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.. _storage_zephyr:
Filesystems and Storage
=======================
Storage modules support virtual filesystem with FAT and littlefs formats, backed by either
Zephyr DiskAccess or FlashArea (flash map) APIs depending on which the board supports.
See `vfs Filesystem Mounting <https://docs.micropython.org/en/latest/library/vfs.html?highlight=vfs#filesystem-mounting>`_.
Automatic Filesystem Mounting
------------------------------
MicroPython on Zephyr automatically attempts to mount available storage at startup:
1. **Flash storage** (if available): Automatically mounted at ``/flash`` using the
littlefs2 filesystem. If the filesystem doesn't exist, it will be created
automatically.
2. **Disk storage** (such as SD cards): Automatically detected and mounted at
``/<disk_name>`` (e.g., ``/sd`` for SD cards).
3. **Working directory**: The working directory is set to the mounted disk if
available, otherwise to ``/flash`` if flash storage is available.
4. **Module search path**: The ``sys.path`` is automatically updated to include
``/<disk>/lib`` for each mounted disk and ``/flash/lib`` for flash storage.
This automatic mounting is performed by the ``_boot.py`` module at startup. For most
use cases, you don't need to manually mount filesystems.
Disk Access
-----------
The :ref:`zephyr.DiskAccess <zephyr.DiskAccess>` class can be used to access storage devices, such as SD cards.
This class uses `Zephyr Disk Access API <https://docs.zephyrproject.org/latest/reference/storage/disk/access.html>`_ and
implements the `vfs.AbstractBlockDev` protocol.
For use with SD card controllers, SD cards must be present at boot & not removed; they will
be auto detected and initialized by filesystem at boot. Use the disk driver interface and a
file system to access SD cards via disk access (see below).
The available disk names can be accessed via the ``DiskAccess.disks`` attribute, which contains
a tuple of available disk names (e.g., ``('SDHC',)`` or ``('SD',)``).
Example usage of FatFS with an SD card on the mimxrt1050_evk board::
import vfs
from zephyr import DiskAccess
# List available disks
print(DiskAccess.disks) # prints available disk names, e.g., ('SDHC',)
bdev = DiskAccess('SDHC') # create block device object using DiskAccess
vfs.VfsFat.mkfs(bdev) # create FAT filesystem object using the disk storage block
vfs.mount(bdev, '/sd') # mount the filesystem at the SD card subdirectory
with open('/sd/hello.txt','w') as f: # open a new file in the directory
f.write('Hello world') # write to the file
print(open('/sd/hello.txt').read()) # print contents of the file
Note: In most cases, disks are automatically mounted at startup and manual mounting is not necessary.
Flash Area
----------
The :ref:`zephyr.FlashArea <zephyr.FlashArea>` class can be used to implement a low-level storage system or
customize filesystem configurations. To store persistent data on the device, using a higher-level filesystem
API is recommended (see below).
This class uses `Zephyr Flash map API <https://docs.zephyrproject.org/latest/reference/storage/flash_map/flash_map.html#>`_ and
implements the `vfs.AbstractBlockDev` protocol.
The available flash area names can be accessed via the ``FlashArea.areas`` dictionary, which maps partition
labels to their IDs (e.g., ``{'storage': 1, 'scratch': 4}``).
Example usage with the internal flash on the reel_board or the rv32m1_vega_ri5cy board::
import vfs
from zephyr import FlashArea
# List available flash areas
print(FlashArea.areas) # prints available areas, e.g., {'storage': 1, 'scratch': 4}
bdev = FlashArea(FlashArea.areas['storage'], 4096) # create block device object using FlashArea
vfs.VfsLfs2.mkfs(bdev) # create Little filesystem object using the flash area block
vfs.mount(bdev, '/flash') # mount the filesystem at the flash storage subdirectory
with open('/flash/hello.txt','w') as f: # open a new file in the directory
f.write('Hello world') # write to the file
print(open('/flash/hello.txt').read()) # print contents of the file
Note: In most cases, the flash storage partition is automatically mounted at ``/flash`` at startup with
automatic filesystem creation if needed, so manual mounting is not necessary.
For boards such as the frdm_k64f in which the MicroPython application spills into the default flash storage
partition, use the scratch partition by replacing ``'storage'`` with ``'scratch'``.
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