long file_fat_read_at(const char *filename, unsigned long pos, void *buffer,
unsigned long maxsize);
long file_fat_read(const char *filename, void *buffer, unsigned long maxsize);
long file_fat_read_at(const char *filename, unsigned long pos, void *buffer,
unsigned long maxsize);
long file_fat_read(const char *filename, void *buffer, unsigned long maxsize);