Technical Document #41

Note: Beginning with version 6.00 of WinDriver, for Contiguous Buffer DMA allocation WD_DMALock() also returns the kernel mapping of the allocated buffer - within dma.pKernelAddr. In previous versions of WinDriver, the kernel address was not obtainable via WD_DMALock() and there was need in an additional step, calling  WD_CardRegister(). 

You can access the allocated memory from your user mode application using the returned user mode mapped address (dma.pUserAddr) as if it was the result of a malloc() call. 

To access the shared memory buffer from the Kernel PlugIn application, you need to pass the kernel mapping of the allocated buffer to the Kernel PlugIn. This address is returned by WD_DMALock() in dma.pKernelAddr. 

[Do not try to access the kernel mapped address directly in the user mode. Since this is a kernel mode address, you will generate a protection violation exception if you try to access it from the user mode. For direct user mode access, use the user mode mapping - dma.pUserAddr].

Now you should pass the kernel virtual address to the Kernel PlugIn.
In order to do this, create a WD_KERNEL_PLUGIN_CALL structure and set the pData field to hold the virtual kernel address - dma.pKernelAddr.

You can then pass this structure to the Kernel PlugIn in one of the following ways:

1. A call to WD_KernelPlugInCall(). In this case you will be able to access the kernel virtual address address from within the KP_Call() call-back function in the Kernel PlugIn.
2. A call to WD_IntEnable() \ InterruptEnable() (or InterruptThreadEnable() - in version 5.22 and below). In this case, in the user mode you will store the WD_KERNEL_PLUGIN_CALL structure in the kpCall field of the WD_INTERRUPT structure that is passed to the function. You will then be able to access the kernel virtual address from within the KP_IntEnable() call-back function in the Kernel PlugIn.

Note: The access to the common buffer is not synchronized by WinDriver. You may add access synchronization.

 
  *********************************************************************

  // sample user mode code:

  HANDLE hWD;
  WD_DMA dma;
  WD_KERNEL_PLUGIN kerPlug;
  WD_KERNEL_PLUGIN_CALL kpCall;
  WD_CARD_REGISTER cardReg;  // For version 5.22 or below
  
  hWD = WD_Open();

  BZERO(dma);
  dma.pUserAddr = NULL;
  dma.dwBytes = 0x10000;  // allocate 16K
  dma.dwOptions = DMA_KERNEL_BUFFER_ALLOC; // kernel contiguous buffer
  WD_DMALock(hWD, &dma);
  if (!dma.hDma)
  {
     printf("failed allocating dma buffer\n");
     // exit
  }
  
  // At this point, dma.pUserAddr holds the 
  // user mode mapping of the allocated memory, 
  // dma.pKernelAddr holds the kernel mapping of  
  // the memory.
  ////////////////////////////////////////////////////////////////

 
  // pass the kernel address to the Kernel PlugIn:

  BZERO (kerPlug);
  kerPlug.pcDriverName = KP_DRIVER_NAME;
  WD_KernelPlugInOpen(hWD, &kerPlug);
  if (!kerPlug.hKernelPlugIn)
  {
      printf("failed opening a handle to the Kernel PlugIn\n");
      // exit
  }

  BZERO (kpCall);
  kpCall.hKernelPlugIn = kerPlug.hKernelPlugIn;
  kpCall.dwMessage = YOUR_MESSAGE;
  kpCall.pData = dma.pKernelAddr;  
  WD_KernelPlugInCall(hWD, &kpCall);
  
  *********************************************************************