Mounting Problems SD Card and STM32F7 Discovery

I've got some problems with the FATFs library and the STM32F7 Series. I want to connect a SD-Card (32GB, SanDisk, FAT32) with the F746G-Discovery-Board to save some data on it. (at first .txt-Files, later read .csv Files to visualize some measuring data).

My problem is, that the f_mount function gives me a "FR_OK" but in the next step I can't open a file with f_open. I located the problem by debugging step by step. It's in the ff.c file of the FatFs lib.

 res = find_volume(&path, &fs, mode);


At this point the program stops. jumping into the function the problem is following line

stat = disk_initialize(fs->drv);    /* Initialize the physical drive */


So the SD-Card is not initialized/mounted? But why does the f_mount giving me the FR_OK?

It would be really nice if someone could help. Thanks!

I tried following things:

• formatted SD-Card (exFat,..)
• other Paths
• adjusted clock frequency to 16 MHz for the SD Card

in main:

FIL fil;

FRESULT fr;

FATFS FatFs;

fr=f_mount(&FatFs,(TCHAR const*)SDPath,1);

if(fr!= FR_OK)
{
Error_Handler();
}

else if (fr == FR_OK)
{
char path[13] = "testfile.txt";
fr = f_open(&fil, (char*)path, FA_WRITE | FA_CREATE_ALWAYS);
// File should be created
//here begins the main problem

if ( fr == FR_OK ) // File opened
{
f_printf(&fil, "%d", 1234);
}
else if (fr != FR_OK)
{
Error_Handler();
}
}

f_close(&fil);
f_mount(0,"SD",0);