Cannot create files with FatFs

Other Hardware Storage
2

For completeness, here is how I've implemented the functions required by FatFs, using SerialFlash:

/*-----------------------------------------------------------------------*/
/* Read Sector(s)                                                        */
/*-----------------------------------------------------------------------*/

DRESULT disk_read (
	BYTE pdrv,		/* Physical drive nmuber to identify the drive */
	BYTE *buff,		/* Data buffer to store read data */
	LBA_t sector,	/* Start sector in LBA */
	UINT count		/* Number of sectors to read */
)
{
  BYTE * b = buff;

  SerialFlash.read(sector * SECTOR_SIZE, b, SECTOR_SIZE * count);

  return RES_OK;
}



/*-----------------------------------------------------------------------*/
/* Write Sector(s)                                                       */
/*-----------------------------------------------------------------------*/

#if FF_FS_READONLY == 0

DRESULT disk_write (
	BYTE pdrv,			/* Physical drive nmuber to identify the drive */
	const BYTE *buff,	/* Data to be written */
	LBA_t sector,		/* Start sector in LBA */
	UINT count			/* Number of sectors to write */
)
{
  BYTE * b = (BYTE*) buff;
  
  SerialFlash.eraseSector(sector * SECTOR_SIZE);
  while(!SerialFlash.ready()); // don't know if useful, just to be sure that every task has done
  SerialFlash.write(sector * SECTOR_SIZE, buff, SECTOR_SIZE * count);
  while (!SerialFlash.ready()) ;

  return RES_OK;
}

#endif


/*-----------------------------------------------------------------------*/
/* Miscellaneous Functions                                               */
/*-----------------------------------------------------------------------*/

DRESULT disk_ioctl (
	BYTE pdrv,		/* Physical drive nmuber (0..) */
	BYTE cmd,		/* Control code */
	void *buff		/* Buffer to send/receive control data */
)
{
  DRESULT res = RES_ERROR;  
  
  uint8_t id[5];
  switch( cmd )
  {
    case CTRL_SYNC :   // Make sure that data has been written  
      while (!SerialFlash.ready());
      res = RES_OK;
      break;
    
    case GET_SECTOR_COUNT : 
      SerialFlash.readID(id);
      *(LBA_t*)buff = SerialFlash.capacity(id) / SECTOR_SIZE;
      res = RES_OK;
      break;  

    case GET_SECTOR_SIZE :
      *(WORD*)buff = SECTOR_SIZE;
      res = RES_OK;
      break;  

    case GET_BLOCK_SIZE :
      *(DWORD*)buff = BLOCK_SIZE;
      res = RES_OK;
      break;  

    default:  
      res = RES_PARERR;  
  }

  return res;
}

The function "SerialFlash::eraseSector" has been taken from here: Erase Sector of Flash using SerialFlash - iotespresso.com