DOSonChip to VINCULUM 2 usb

Project Description:
We have at present a PCB that uses a DOSonChip unit that we use to store information to a microMC memory card. This is proving to be unpopular so we need to convert this to a USB memory stick instead.
The work will involve redesign of the PCB to replace the Dosonchip with USB and also the a relevant software to drive this. The existing file writing code should work seamlessly with the new USB interface.

All work to be done in C using AVR studio.
We will supply existing design and hardware and will require working and tested prototype in return.
The code should be clean , well commented and bug free.

The USB unit we are using is called VNC2 - Vinculum-II Programmable USB 2.0 Host

Several functions will need to be implemented as follows

FRESULT f_mount (BYTE, FATFS*); /* Mount/Unmount a logical drive */
FRESULT f_open (FIL*, const char*, BYTE); /* Open or create a file */
FRESULT f_read (FIL*, void*, UINT, UINT*); /* Read data from a file */
FRESULT f_write (FIL*, const void*, UINT, UINT*); /* Write data to a file */
FRESULT f_lseek (FIL*, DWORD); /* Move file pointer of a file object */
FRESULT f_close (FIL*); /* Close an open file object */
FRESULT f_opendir (DIR*, const char*); /* Open an existing directory */
FRESULT f_readdir (DIR*, FILINFO*); /* Read a directory item */
FRESULT f_stat (const char*, FILINFO*); /* Get file status */
FRESULT f_getfree (const char*, DWORD*, FATFS**); /* Get number of free clusters on the drive */
FRESULT f_truncate (FIL*); /* Truncate file */
FRESULT f_sync (FIL*); /* Flush cached data of a writing file */
FRESULT f_unlink (const char*); /* Delete an existing file or directory */
FRESULT f_mkdir (const char*); /* Create a new directory */
FRESULT f_chmod (const char*, BYTE, BYTE); /* Change file/dir attriburte */
FRESULT f_utime (const char*, const FILINFO*); /* Change file/dir timestamp */
FRESULT f_rename (const char*, const char*); /* Rename/Move a file or directory */
FRESULT f_mkfs (BYTE, BYTE, WORD);