RIOT/examples/filesystem/README.md

File system usage example

Description

This basic example shows how to use a file system with RIOT in your embedded application.

In particular, this example shows:

• how to mount/format/unmount a file system, either with spiffs, littlefs or constfs
• how to open/read/write/close a file with and without newlib

In RIOT, most file systems use a mtd as flash interface. So to use this example one must define MTD_0. MTD_0 is a pointer to a mtd_dev_t instance.

This example uses littlefs as default file system on the whole mtd. A constfs file system is also demonstrated with two files.

All the RIOT file systems are used through the vfs interface, and on most platforms files can be accessed transparently with open/close/read/write/... functions. With newlib, fopen/fclose/fread/fwrite/... can also be used transparently.

Shell commands

The following commands are available:

• format: should be called the first time only, it will format the mtd with the configured file system
• mount: mount the file system on the configured mount point (default is /sda but it can be configured with FLASH_MOUNT_POINT define). The constfs file system is mounted automatically on /const when the application starts
• umount: unmount /sda
• cat <file>: similarly to unix cat unix command, it prints the given <file> on stdout
• tee <file> <str>: similarly to tee unix command, it writes <str> in <file>

Besides of these commands, the default vfs commands can be used, for instance:

• vfs df: shows all mountpoints and used/available file system space
• vfs ls <path>: list files

Example on native with constfs

• Build and run the filesystem example application on the native target:

make -C examples/filesystem all term
[...]
main(): This is RIOT! (Version: 2018.04-devel-/examples/filesystem)
constfs mounted successfully

• List the available files in the constfs predefined partition:

> ls /const
ls /const
/hello-world
/hello-riot
total 2 files

• Print the content of the files:

> cat /const/hello-world
cat /const/hello-world
Hello World!
> cat /const/hello-riot
cat /const/hello-riot
Hello RIOT!

Example on native with fatfs

• Unpack the provided image proviced in the pkg_fatfs test:

$ tar vxjf ../../tests/pkg_fatfs/riot_fatfs_disk.tar.bz2
riot_fatfs_disk.img

• Configure the application to use the file and the right geometry by adding these to the Makefile:

CFLAGS += -DMTD_NATIVE_FILENAME=\"riot_fatfs_disk.img\"
CFLAGS += -DMTD_PAGE_SIZE=512
CFLAGS += -DMTD_SECTOR_SIZE=512
CFLAGS += -DMTD_SECTOR_NUM=262144

• In the Makefile, comment the littlefs2 USEMODULE line, and enable the fatfs_vfs line instead.

• Build and run the filesystem example application on the native target as above.

• Mount the external file system:

> mount
mount
/sda successfully mounted

• List the available files in the FAT partition:

> ls /sda
ls /sda
TEST.TXT
total 1 files

• You can also use the writing commands now to create and modify files; run vfs for instructions.