circuitpython/docs/zephyr/tutorial/storage.rst

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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 `os Filesystem Mounting <https://docs.micropython.org/en/latest/library/os.html?highlight=os#filesystem-mounting>`_.
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 `os.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).
Example usage of FatFS with an SD card on the mimxrt1050_evk board::
import os
from zephyr import DiskAccess
bdev = zephyr.DiskAccess('SDHC') # create block device object using DiskAccess
os.VfsFat.mkfs(bdev) # create FAT filesystem object using the disk storage block
os.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
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 `os.AbstractBlockDev` protocol.
Example usage with the internal flash on the reel_board or the rv32m1_vega_ri5cy board::
import os
from zephyr import FlashArea
bdev = FlashArea(FlashArea.STORAGE, 4096) # create block device object using FlashArea
os.VfsLfs2.mkfs(bdev) # create Little filesystem object using the flash area block
os.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
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 ``FlashArea.STORAGE`` with the integer value 4.