mimxrt: Spend a few words about littlfs file system and MSC access.

robert-hh · robert-hh · commit 8c607f764c34 · 2022-07-05T18:37:53.000+02:00
Since the board may have been formatted with littlfs, the FS device
different when attached to a PC.
diff --git a/docs/mimxrt/quickref.rst b/docs/mimxrt/quickref.rst
@@ -576,6 +576,29 @@ system's block device. ::
 
 If the drive is in readonly state, bdev.ioctl(7, 0) returns `True`.
 
+The filesystem of the board has to be of FAT type for mounting  and using with standard PC
+tools. But FAT is not enforced at the board. If the board's filesystem is littlefs, the
+filesystem will still be attached to the PC and will be accesible as a drive
+(e.g. /dev/sdc usign Linux), but by default there is no file access. In that case,
+the files are locally still writable. Changing the board's filesystem to FAT can be done
+then by formatting it from the PC. Alternatively, you can erase the root sector.
+Then, the FAT filesystem will be created at the next power-up. For erasing the root sector, write::
+
+    from mimxrt import Flash
+    Flash().ioctl(6, 0)
+
+Using littlefs-fuse for Linux you can mount the board's littlefs file system to the PC.
+See: https://github.com/littlefs-project/littlefs-fuse
+The block_size if 4096, the block_count depends on the size of the filesystem. e.g.::
+
+    # mounting the lfs2 filesystem of a Teensy 4.1 board at the PC
+    mkdir mount
+    sudo ./lfs --block_size=4096 --block_count=1791 -o allow_other -o nonempty /dev/sdc mount
+    cd mount
+    ls -l
+
+In that case, the exclusive write access is NOT enforced. So be careful to only write
+to the filesystem by the PC.
 
 Transferring files
 ------------------
