DXE 其它服务

EDKII 中实现DXE Foundation 的源代码位于MdeModulePkg\Core\Dxe 目录下。

/**
Introduces a fine-grained stall.

@param Microseconds The number of microseconds to stall execution.

@retval EFI_SUCCESS Execution was stalled for at least the requested
amount of microseconds.
@retval EFI_NOT_AVAILABLE_YET gMetronome is not available yet

**/
EFI_STATUS
EFIAPI
CoreStall (
IN UINTN Microseconds
)
{
UINT64 Counter;
UINT32 Remainder;
UINTN Index;

if (gMetronome == NULL) {
return EFI_NOT_AVAILABLE_YET;
}

//
// Counter = Microseconds * 10 / gMetronome->TickPeriod
// 0x1999999999999999 = (2^64 - 1) / 10
//
if ((UINT64) Microseconds > 0x1999999999999999ULL) {
    //
    // Microseconds is too large to multiple by 10 first. Perform the divide
    // operation first and loop 10 times to avoid 64-bit math overflow.
    //
    Counter = DivU64x32Remainder (
                Microseconds,
                gMetronome->TickPeriod,
                &Remainder
                );
    for (Index = 0; Index < 10; Index++) {
      CoreInternalWaitForTick (Counter);
    }

    if (Remainder != 0) {
      //
      // If Remainder was not zero, then normally, Counter would be rounded
      // up by 1 tick. In this case, since a loop for 10 counts was used
      // to emulate the multiply by 10 operation, Counter needs to be rounded
      // up by 10 counts.
      //
      CoreInternalWaitForTick (10);
    }
} else {
    //
    // Calculate the number of ticks by dividing the number of microseconds by
    // the TickPeriod. Calculation is based on 100ns unit.
    //
    Counter = DivU64x32Remainder (
                MultU64x32 (Microseconds, 10),
                gMetronome->TickPeriod,
                &Remainder
                );
    if (Remainder != 0) {
      //
      // If Remainder is not zero, then round Counter up by one tick.
      //
      Counter++;
    }
    CoreInternalWaitForTick (Counter);
}

return EFI_SUCCESS;
}

CoreStall() 实现了UEFI 规范中定义的Stall 服务。它的功能非常简单，就是使得运行中的程序

进行一段时间的延时，该延时是以微秒（micro-second) 为单位的。由于每种平台用于计时的芯片

组硬件是不同的而DXE Croe 的实现又要求独立于平台特性。

EFI_STATUS
EFIAPI
CoreInstallConfigurationTable (
IN EFI_GUID *Guid,
IN VOID *Table
)
{
UINTN Index;
EFI_CONFIGURATION_TABLE *EfiConfigurationTable;
EFI_CONFIGURATION_TABLE *OldTable;

//
// If Guid is NULL, then this operation cannot be performed
//
if (Guid == NULL) {
return EFI_INVALID_PARAMETER;
}

EfiConfigurationTable = gDxeCoreST->ConfigurationTable;

//
// Search all the table for an entry that matches Guid
//
for (Index = 0; Index < gDxeCoreST->NumberOfTableEntries; Index++) {
    if (CompareGuid (Guid, &(gDxeCoreST->ConfigurationTable[Index].VendorGuid))) {
      break;
    }
}

该函数的功能为向EFI 系统表（EFI System Table）中加入，更新或者删除一个配置表。UEFI

规范中定义了该系统表的结构，其中有一个指向配置表数组的指针ConfiguraitonTable; 该指针

指向了一系列以EFI_GUID 为标识的配置表，这些配置表的个数由系统表中的NumberOfTableEntries 来

指定。

通过Configuration 和NumberOfTableEntries 来遍历系统表中已经存的配置表，找寻输入的GUID

所对应的配置表。

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