Access to SD-card from µController AND from USB possible?

Hello,
I tried this in a slightly different way, still without success.
Access to the SD-Card via USB works as expected.

I took the example "USB device Mass Storage (MBC4300)" and modified the mail loop:

finit              ("M0:");           /* Initialize SD Card 0               */
fmount             ("M0:");           /* Mount SD Card 0                    */
USBD_Initialize    (0);               /* USB Device 0 Initialization        */
USBD_Connect       (0);               /* USB Device 0 Connect               */
while (1) {
  osDelay(10);

  // added code start:
  if(button_pressed() ) {
    USBD_Disconnect (0);
    USBD_Uninitialize(0); // this fails, stays in an endless loop, see below
    f=fopen("M0:test4.txt","a");
    fprintf(f,"data written\n");
    fclose (f);
    USBD_Initialize(0);
    USBD_Connect(0);
  }
  // added code end
}

USBD_Uninitialize(0) never returns:
in file USBD0_LPC43xx.c:

 // Disable USB0 register interface clock
 LPC_CCU1->CLK_M4_USB1_CFG &= ~1;
 while (LPC_CCU1->CLK_M4_USB0_STAT & 1); // endless loop here

If USBD_Uninitialize(0) would not fail:
Could this method (disconnect/disable USB to allow write access to SD-Card from firmware) work?

Any idea why USBD_Uninitialize() fails?

Without the surrounding USBD_Uninitialize()/USBD_Initialize() the code is executed, fopen() and fprintf() and fclose() do not return any errors, but the file on the SD-card is not modified.

int main (void) {

  GLCD_Initialize         ();
  GLCD_SetBackgroundColor (GLCD_COLOR_BLUE);
  GLCD_SetForegroundColor (GLCD_COLOR_WHITE);
  GLCD_ClearScreen        ();
  GLCD_SetFont            (&GLCD_Font_16x24);
  GLCD_DrawString         (0, 0*24, "    USB Device      ");
  GLCD_DrawString         (0, 1*24, "    MSC Class       ");
  GLCD_DrawString         (0, 2*24, "Mass Storage Example");
  GLCD_DrawString         (0, 4*24, "USB0: SD Card Disk  ");
  GLCD_DrawString         (0, 5*24, "USB1: Memory Disk   ");
  GLCD_DrawString         (0, 8*24, "  Keil Tools by ARM ");
  GLCD_DrawString         (0, 9*24, "    http://www.keil.com    ");

  Buttons_Initialize();
  finit              ("M0:");
  fmount             ("M0:");
  USBD_Initialize    (0);
  USBD_Connect       (0);               /* USB Device 0 Connect               */

  funmount             ("M0:");   //  x1 
  finit              ("M0:");
  fmount             ("M0:");
  f=fopen("M0:test1.txt","w");      // erzeuge leere datei
  fprintf(f,"Hello SD-Card!\n");
  fflush(f);
  fclose (f);
  funmount             ("M0:");  //  x2   
  finit              ("M0:");
  fmount             ("M0:");

  while (1) {
    static int button;
    osDelay(10);
    button<<=1;
    button|=(Buttons_GetState()&1);
    if(button==1)
    {
      funmount           ("M0:"); //  x3
      finit              ("M0:");
      fmount             ("M0:");
      f=fopen("M0:test2.txt","a");
      fprintf(f,"Hello Test %d!\n",n++);
      fflush(f);
      fclose (f);
      funmount             ("M0:");   //  x4 
      finit              ("M0:");
      fmount             ("M0:");
    }
  }
}

x1:
I think this unmout(), init(), mount() sequence might be required because:
"USBD_Initialize()" calles the function "USBD_MSC0_Initialize()".
In this file I find the following code line:

usbd_msc0_media_own = MEDIA_OWN_USB;  // Initially media is owned by USB

I want to access the sdcard via fopen(), fprintf() fclose() therefor I want to totally "disconnect" the usb-connection.

x2: If I omit this, the following fprintf-sequence (when the button is pressed) writes another file "test2.txt", but the first file "test1.txt" gets sometimes corrupted.

x3: same reason as x1
x4: not sure if it is required...

Refer also to:
www.keil.com/.../group__usbd__msc_functions.html
under headline: Media Ownership

Let us know if you have further questions.
Reinhard