USB Mass Storage Sample Application¶
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 samples/subsys/usb/mass in the Zephyr project tree.
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 samples/subsys/usb/mass/boards in the Zephyr project tree.
The selection between a RAM-based or a FLASH-based disk can be selected
overlay-ram-disk.conf or the
overlays. In this example we will build the sample with a RAM-based
west build -b reel_board samples/subsys/usb/mass -- -DOVERLAY_CONFIG="overlay-ram-disk.conf"
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:
$ 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=0008, bcdDevice= 2.03 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: 86FE679A598AC47A 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:
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.
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 littlefs File System Sample Application. 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.
west build -b nrf52840dk_nrf52840 samples/subsys/usb/mass
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):
*** 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.:
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
tirzah$ 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:
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:
tirzah$ 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:
littlefs parameter selection¶
Be aware that the parameters passed to 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:
[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_sizecorresponds to the
rdsize and is 16;
--prog_sizecorresponds to the
prsize and is 16;
0x1000-byte blocksand is 4096 (0x1000);
16 0x1000-byte blocksand is 16;
--cache_sizecomes from the
casize and is 64;
--lookahead_sizecomes from the
lasize and is 32
If any of the parameters are inconsistent between the Zephyr and Linux specification the file system will not mount correctly.