MdeModulePkg/Universal/Metronome/Metronome.c

   1 /** @file
   2   Produces the Metronome Architectural Protocol on top of Timer Library.
   3
   4   This is a generic implementation of the Metronome Architectural Protocol that
   5   layers on top of an instance of the Timer Library.  The Timer Library provides
   6   functions for nanosecond and microsecond delays.  This generic implementation
   7   produces a fixed TickPeriod of 1 100ns unit, and when the WaitForTick() service
   8   is called, the number of ticks passed in is converted to either nanosecond or
   9   microsecond units.  If the number of ticks is small, then nanoseconds are used.
  10   If the number of ticks is large, then microseconds are used.  This prevents
  11   overflows that could occur for long delays if only nanoseconds were used and also
  12   provides the greatest accuracy for small delays.
  13
  14 Copyright (c) 2008 - 2018, Intel Corporation. All rights reserved.<BR>
  15 This program and the accompanying materials
  16 are licensed and made available under the terms and conditions of the BSD License
  17 which accompanies this distribution.  The full text of the license may be found at
  18 http://opensource.org/licenses/bsd-license.php
  19
  20 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  21 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  22
  23 **/
  24
  25 #include "Metronome.h"
  26
  27 //
  28 // Handle for the Metronome Architectural Protocol instance produced by this driver
  29 //
  30 EFI_HANDLE  mMetronomeHandle = NULL;
  31
  32 //
  33 // The Metronome Architectural Protocol instance produced by this driver
  34 //
  35 EFI_METRONOME_ARCH_PROTOCOL mMetronome = {
  36   WaitForTick,
  37   1  // TickPeriod = 1*100 ns units
  38 };
  39
  40 /**
  41   Waits for the specified number of ticks.
  42
  43   This function implements EFI_METRONOME_ARCH_PROTOCOL.WaitForTick().
  44   The WaitForTick() function waits for the number of ticks specified by
  45   TickNumber from a known time source in the platform.  If TickNumber of
  46   ticks are detected, then EFI_SUCCESS is returned.  The actual time passed
  47   between entry of this function and the first tick is between 0 and
  48   TickPeriod 100 nS units.  If you want to guarantee that at least TickPeriod
  49   time has elapsed, wait for two ticks.  This function waits for a hardware
  50   event to determine when a tick occurs.  It is possible for interrupt
  51   processing, or exception processing to interrupt the execution of the
  52   WaitForTick() function.  Depending on the hardware source for the ticks, it
  53   is possible for a tick to be missed.  This function cannot guarantee that
  54   ticks will not be missed.  If a timeout occurs waiting for the specified
  55   number of ticks, then EFI_TIMEOUT is returned.
  56
  57   @param  This             The EFI_METRONOME_ARCH_PROTOCOL instance.
  58   @param  TickNumber       Number of ticks to wait.
  59
  60   @retval EFI_SUCCESS      The wait for the number of ticks specified by TickNumber
  61                            succeeded.
  62   @retval EFI_TIMEOUT      A timeout occurred waiting for the specified number of ticks.
  63
  64 **/
  65 EFI_STATUS
  66 EFIAPI
  67 WaitForTick (
  68   IN EFI_METRONOME_ARCH_PROTOCOL  *This,
  69   IN UINT32                       TickNumber
  70   )
  71 {
  72   //
  73   // Check the value of TickNumber, so a 32-bit overflow can be avoided
  74   // when TickNumber of converted to nanosecond units
  75   //
  76   if (TickNumber < 10000000) {
  77     //
  78     // If TickNumber is small, then use NanoSecondDelay()
  79     //
  80     NanoSecondDelay (TickNumber * 100);
  81   } else {
  82     //
  83     // If TickNumber is large, then use MicroSecondDelay()
  84     //
  85     MicroSecondDelay (TickNumber / 10);
  86   }
  87   return EFI_SUCCESS;
  88 }
  89
  90 /**
  91   The user Entry Point for module Metronome. The user code starts with this function.
  92
  93   @param[in] ImageHandle    The firmware allocated handle for the EFI image.
  94   @param[in] SystemTable    A pointer to the EFI System Table.
  95
  96   @retval EFI_SUCCESS       The entry point is executed successfully.
  97   @retval other             Some error occurs when executing this entry point.
  98
  99 **/
 100 EFI_STATUS
 101 EFIAPI
 102 InstallMetronome (
 103   IN EFI_HANDLE        ImageHandle,
 104   IN EFI_SYSTEM_TABLE  *SystemTable
 105   )
 106 {
 107   EFI_STATUS  Status;
 108
 109   //
 110   // Make sure the Metronome Architectural Protocol is not already installed in the system
 111   //
 112   ASSERT_PROTOCOL_ALREADY_INSTALLED (NULL, &gEfiMetronomeArchProtocolGuid);
 113
 114   //
 115   // Install on a new handle
 116   //
 117   Status = gBS->InstallMultipleProtocolInterfaces (
 118                   &mMetronomeHandle,
 119                   &gEfiMetronomeArchProtocolGuid, &mMetronome,
 120                   NULL
 121                   );
 122   ASSERT_EFI_ERROR (Status);
 123
 124   return Status;
 125 }