From 0c4b273f24d9d4291770a20d392ba3275e29e518 Mon Sep 17 00:00:00 2001
From: Scott Shawcroft <scott.shawcroft@gmail.com>
Date: Thu, 6 Jul 2017 10:45:42 -0700
Subject: [PATCH] atmel-samd: Give the on board flash filesystem a unique
 volume ID. This is useful for identifying filesystem mounts and matching them
 up to hardware.

---
 atmel-samd/main.c    | 10 +++++++++-
 extmod/fsusermount.c |  2 +-
 lib/fatfs/ff.c       |  7 ++++---
 lib/fatfs/ff.h       |  2 +-
 stmhal/main.c        |  3 ++-
 5 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/atmel-samd/main.c b/atmel-samd/main.c
index 563237a3c0..45676a5b44 100644
--- a/atmel-samd/main.c
+++ b/atmel-samd/main.c
@@ -95,7 +95,15 @@ void init_flash_fs(void) {
     if (res == FR_NO_FILESYSTEM) {
         // no filesystem so create a fresh one
 
-        res = f_mkfs("/flash", 0, 0);
+        // XOR the serial number together to create a 32-bit id.
+        uint32_t volume_id = 0;
+        uint32_t* addresses[4] = {(uint32_t *) 0x0080A00C, (uint32_t *) 0x0080A040,
+                                  (uint32_t *) 0x0080A044, (uint32_t *) 0x0080A048};
+        for (int i = 0; i < 4; i++) {
+            volume_id ^= *(addresses[i]);
+        }
+
+        res = f_mkfs("/flash", 0, 0, volume_id);
         // Flush the new file system to make sure its repaired immediately.
         flash_flush();
         if (res != FR_OK) {
diff --git a/extmod/fsusermount.c b/extmod/fsusermount.c
index 5882aba991..62aac8d05d 100644
--- a/extmod/fsusermount.c
+++ b/extmod/fsusermount.c
@@ -122,7 +122,7 @@ fs_user_mount_t *fatfs_mount_mkfs(mp_uint_t n_args, const mp_obj_t *pos_args, mp
             }
         } else if (res == FR_NO_FILESYSTEM && args[1].u_bool) {
 mkfs:
-            res = f_mkfs(vfs->str, 1, 0);
+            res = f_mkfs(vfs->str, 1, 0, 0x12345678);
             if (res != FR_OK) {
 mkfs_error:
                 MP_STATE_PORT(fs_user_mount)[i] = NULL;
diff --git a/lib/fatfs/ff.c b/lib/fatfs/ff.c
index 68c529a287..f4a7c7d8fe 100644
--- a/lib/fatfs/ff.c
+++ b/lib/fatfs/ff.c
@@ -4054,7 +4054,8 @@ FRESULT f_forward (
 FRESULT f_mkfs (
 	const TCHAR* path,	/* Logical drive number */
 	BYTE sfd,			/* Partitioning rule 0:FDISK, 1:SFD */
-	UINT au				/* Size of allocation unit in unit of byte or sector */
+	UINT au,				/* Size of allocation unit in unit of byte or sector */
+	DWORD volume_id
 )
 {
 	static const WORD vst[] = { 1024,   512,  256,  128,   64,    32,   16,    8,    4,    2,   0};
@@ -4218,7 +4219,7 @@ FRESULT f_mkfs (
 	ST_DWORD(tbl + BPB_HiddSec, b_vol);		/* Hidden sectors */
 	n = GET_FATTIME();						/* Use current time as VSN */
 	if (fmt == FS_FAT32) {
-		ST_DWORD(tbl + BS_VolID32, n);		/* VSN */
+		ST_DWORD(tbl + BS_VolID32, volume_id);		/* VSN */
 		ST_DWORD(tbl + BPB_FATSz32, n_fat);	/* Number of sectors per FAT */
 		ST_DWORD(tbl + BPB_RootClus, 2);	/* Root directory start cluster (2) */
 		ST_WORD(tbl + BPB_FSInfo, 1);		/* FSINFO record offset (VBR + 1) */
@@ -4227,7 +4228,7 @@ FRESULT f_mkfs (
 		tbl[BS_BootSig32] = 0x29;			/* Extended boot signature */
 		mem_cpy(tbl + BS_VolLab32, "NO NAME    " "FAT32   ", 19);	/* Volume label, FAT signature */
 	} else {
-		ST_DWORD(tbl + BS_VolID, n);		/* VSN */
+		ST_DWORD(tbl + BS_VolID, volume_id);		/* VSN */
 		ST_WORD(tbl + BPB_FATSz16, n_fat);	/* Number of sectors per FAT */
 		tbl[BS_DrvNum] = 0x80;				/* Drive number */
 		tbl[BS_BootSig] = 0x29;				/* Extended boot signature */
diff --git a/lib/fatfs/ff.h b/lib/fatfs/ff.h
index 31d58b4427..21f01188ca 100644
--- a/lib/fatfs/ff.h
+++ b/lib/fatfs/ff.h
@@ -236,7 +236,7 @@ FRESULT f_getfree (const TCHAR* path, DWORD* nclst, FATFS** fatfs);	/* Get numbe
 FRESULT f_getlabel (const TCHAR* path, TCHAR* label, DWORD* vsn);	/* Get volume label */
 FRESULT f_setlabel (const TCHAR* label);							/* Set volume label */
 FRESULT f_mount (FATFS* fs, const TCHAR* path, BYTE opt);			/* Mount/Unmount a logical drive */
-FRESULT f_mkfs (const TCHAR* path, BYTE sfd, UINT au);				/* Create a file system on the volume */
+FRESULT f_mkfs (const TCHAR* path, BYTE sfd, UINT au, DWORD volume_id);				/* Create a file system on the volume */
 FRESULT f_fdisk (BYTE pdrv, const DWORD szt[], void* work);			/* Divide a physical drive into some partitions */
 int f_putc (TCHAR c, FIL* fp);										/* Put a character to the file */
 int f_puts (const TCHAR* str, FIL* cp);								/* Put a string to the file */
diff --git a/stmhal/main.c b/stmhal/main.c
index 97150ecac9..1615c71fab 100644
--- a/stmhal/main.c
+++ b/stmhal/main.c
@@ -187,7 +187,8 @@ MP_NOINLINE STATIC void init_flash_fs(uint reset_mode) {
         led_state(PYB_LED_R2, 1);
         uint32_t start_tick = HAL_GetTick();
 
-        res = f_mkfs("/flash", 0, 0);
+        // TODO(tannewt): Provide a volume id thats based on the MCU id.
+        res = f_mkfs("/flash", 0, 0, 0x12345678);
         if (res == FR_OK) {
             // success creating fresh LFS
         } else {