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GCoAP FileSystem

This examples set-up a CoAP server VFS. This application mimics an OBC which would hold the updates file destined to the ThingSat payload.

Note

The gcoap module in master expects IPv6 addressing. But CSP is used here which does not use or support IP. To workaround this, destination addresses for requests should be formatted as IPv6 addresses with trailing zeros. Internal the CSP sock_udp module ignores all but the first 2 bytes.

e.g.:

> csp
csp
can0       addr: 39:E5 netmask: 4 mtu: 247
           tx: 00000 rx: 00000 txe: 00000 rxe: 00000
           drop: 00000 autherr: 00000 frame: 00000
           txb: 0 (0B) rxb: 0 (0B)

The CSP address 39:E5 or 0x39E5 would become ::39e5 Ipv6 address.

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, fatfs 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 gcoap_fs example application on the native target:
make -C examples/gcoap_fs all term
[...]
main(): This is RIOT! (Version: 2018.04-devel-/examples/gcoap_fs)
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!

You can access the file system from another board that runs the gcoap_csp_cli example

> coap get ::33 2 /vfs/nvm0/
gcoap_cli: sending msg ID 32856, 16 bytes
> gcoap: response Success, code 2.05, 17 bytes
<fw/>,<cubedate/>