INFO: Tips for Porting Windows NT TAPI Service Providers to Windows CE (290209)

MORE INFORMATION

• TAPI response to the TSP LINE_CREATE message
  
  Windows NT TAPI calls TSPI_providerCreateLineDevice in response to a TAPI service provider LINE_CREATE message. Windows CE TAPI does not call TSPI_providerCreateLineDevice. In Windows CE, TAPI treats dwParam2 as a pointer to a DWORD which will receive the TAPI assigned line device identifier. TAPI assigns this ID before it returns to the TSP. When a TSP wants to create a new line device in Windows CE, it is sufficient to simply send a LINE_CREATE message.
• TSPI_providerCreateLineDevice parameters
  
  TSPI_providerCreateLineDevice parameters are different in Windows CE than Windows NT. For Windows CE, the function prototype is:

  LONG
  TSPI_providerCreateLineDevice(
             HKEY hActiveKey,
             LPCWSTR lpszDevPath,
             LPCWSTR lpszDeviceName
        );
  
  Returns: TAPI error code
  
  hActiveKey - Open handle to the device's "active" key in the registry.
  lpszDevPath - registry path string to the device's driver key
  lpszDeviceName - the device name (i.e. COM3: )
  						

  On Windows CE, TSPI_providerCreateLineDevice is called when TAPI is notified by the operating system that a new device has been created that has an associated TSP. This is a registry-driven process. A serial device typically has subkeys that describe the associated TSPs. When the device loader sees that a device has an associated TSP, it calls TAPI, passing an open handle to the device's "active" key in the registry, the registry path string to the device's driver key, and the device name. (Note how those correspond directly to the parameters to TSPI_providerCreateLineDevice.)
• Unmatched DLL_PROCESS_ATTACH/DLL_PROCESS_DETACH indications
  
  On Windows CE, the TAPI functions are exported as an API set from the Device.exe protected server library (PSL). The implications of this are that TAPI.dll and the TSP DLLs are loaded only in the Device.exe process. An application thread calling one of the TAPI functions goes through a thunk that switches the thread into the Device.exe PSL and on return thunks back to the application process context. This means a TSP DLL will be loaded once and receive one DLL_PROCESS_ATTACH indication. It will not be unloaded, and therefore there will be no corresponding DLL_PROCESS_DETACH.