs       Register contexted passed into (and returned) from thunk to
                     16-bit mode
  @param  Stack      Caller allocated stack used to pass arguments
  @param  StackSize  Size of Stack in bytes

  @retval FALSE      Thunk completed, and there were no BIOS errors in the target code.
                     See Regs for status.
  @retval TRUE       There was a BIOS erro in the target code.

**/
BOOLEAN
EFIAPI
InternalLegacyBiosFarCall (
  IN  EFI_LEGACY_BIOS_PROTOCOL        *This,
  IN  UINT16                          Segment,
  IN  UINT16                          Offset,
  IN  EFI_IA32_REGISTER_SET           *Regs,
  IN  VOID                            *Stack,
  IN  UINTN                           StackSize
  );

/**
  Load a legacy PC-AT OpROM for VGA controller.

  @param  Private                Driver private data.

  @retval EFI_SUCCESS            Legacy ROM successfully installed for this device.
  @retval EFI_DEVICE_ERROR       No VGA device handle found, or native EFI video
                                 driver cannot be successfully disconnected, or VGA
                                 thunk driver cannot be successfully connected.

**/
EFI_STATUS
LegacyBiosInstallVgaRom (
  IN  LEGACY_BIOS_INSTANCE            *Private
  );

#endif