[PATCH v3 31/35] OvmfPkg/OvmfXen: Introduce XenTimerDxe

["Anthony PERARD" <anthony.perard@citrix.com>]

"PcAtChipsetPkg/8254TimerDxe" is replaced with a Xen-specific
EFI_TIMER_ARCH_PROTOCOL implementation. Also remove
8259InterruptControllerDxe as it is not used anymore.

This Timer uses the local APIC timer as time source as it can work on
both a Xen PVH guest and an HVM one.

Based on the "PcAtChipsetPkg/8254TimerDxe" implementation.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1689
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---

Notes:
    v3:
    - rebased, SPDX, copyright
    
    v2:
    - Use InitializeApicTimer instead of WriteLocalApicReg
    - rework comments (remove many that don't apply)
    - remove unused includes, and libs
    - have a macro to the timervector.
    - cleanup, copyright
    - rework calculation of TimerCount, value to be use by the APIC timer
    - check for overflow of TimerPeriod, with the apic timer, the period can
      be up to about 42s on Xen (or even higher by changing the DivideValue).

 OvmfPkg/OvmfXen.dsc                 |   3 +-
 OvmfPkg/OvmfXen.fdf                 |   3 +-
 OvmfPkg/XenTimerDxe/XenTimerDxe.inf |  42 ++++
 OvmfPkg/XenTimerDxe/XenTimerDxe.h   | 177 ++++++++++++++
 OvmfPkg/XenTimerDxe/XenTimerDxe.c   | 355 ++++++++++++++++++++++++++++
 5 files changed, 576 insertions(+), 4 deletions(-)
 create mode 100644 OvmfPkg/XenTimerDxe/XenTimerDxe.inf
 create mode 100644 OvmfPkg/XenTimerDxe/XenTimerDxe.h
 create mode 100644 OvmfPkg/XenTimerDxe/XenTimerDxe.c

diff --git a/OvmfPkg/OvmfXen.dsc b/OvmfPkg/OvmfXen.dsc
index bc6b6602c6..1ecae3fb45 100644
--- a/OvmfPkg/OvmfXen.dsc
+++ b/OvmfPkg/OvmfXen.dsc
@@ -547,10 +547,9 @@ [Components]
   MdeModulePkg/Universal/SecurityStubDxe/SecurityStubDxe.inf
 
   MdeModulePkg/Universal/EbcDxe/EbcDxe.inf
-  OvmfPkg/8259InterruptControllerDxe/8259.inf
+  OvmfPkg/XenTimerDxe/XenTimerDxe.inf
   UefiCpuPkg/CpuIo2Dxe/CpuIo2Dxe.inf
   UefiCpuPkg/CpuDxe/CpuDxe.inf
-  OvmfPkg/8254TimerDxe/8254Timer.inf
   OvmfPkg/IncompatiblePciDeviceSupportDxe/IncompatiblePciDeviceSupport.inf
   OvmfPkg/PciHotPlugInitDxe/PciHotPlugInit.inf
   MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciHostBridgeDxe.inf {
diff --git a/OvmfPkg/OvmfXen.fdf b/OvmfPkg/OvmfXen.fdf
index 49997fee9b..fa0830a324 100644
--- a/OvmfPkg/OvmfXen.fdf
+++ b/OvmfPkg/OvmfXen.fdf
@@ -298,10 +298,9 @@ [FV.DXEFV]
 INF  MdeModulePkg/Core/RuntimeDxe/RuntimeDxe.inf
 INF  MdeModulePkg/Universal/SecurityStubDxe/SecurityStubDxe.inf
 INF  MdeModulePkg/Universal/EbcDxe/EbcDxe.inf
-INF  OvmfPkg/8259InterruptControllerDxe/8259.inf
+INF  OvmfPkg/XenTimerDxe/XenTimerDxe.inf
 INF  UefiCpuPkg/CpuIo2Dxe/CpuIo2Dxe.inf
 INF  UefiCpuPkg/CpuDxe/CpuDxe.inf
-INF  OvmfPkg/8254TimerDxe/8254Timer.inf
 INF  OvmfPkg/IncompatiblePciDeviceSupportDxe/IncompatiblePciDeviceSupport.inf
 INF  OvmfPkg/PciHotPlugInitDxe/PciHotPlugInit.inf
 INF  MdeModulePkg/Bus/Pci/PciHostBridgeDxe/PciHostBridgeDxe.inf
diff --git a/OvmfPkg/XenTimerDxe/XenTimerDxe.inf b/OvmfPkg/XenTimerDxe/XenTimerDxe.inf
new file mode 100644
index 0000000000..add1d01bbf
--- /dev/null
+++ b/OvmfPkg/XenTimerDxe/XenTimerDxe.inf
@@ -0,0 +1,42 @@
+## @file
+# Local APIC timer driver that provides Timer Arch protocol.
+#
+# Copyright (c) 2005 - 2019, Intel Corporation. All rights reserved.<BR>
+# Copyright (c) 2019, Citrix Systems, Inc.
+#
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = XenTimerDxe
+  FILE_GUID                      = 52fe8196-f9de-4d07-b22f-51f77a0e7c41
+  MODULE_TYPE                    = DXE_DRIVER
+  VERSION_STRING                 = 1.0
+
+  ENTRY_POINT                    = TimerDriverInitialize
+
+[Packages]
+  MdePkg/MdePkg.dec
+  UefiCpuPkg/UefiCpuPkg.dec
+  OvmfPkg/OvmfPkg.dec
+
+[LibraryClasses]
+  UefiBootServicesTableLib
+  BaseLib
+  DebugLib
+  UefiDriverEntryPoint
+  LocalApicLib
+
+[Sources]
+  XenTimerDxe.h
+  XenTimerDxe.c
+
+[Protocols]
+  gEfiCpuArchProtocolGuid       ## CONSUMES
+  gEfiTimerArchProtocolGuid     ## PRODUCES
+[Pcd]
+  gEfiMdePkgTokenSpaceGuid.PcdFSBClock  ## CONSUMES
+[Depex]
+  gEfiCpuArchProtocolGuid
diff --git a/OvmfPkg/XenTimerDxe/XenTimerDxe.h b/OvmfPkg/XenTimerDxe/XenTimerDxe.h
new file mode 100644
index 0000000000..e0a3d95fd0
--- /dev/null
+++ b/OvmfPkg/XenTimerDxe/XenTimerDxe.h
@@ -0,0 +1,177 @@
+/** @file
+  Private data structures
+
+Copyright (c) 2005 - 2018, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2019, Citrix Systems, Inc.
+
+SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#ifndef _TIMER_H_
+#define _TIMER_H_
+
+#include <PiDxe.h>
+
+#include <Protocol/Cpu.h>
+#include <Protocol/Timer.h>
+
+#include <Register/LocalApic.h>
+
+#include <Library/UefiBootServicesTableLib.h>
+#include <Library/BaseLib.h>
+#include <Library/DebugLib.h>
+#include <Library/LocalApicLib.h>
+#include <Library/PcdLib.h>
+
+// The default timer tick duration is set to 10 ms = 100000 100 ns units
+//
+#define DEFAULT_TIMER_TICK_DURATION 100000
+
+//
+// The Timer Vector use for interrupt
+//
+#define LOCAL_APIC_TIMER_VECTOR 32
+
+//
+// Function Prototypes
+//
+/**
+  Initialize the Timer Architectural Protocol driver
+
+  @param ImageHandle     ImageHandle of the loaded driver
+  @param SystemTable     Pointer to the System Table
+
+  @retval EFI_SUCCESS            Timer Architectural Protocol created
+  @retval EFI_OUT_OF_RESOURCES   Not enough resources available to initialize driver.
+  @retval EFI_DEVICE_ERROR       A device error occurred attempting to initialize the driver.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverInitialize (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+;
+
+/**
+
+  This function adjusts the period of timer interrupts to the value specified
+  by TimerPeriod.  If the timer period is updated, then the selected timer
+  period is stored in EFI_TIMER.TimerPeriod, and EFI_SUCCESS is returned.  If
+  the timer hardware is not programmable, then EFI_UNSUPPORTED is returned.
+  If an error occurs while attempting to update the timer period, then the
+  timer hardware will be put back in its state prior to this call, and
+  EFI_DEVICE_ERROR is returned.  If TimerPeriod is 0, then the timer interrupt
+  is disabled.  This is not the same as disabling the CPU's interrupts.
+  Instead, it must either turn off the timer hardware, or it must adjust the
+  interrupt controller so that a CPU interrupt is not generated when the timer
+  interrupt fires.
+
+
+  @param This            The EFI_TIMER_ARCH_PROTOCOL instance.
+  @param NotifyFunction  The rate to program the timer interrupt in 100 nS units.  If
+                         the timer hardware is not programmable, then EFI_UNSUPPORTED is
+                         returned.  If the timer is programmable, then the timer period
+                         will be rounded up to the nearest timer period that is supported
+                         by the timer hardware.  If TimerPeriod is set to 0, then the
+                         timer interrupts will be disabled.
+
+  @retval        EFI_SUCCESS       The timer period was changed.
+  @retval        EFI_UNSUPPORTED   The platform cannot change the period of the timer interrupt.
+  @retval        EFI_DEVICE_ERROR  The timer period could not be changed due to a device error.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverRegisterHandler (
+  IN EFI_TIMER_ARCH_PROTOCOL  *This,
+  IN EFI_TIMER_NOTIFY         NotifyFunction
+  )
+;
+
+/**
+
+  This function adjusts the period of timer interrupts to the value specified
+  by TimerPeriod.  If the timer period is updated, then the selected timer
+  period is stored in EFI_TIMER.TimerPeriod, and EFI_SUCCESS is returned.  If
+  the timer hardware is not programmable, then EFI_UNSUPPORTED is returned.
+  If an error occurs while attempting to update the timer period, then the
+  timer hardware will be put back in its state prior to this call, and
+  EFI_DEVICE_ERROR is returned.  If TimerPeriod is 0, then the timer interrupt
+  is disabled.  This is not the same as disabling the CPU's interrupts.
+  Instead, it must either turn off the timer hardware, or it must adjust the
+  interrupt controller so that a CPU interrupt is not generated when the timer
+  interrupt fires.
+
+
+  @param This            The EFI_TIMER_ARCH_PROTOCOL instance.
+  @param TimerPeriod     The rate to program the timer interrupt in 100 nS units.  If
+                         the timer hardware is not programmable, then EFI_UNSUPPORTED is
+                         returned.  If the timer is programmable, then the timer period
+                         will be rounded up to the nearest timer period that is supported
+                         by the timer hardware.  If TimerPeriod is set to 0, then the
+                         timer interrupts will be disabled.
+
+  @retval        EFI_SUCCESS       The timer period was changed.
+  @retval        EFI_UNSUPPORTED   The platform cannot change the period of the timer interrupt.
+  @retval        EFI_DEVICE_ERROR  The timer period could not be changed due to a device error.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverSetTimerPeriod (
+  IN EFI_TIMER_ARCH_PROTOCOL  *This,
+  IN UINT64                   TimerPeriod
+  )
+;
+
+/**
+
+  This function retrieves the period of timer interrupts in 100 ns units,
+  returns that value in TimerPeriod, and returns EFI_SUCCESS.  If TimerPeriod
+  is NULL, then EFI_INVALID_PARAMETER is returned.  If a TimerPeriod of 0 is
+  returned, then the timer is currently disabled.
+
+
+  @param This            The EFI_TIMER_ARCH_PROTOCOL instance.
+  @param TimerPeriod     A pointer to the timer period to retrieve in 100 ns units.  If
+                         0 is returned, then the timer is currently disabled.
+
+  @retval EFI_SUCCESS            The timer period was returned in TimerPeriod.
+  @retval EFI_INVALID_PARAMETER  TimerPeriod is NULL.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverGetTimerPeriod (
+  IN EFI_TIMER_ARCH_PROTOCOL   *This,
+  OUT UINT64                   *TimerPeriod
+  )
+;
+
+/**
+
+  This function generates a soft timer interrupt. If the platform does not support soft
+  timer interrupts, then EFI_UNSUPPORTED is returned. Otherwise, EFI_SUCCESS is returned.
+  If a handler has been registered through the EFI_TIMER_ARCH_PROTOCOL.RegisterHandler()
+  service, then a soft timer interrupt will be generated. If the timer interrupt is
+  enabled when this service is called, then the registered handler will be invoked. The
+  registered handler should not be able to distinguish a hardware-generated timer
+  interrupt from a software-generated timer interrupt.
+
+
+  @param This              The EFI_TIMER_ARCH_PROTOCOL instance.
+
+  @retval EFI_SUCCESS       The soft timer interrupt was generated.
+  @retval EFI_UNSUPPORTED   The platform does not support the generation of soft timer interrupts.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverGenerateSoftInterrupt (
+  IN EFI_TIMER_ARCH_PROTOCOL  *This
+  )
+;
+
+#endif
diff --git a/OvmfPkg/XenTimerDxe/XenTimerDxe.c b/OvmfPkg/XenTimerDxe/XenTimerDxe.c
new file mode 100644
index 0000000000..9f9e04766c
--- /dev/null
+++ b/OvmfPkg/XenTimerDxe/XenTimerDxe.c
@@ -0,0 +1,355 @@
+/** @file
+  Timer Architectural Protocol as defined in the DXE CIS
+
+Copyright (c) 2005 - 2018, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2019, Citrix Systems, Inc.
+
+SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include "XenTimerDxe.h"
+
+//
+// The handle onto which the Timer Architectural Protocol will be installed
+//
+EFI_HANDLE                mTimerHandle = NULL;
+
+//
+// The Timer Architectural Protocol that this driver produces
+//
+EFI_TIMER_ARCH_PROTOCOL   mTimer = {
+  TimerDriverRegisterHandler,
+  TimerDriverSetTimerPeriod,
+  TimerDriverGetTimerPeriod,
+  TimerDriverGenerateSoftInterrupt
+};
+
+//
+// Pointer to the CPU Architectural Protocol instance
+//
+EFI_CPU_ARCH_PROTOCOL     *mCpu;
+
+//
+// The notification function to call on every timer interrupt.
+// A bug in the compiler prevents us from initializing this here.
+//
+EFI_TIMER_NOTIFY mTimerNotifyFunction;
+
+//
+// The current period of the timer interrupt
+//
+volatile UINT64           mTimerPeriod = 0;
+
+//
+// Worker Functions
+//
+/**
+  Interrupt Handler.
+
+  @param InterruptType    The type of interrupt that occurred
+  @param SystemContext    A pointer to the system context when the interrupt occurred
+**/
+VOID
+EFIAPI
+TimerInterruptHandler (
+  IN EFI_EXCEPTION_TYPE   InterruptType,
+  IN EFI_SYSTEM_CONTEXT   SystemContext
+  )
+{
+  EFI_TPL OriginalTPL;
+
+  OriginalTPL = gBS->RaiseTPL (TPL_HIGH_LEVEL);
+
+  SendApicEoi();
+
+  if (mTimerNotifyFunction != NULL) {
+    //
+    // @bug : This does not handle missed timer interrupts
+    //
+    mTimerNotifyFunction (mTimerPeriod);
+  }
+
+  gBS->RestoreTPL (OriginalTPL);
+}
+
+/**
+
+  This function registers the handler NotifyFunction so it is called every time
+  the timer interrupt fires.  It also passes the amount of time since the last
+  handler call to the NotifyFunction.  If NotifyFunction is NULL, then the
+  handler is unregistered.  If the handler is registered, then EFI_SUCCESS is
+  returned.  If the CPU does not support registering a timer interrupt handler,
+  then EFI_UNSUPPORTED is returned.  If an attempt is made to register a handler
+  when a handler is already registered, then EFI_ALREADY_STARTED is returned.
+  If an attempt is made to unregister a handler when a handler is not registered,
+  then EFI_INVALID_PARAMETER is returned.  If an error occurs attempting to
+  register the NotifyFunction with the timer interrupt, then EFI_DEVICE_ERROR
+  is returned.
+
+
+  @param This             The EFI_TIMER_ARCH_PROTOCOL instance.
+  @param NotifyFunction   The function to call when a timer interrupt fires.  This
+                          function executes at TPL_HIGH_LEVEL.  The DXE Core will
+                          register a handler for the timer interrupt, so it can know
+                          how much time has passed.  This information is used to
+                          signal timer based events.  NULL will unregister the handler.
+
+  @retval        EFI_SUCCESS            The timer handler was registered.
+  @retval        EFI_UNSUPPORTED        The platform does not support timer interrupts.
+  @retval        EFI_ALREADY_STARTED    NotifyFunction is not NULL, and a handler is already
+                                        registered.
+  @retval        EFI_INVALID_PARAMETER  NotifyFunction is NULL, and a handler was not
+                                        previously registered.
+  @retval        EFI_DEVICE_ERROR       The timer handler could not be registered.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverRegisterHandler (
+  IN EFI_TIMER_ARCH_PROTOCOL  *This,
+  IN EFI_TIMER_NOTIFY         NotifyFunction
+  )
+{
+  //
+  // Check for invalid parameters
+  //
+  if (NotifyFunction == NULL && mTimerNotifyFunction == NULL) {
+    return EFI_INVALID_PARAMETER;
+  }
+
+  if (NotifyFunction != NULL && mTimerNotifyFunction != NULL) {
+    return EFI_ALREADY_STARTED;
+  }
+
+  mTimerNotifyFunction = NotifyFunction;
+
+  return EFI_SUCCESS;
+}
+
+/**
+
+  This function adjusts the period of timer interrupts to the value specified
+  by TimerPeriod.  If the timer period is updated, then the selected timer
+  period is stored in EFI_TIMER.TimerPeriod, and EFI_SUCCESS is returned.  If
+  the timer hardware is not programmable, then EFI_UNSUPPORTED is returned.
+  If an error occurs while attempting to update the timer period, then the
+  timer hardware will be put back in its state prior to this call, and
+  EFI_DEVICE_ERROR is returned.  If TimerPeriod is 0, then the timer interrupt
+  is disabled.  This is not the same as disabling the CPU's interrupts.
+  Instead, it must either turn off the timer hardware, or it must adjust the
+  interrupt controller so that a CPU interrupt is not generated when the timer
+  interrupt fires.
+
+
+  @param This            The EFI_TIMER_ARCH_PROTOCOL instance.
+  @param TimerPeriod     The rate to program the timer interrupt in 100 nS units.  If
+                         the timer hardware is not programmable, then EFI_UNSUPPORTED is
+                         returned.  If the timer is programmable, then the timer period
+                         will be rounded up to the nearest timer period that is supported
+                         by the timer hardware.  If TimerPeriod is set to 0, then the
+                         timer interrupts will be disabled.
+
+  @retval        EFI_SUCCESS       The timer period was changed.
+  @retval        EFI_UNSUPPORTED   The platform cannot change the period of the timer interrupt.
+  @retval        EFI_DEVICE_ERROR  The timer period could not be changed due to a device error.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverSetTimerPeriod (
+  IN EFI_TIMER_ARCH_PROTOCOL  *This,
+  IN UINT64                   TimerPeriod
+  )
+{
+  UINT64  TimerCount;
+  UINT32  TimerFrequency;
+  UINTN   DivideValue = 1;
+
+  if (TimerPeriod == 0) {
+    //
+    // Disable timer interrupt for a TimerPeriod of 0
+    //
+    DisableApicTimerInterrupt();
+  } else {
+    TimerFrequency = PcdGet32(PcdFSBClock) / DivideValue;
+
+    //
+    // Convert TimerPeriod into local APIC counts
+    //
+    // TimerPeriod is in 100ns
+    // TimerPeriod/10000000 will be in seconds.
+    TimerCount = DivU64x32 (MultU64x32 (TimerPeriod, TimerFrequency),
+                            10000000);
+
+    // Check for overflow
+    if (TimerCount > MAX_UINT32) {
+      TimerCount = MAX_UINT32;
+      /* TimerPeriod = (MAX_UINT32 / TimerFrequency) * 10000000; */
+      TimerPeriod = 429496730;
+    }
+
+    //
+    // Program the timer with the new count value
+    //
+    InitializeApicTimer(DivideValue, TimerCount, TRUE, LOCAL_APIC_TIMER_VECTOR);
+
+    //
+    // Enable timer interrupt
+    //
+    EnableApicTimerInterrupt();
+  }
+  //
+  // Save the new timer period
+  //
+  mTimerPeriod = TimerPeriod;
+
+  return EFI_SUCCESS;
+}
+
+/**
+
+  This function retrieves the period of timer interrupts in 100 ns units,
+  returns that value in TimerPeriod, and returns EFI_SUCCESS.  If TimerPeriod
+  is NULL, then EFI_INVALID_PARAMETER is returned.  If a TimerPeriod of 0 is
+  returned, then the timer is currently disabled.
+
+
+  @param This            The EFI_TIMER_ARCH_PROTOCOL instance.
+  @param TimerPeriod     A pointer to the timer period to retrieve in 100 ns units.  If
+                         0 is returned, then the timer is currently disabled.
+
+  @retval EFI_SUCCESS            The timer period was returned in TimerPeriod.
+  @retval EFI_INVALID_PARAMETER  TimerPeriod is NULL.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverGetTimerPeriod (
+  IN EFI_TIMER_ARCH_PROTOCOL   *This,
+  OUT UINT64                   *TimerPeriod
+  )
+{
+  if (TimerPeriod == NULL) {
+    return EFI_INVALID_PARAMETER;
+  }
+
+  *TimerPeriod = mTimerPeriod;
+
+  return EFI_SUCCESS;
+}
+
+/**
+
+  This function generates a soft timer interrupt. If the platform does not support soft
+  timer interrupts, then EFI_UNSUPPORTED is returned. Otherwise, EFI_SUCCESS is returned.
+  If a handler has been registered through the EFI_TIMER_ARCH_PROTOCOL.RegisterHandler()
+  service, then a soft timer interrupt will be generated. If the timer interrupt is
+  enabled when this service is called, then the registered handler will be invoked. The
+  registered handler should not be able to distinguish a hardware-generated timer
+  interrupt from a software-generated timer interrupt.
+
+
+  @param This              The EFI_TIMER_ARCH_PROTOCOL instance.
+
+  @retval EFI_SUCCESS       The soft timer interrupt was generated.
+  @retval EFI_UNSUPPORTED   The platform does not support the generation of soft timer interrupts.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverGenerateSoftInterrupt (
+  IN EFI_TIMER_ARCH_PROTOCOL  *This
+  )
+{
+  EFI_TPL     OriginalTPL;
+
+  if (GetApicTimerInterruptState()) {
+    //
+    // Invoke the registered handler
+    //
+    OriginalTPL = gBS->RaiseTPL (TPL_HIGH_LEVEL);
+
+    if (mTimerNotifyFunction != NULL) {
+      //
+      // @bug : This does not handle missed timer interrupts
+      //
+      mTimerNotifyFunction (mTimerPeriod);
+    }
+
+    gBS->RestoreTPL (OriginalTPL);
+  } else {
+    return EFI_UNSUPPORTED;
+  }
+
+  return EFI_SUCCESS;
+}
+
+/**
+  Initialize the Timer Architectural Protocol driver
+
+  @param ImageHandle     ImageHandle of the loaded driver
+  @param SystemTable     Pointer to the System Table
+
+  @retval EFI_SUCCESS            Timer Architectural Protocol created
+  @retval EFI_OUT_OF_RESOURCES   Not enough resources available to initialize driver.
+  @retval EFI_DEVICE_ERROR       A device error occurred attempting to initialize the driver.
+
+**/
+EFI_STATUS
+EFIAPI
+TimerDriverInitialize (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+{
+  EFI_STATUS  Status;
+
+  //
+  // Initialize the pointer to our notify function.
+  //
+  mTimerNotifyFunction = NULL;
+
+  //
+  // Make sure the Timer Architectural Protocol is not already installed in the system
+  //
+  ASSERT_PROTOCOL_ALREADY_INSTALLED (NULL, &gEfiTimerArchProtocolGuid);
+
+  //
+  // Find the CPU architectural protocol.
+  //
+  Status = gBS->LocateProtocol (&gEfiCpuArchProtocolGuid, NULL, (VOID **) &mCpu);
+  ASSERT_EFI_ERROR (Status);
+
+  //
+  // Force the timer to be disabled
+  //
+  Status = TimerDriverSetTimerPeriod (&mTimer, 0);
+  ASSERT_EFI_ERROR (Status);
+
+  //
+  // Install interrupt handler for Local APIC Timer
+  //
+  Status = mCpu->RegisterInterruptHandler (mCpu, LOCAL_APIC_TIMER_VECTOR,
+                                           TimerInterruptHandler);
+  ASSERT_EFI_ERROR (Status);
+
+  //
+  // Force the timer to be enabled at its default period
+  //
+  Status = TimerDriverSetTimerPeriod (&mTimer, DEFAULT_TIMER_TICK_DURATION);
+  ASSERT_EFI_ERROR (Status);
+
+  //
+  // Install the Timer Architectural Protocol onto a new handle
+  //
+  Status = gBS->InstallMultipleProtocolInterfaces (
+                  &mTimerHandle,
+                  &gEfiTimerArchProtocolGuid, &mTimer,
+                  NULL
+                  );
+  ASSERT_EFI_ERROR (Status);
+
+  return Status;
+}
+
-- 
Anthony PERARD