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3. 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.

3.1. Disk Access

The zephyr.DiskAccess class can be used to access storage devices, such as SD cards. This class uses Zephyr Disk Access API 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

3.2. Flash Area

The 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 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.