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之前，我们通过修改Shell的代码，能够实现在右上角不断显示当前时间的功能。但是这个方法过于复杂。于是我请教了一下 HZZZ ，看看他是否有什么好办法。

经过他的研究，还是使用定时器的方式不断触发，困难点在于如果退出时没有对应的 Handle，再次触发会导致问题。解决这个问题的方法是：让程序在内存中重新加载自己，跳进去执行之后，最开始的部分就可以丢弃掉了。

当然，如果你想读懂这个程序，要先读懂前面几篇 《Step to UEFI>> 系列的文章。

#include  <Uefi.h>
#include  <Library/UefiLib.h>
#include  <Library/ShellCEntryLib.h>

#include  <stdio.h>
#include  <stdlib.h>
#include  <wchar.h>
#include  <time.h>
#include <Protocol/EfiShell.h>
#include <Library/ShellLib.h>

#include <Protocol/SimpleFileSystem.h>
#include <Protocol/BlockIo.h>
#include <Library/DevicePathLib.h>
#include <Library/HandleParsingLib.h>
#include <Library/SortLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/BaseMemoryLib.h>

#include <Protocol/LoadedImage.h>

extern EFI_BOOT_SERVICES         *gBS;
extern EFI_SYSTEM_TABLE		 *gST;
extern EFI_RUNTIME_SERVICES 	 *gRT;

extern EFI_SHELL_ENVIRONMENT2    *mEfiShellEnvironment2;
extern EFI_HANDLE		  gImageHandle;

STATIC CONST UINTN SecondsToNanoSeconds = 500000;

/**
  The callback function for the timer event used to get map.

  @param[in] Event    The event this function is registered to.
  @param[in] Context  The context registered to the event.
**/
VOID
EFIAPI
Timeout (
  IN EFI_EVENT      Event,
  IN VOID           *Context
  )
{
	EFI_TIME   ET;
	UINTN		x;
	UINTN		y;
  

  //Get cursor postion
  x = gST->ConOut->Mode->CursorColumn;
  y = gST->ConOut->Mode->CursorRow;
  //Move cursor to Up-Left 
  gST -> ConOut -> SetCursorPosition(gST -> ConOut,70,0);  
  //Output current time
  gRT->GetTime(&ET, NULL);  
  Print(L"%2d:%2d:%2d",ET.Hour,ET.Minute,ET.Second);
  //Move cursor back
  gST -> ConOut -> SetCursorPosition(gST -> ConOut,x,y);
  
  return ;
}

typedef struct {
  UINTN                       Signature;
  /// Image handle
  EFI_HANDLE                  Handle;   
  /// Image type
  UINTN                       Type;           
  /// If entrypoint has been called
  BOOLEAN                     Started;        
  /// The image's entry point
  EFI_IMAGE_ENTRY_POINT       EntryPoint;     
  /// loaded image protocol
  EFI_LOADED_IMAGE_PROTOCOL   Info; 
} LOADED_IMAGE_PRIVATE_DATA_TEMP;

#define _CR(Record, TYPE, Field)  ((TYPE *) ((CHAR8 *) (Record) - (CHAR8 *) &(((TYPE *) 0)->Field)))

#define LOADED_IMAGE_PRIVATE_DATA_FROM_THIS(a) \
          _CR(a, LOADED_IMAGE_PRIVATE_DATA_TEMP, Info)



typedef void (*Fun)();

void function()
{
    EFI_STATUS                Status;
    EFI_HANDLE                TimerOne = NULL;
	
    printf("function called\n");
	
    Status  = gBS->CreateEvent (
                    EVT_NOTIFY_SIGNAL | EVT_TIMER,
                    TPL_CALLBACK,
                    Timeout,
                    NULL,
                    &TimerOne
                    );

    if (EFI_ERROR (Status)) {
        Print(L"Create Event Error! \r\n");
		return ;
    }

    Status = gBS->SetTimer (
                   TimerOne,
                   TimerPeriodic,
                   MultU64x32 (SecondsToNanoSeconds, 1)
                   );

    if (EFI_ERROR (Status)) {
        Print(L"Set Timer Error! \r\n");
		return ;
    }
}


int
EFIAPI
main (                                         
  IN int Argc,
  IN char **Argv
  )
{


  EFI_STATUS                         Status = EFI_SUCCESS;
  EFI_LOADED_IMAGE_PROTOCOL          *ImageInfo = NULL;
  EFI_HANDLE                         Handle = 0;
  EFI_GUID                           gEfiLoadedImageProtocolGuid = 
                                     { 0x5B1B31A1, 0x9562, 0x11D2, { 0x8E, 0x3F, 0x00, 0xA0, 0xC9, 0x69, 0x72, 0x3B }};
  LOADED_IMAGE_PRIVATE_DATA_TEMP      *private = NULL;
  Fun                                fun;
  UINTN                              FunOffset;
  UINTN                              FunAddr;

  Status = gBS->HandleProtocol (gImageHandle, &gEfiLoadedImageProtocolGuid, &ImageInfo);
  // function offset in the old image
  FunOffset = (UINTN)function - (UINTN)ImageInfo->ImageBase;

  // load the image in memory again
  Status = gBS->LoadImage(FALSE, gImageHandle, NULL, ImageInfo->ImageBase, (UINTN)ImageInfo->ImageSize, &Handle);  

  // get the newer imageinfo
  Status = gBS->HandleProtocol (Handle, &gEfiLoadedImageProtocolGuid, &ImageInfo);

  private = LOADED_IMAGE_PRIVATE_DATA_FROM_THIS(ImageInfo);
  FunAddr = (UINTN)FunOffset + (UINTN)ImageInfo->ImageBase;
  
  fun = (Fun)((UINTN)FunOffset + (UINTN)ImageInfo->ImageBase);
  // called the newer function in new image,the new image will be always in memory because it will not be free
  fun();
  return EFI_SUCCESS;
}

工作的视频，看得出来这样的方法适应性更好

完整代码下载

ShowTime2