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 SPDX-License-Identifier: BSD-2-Clause-Patent
  16
  17 **/
  18
  19 #include "Metronome.h"
  20
  21 //
  22 // Handle for the Metronome Architectural Protocol instance produced by this driver
  23 //
  24 EFI_HANDLE  mMetronomeHandle = NULL;
  25
  26 //
  27 // The Metronome Architectural Protocol instance produced by this driver
  28 //
  29 EFI_METRONOME_ARCH_PROTOCOL mMetronome = {
  30   WaitForTick,
  31   1  // TickPeriod = 1*100 ns units
  32 };
  33
  34 /**
  35   Waits for the specified number of ticks.
  36
  37   This function implements EFI_METRONOME_ARCH_PROTOCOL.WaitForTick().
  38   The WaitForTick() function waits for the number of ticks specified by
  39   TickNumber from a known time source in the platform.  If TickNumber of
  40   ticks are detected, then EFI_SUCCESS is returned.  The actual time passed
  41   between entry of this function and the first tick is between 0 and
  42   TickPeriod 100 nS units.  If you want to guarantee that at least TickPeriod
  43   time has elapsed, wait for two ticks.  This function waits for a hardware
  44   event to determine when a tick occurs.  It is possible for interrupt
  45   processing, or exception processing to interrupt the execution of the
  46   WaitForTick() function.  Depending on the hardware source for the ticks, it
  47   is possible for a tick to be missed.  This function cannot guarantee that
  48   ticks will not be missed.  If a timeout occurs waiting for the specified
  49   number of ticks, then EFI_TIMEOUT is returned.
  50
  51   @param  This             The EFI_METRONOME_ARCH_PROTOCOL instance.
  52   @param  TickNumber       Number of ticks to wait.
  53
  54   @retval EFI_SUCCESS      The wait for the number of ticks specified by TickNumber
  55                            succeeded.
  56   @retval EFI_TIMEOUT      A timeout occurred waiting for the specified number of ticks.
  57
  58 **/
  59 EFI_STATUS
  60 EFIAPI
  61 WaitForTick (
  62   IN EFI_METRONOME_ARCH_PROTOCOL  *This,
  63   IN UINT32                       TickNumber
  64   )
  65 {
  66   //
  67   // Check the value of TickNumber, so a 32-bit overflow can be avoided
  68   // when TickNumber of converted to nanosecond units
  69   //
  70   if (TickNumber < 10000000) {
  71     //
  72     // If TickNumber is small, then use NanoSecondDelay()
  73     //
  74     NanoSecondDelay (TickNumber * 100);
  75   } else {
  76     //
  77     // If TickNumber is large, then use MicroSecondDelay()
  78     //
  79     MicroSecondDelay (TickNumber / 10);
  80   }
  81   return EFI_SUCCESS;
  82 }
  83
  84 /**
  85   The user Entry Point for module Metronome. The user code starts with this function.
  86
  87   @param[in] ImageHandle    The firmware allocated handle for the EFI image.
  88   @param[in] SystemTable    A pointer to the EFI System Table.
  89
  90   @retval EFI_SUCCESS       The entry point is executed successfully.
  91   @retval other             Some error occurs when executing this entry point.
  92
  93 **/
  94 EFI_STATUS
  95 EFIAPI
  96 InstallMetronome (
  97   IN EFI_HANDLE        ImageHandle,
  98   IN EFI_SYSTEM_TABLE  *SystemTable
  99   )
 100 {
 101   EFI_STATUS  Status;
 102
 103   //
 104   // Make sure the Metronome Architectural Protocol is not already installed in the system
 105   //
 106   ASSERT_PROTOCOL_ALREADY_INSTALLED (NULL, &gEfiMetronomeArchProtocolGuid);
 107
 108   //
 109   // Install on a new handle
 110   //
 111   Status = gBS->InstallMultipleProtocolInterfaces (
 112                   &mMetronomeHandle,
 113                   &gEfiMetronomeArchProtocolGuid, &mMetronome,
 114                   NULL
 115                   );
 116   ASSERT_EFI_ERROR (Status);
 117
 118   return Status;
 119 }