...
//SD_Disable();
SD_Enable();
FRESULT res = f_mount( &FileSystem, "", 1 );
...
u32 IWRAM_CODE Read_SD_sectors(u32 address,u16 count,u8* SDbuffer)
{
SetRompage(0x8000);//change to OS mode
SD_Enable();
...
SD_Disable();
SetRompage(0x200);//return to game...