!10 Add a prompt message

Merge pull request !10 from JING/master

source/ff.c

@@ -2658,6 +2658,11 @@ BYTE check_fs (	/* 0:FAT, 2:Valid BS but not FAT, 3:Not a BS, 4:Disk error */
 
 	if (ld_word(fs->win + BS_55AA) != 0xAA55) return 3;	/* Check boot record signature (always here regardless of the sector size) */
 
+	if (!mem_cmp(fs->win + BS_JmpBoot, "\xEB\x76\x90" "EXFAT   ", 11)) {	/* Check if exFAT VBR */
+		PRINTK("exFAT is not supported!\n");
+		return 2;
+	}
+
 	if (fs->win[BS_JmpBoot] == 0xE9 || fs->win[BS_JmpBoot] == 0xEB || fs->win[BS_JmpBoot] == 0xE8) {	/* Valid JumpBoot code? */
 		if (!mem_cmp(fs->win + BS_FilSysType, "FAT", 3)) return 0;		/* Is it an FAT VBR? */
 		if (!mem_cmp(fs->win + BS_FilSysType32, "FAT32", 5)) return 0;	/* Is it an FAT32 VBR? */