.. _usb_mass:

USB Mass Storage Sample Application
###################################

Overview
********

This sample app demonstrates use of a USB Mass Storage driver by the Zephyr
project.  This very simple driver enumerates a board with either RAM or FLASH
into an USB disk.  This sample can be found under
:zephyr_file:`samples/subsys/usb/mass` in the Zephyr project tree.

Requirements
************

This project requires a USB device driver, and either 16KiB of RAM or a FLASH
device.

Building and Running
********************

This sample can be built for multiple boards, some generic and some
customized through configurations found in
:zephyr_file:`samples/subsys/usb/mass/boards` in the Zephyr project
tree.

Generic Example
===============

The selection between a RAM-based or a FLASH-based disk can be selected
using the ``overlay-ram-disk.conf`` or the ``overlay-flash-disk.conf``
overlays.  In this example we will build the sample with a RAM-based
disk:

.. zephyr-app-commands::
   :zephyr-app: samples/subsys/usb/mass
   :board: reel_board
   :gen-args: -DOVERLAY_CONFIG="overlay-ram-disk.conf"
   :goals: build
   :compact:

After you have built and flashed the sample app image to your board, plug the
board into a host device, for example, a PC running Linux.
The board will be detected as shown by the Linux journalctl command:

.. code-block:: console

    $ journalctl -k -n 17
    usb 2-2.4: new full-speed USB device number 29 using xhci_hcd
    usb 2-2.4: New USB device found, idVendor=2fe3, idProduct=0100, bcdDevice= 0.11
    usb 2-2.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
    usb 2-2.4: Product: Zephyr MSC sample
    usb 2-2.4: Manufacturer: ZEPHYR
    usb 2-2.4: SerialNumber: 0.01
    usb-storage 2-2.4:1.0: USB Mass Storage device detected
    scsi host3: usb-storage 2-2.4:1.0
    scsi 3:0:0:0: Direct-Access     ZEPHYR   ZEPHYR USB DISK  0.01 PQ: 0 ANSI: 0 CCS
    sd 3:0:0:0: Attached scsi generic sg1 type 0
    sd 3:0:0:0: [sdb] 32 512-byte logical blocks: (16.4 kB/16.0 KiB)
    sd 3:0:0:0: [sdb] Write Protect is off
    sd 3:0:0:0: [sdb] Mode Sense: 03 00 00 00
    sd 3:0:0:0: [sdb] No Caching mode page found
    sd 3:0:0:0: [sdb] Assuming drive cache: write through
     sdb:
    sd 3:0:0:0: [sdb] Attached SCSI removable disk

The disk contains a simple ``README.TXT`` file with the following content:

.. code-block:: console

    This is a  RAM Disk based  USB Mass Storage demo for Zephyr.

Files can be added or removed like with a simple USB disk, of course within
the 16KiB limit.

nrf52840dk_nrf52840 Example
===========================

This board configures to use the external 64 MiBi QSPI flash chip with a
64 KiBy `littlefs`_ partition compatible with the one produced by the
:ref:`littlefs-sample`.  While a FAT-based file system can be mounted by
many systems automatically, mounting the littlefs file system on a Linux
or FreeBSD system can be accomplished using the `littlefs-FUSE`_ utility.

.. zephyr-app-commands::
   :zephyr-app: samples/subsys/usb/mass
   :board: nrf52840dk_nrf52840
   :goals: build
   :compact:

After you have built and flashed the sample app image to your board,
connect the board's two USB connectors (debug and nRF USB) to a host
running a littlefs-FUSE-capable operating system.  The output to the
console will look something like this (file system contents will be
different):

.. code-block:: none

    *** Booting Zephyr OS build zephyr-v2.2.0-1966-g7815942d5fc5  ***
    Area 4 at 0x0 on MX25R64 for 65536 bytes
    [00:00:00.005,310] <inf> main: The device is put in USB mass storage mode.

    [00:00:00.009,002] <inf> littlefs: LittleFS version 2.2, disk version 2.0
    [00:00:00.009,063] <inf> littlefs: FS at MX25R64:0x0 is 16 0x1000-byte blocks with 512 cye
    [00:00:00.009,063] <inf> littlefs: sizes: rd 16 ; pr 16 ; ca 64 ; la 32
    [00:00:00.011,718] <inf> littlefs: /lfs mounted
    Mount /lfs: 0
    /lfs: bsize = 16 ; frsize = 4096 ; blocks = 16 ; bfree = 13
    /lfs opendir: 0
      F 8 hi
      F 128 linux
      F 5 newfile
    End of files

Determine the local device name from the system log, e.g.:

.. code-block:: none

    Apr 25 08:10:25 tirzah kernel: [570310.921039] scsi 17:0:0:0: Direct-Access     ZEPHYR   ZEPHYR USB DISK  0.01 PQ: 0 ANSI: 0 CCS
    Apr 25 08:10:25 tirzah kernel: [570310.921550] sd 17:0:0:0: Attached scsi generic sg4 type 0
    Apr 25 08:10:25 tirzah kernel: [570310.922277] sd 17:0:0:0: [sdd] 128 512-byte logical blocks: (65.5 kB/64.0 KiB)
    Apr 25 08:10:25 tirzah kernel: [570310.922696] sd 17:0:0:0: [sdd] Write Protect is off

This shows that the block device associated with the USB drive is
``/dev/sdd``:

.. code-block:: shell

    tirzah[447]$ ll /dev/sdd
    brw-rw---- 1 root disk 8, 48 Apr 25 08:10 /dev/sdd

This can be mounted as a file system with the following commands:

.. code-block:: shell

   sudo chmod a+rw /dev/sdd   # required to allow user access
   mkdir /tmp/lfs
   lfs \
          --read_size=16 \
          --prog_size=16 \
          --block_size=4096 \
          --block_count=16 \
          --cache_size=64 \
          --lookahead_size=32 \
          /dev/sdd /tmp/lfs

which produces this output:

.. code-block:: none

    tirzah[467]$ ls -l /tmp/lfs
    total 0
    -rwxrwxrwx 0 root root   8 Dec 31  1969 hi
    -rwxrwxrwx 0 root root 128 Dec 31  1969 linux
    -rwxrwxrwx 0 root root   5 Dec 31  1969 newfile

``lfs`` is a mount command and you should take care to unmount the
device before removing the USB drive:

.. code-block:: shell

   umount /tmp/lfs

littlefs parameter selection
----------------------------

Be aware that the parameters passed to :command:`lfs` in the example
above **must** exactly match the corresponding parameters used to
initialize the file system.  The required parameters can be observed
from the Zephyr mount log messages:

.. code-block:: none

    [00:00:00.009,002] <inf> littlefs: LittleFS version 2.2, disk version 2.0
    [00:00:00.009,063] <inf> littlefs: FS at MX25R64:0x0 is 16 0x1000-byte blocks with 512 cye
    [00:00:00.009,063] <inf> littlefs: sizes: rd 16 ; pr 16 ; ca 64 ; la 32

* ``--read_size`` corresponds to the ``rd`` size and is 16;
* ``--prog_size`` corresponds to the ``pr`` size and is 16;
* ``--block_size`` comes from ``0x1000-byte blocks`` and is 4096 (0x1000);
* ``--block_count`` comes from ``16 0x1000-byte blocks`` and is 16;
* ``--cache_size`` comes from the ``ca`` size and is 64;
* ``--lookahead_size`` comes from the ``la`` size and is 32

If any of the parameters are inconsistent between the Zephyr and Linux
specification the file system will not mount correctly.

.. _littlefs: https://github.com/ARMmbed/littlefs
.. _littlefs-FUSE: https://github.com/ARMmbed/littlefs-fuse