File Systems
The Arduino-Pico core supports using some of the onboard flash as a file system, useful for storing configuration data, output strings, logging, and more. It also supports using SD cards as another (FAT32) filesystem, with an API that’s compatible with the onboard flash file system.
Flash Layout
Even though file system is stored on the same flash chip as the program, programming new sketch will not modify file system contents (or EEPROM data).
The following diagram shows the flash layout used in Arduino-Pico:
|---------------------|-------------|----|
^ ^ ^
Sketch File system EEPROM
The file system size is configurable via the IDE menus, rom 64k up to 15MB (assuming you have an RP2040 boad with that much flash)
Note: to use any of file system functions in the sketch, add the following include to the sketch:
#include "LittleFS.h" // LittleFS is declared
// #include <SDFS.h>
// #include <SD.h>
Compatible Filesystem APIs
LittleFS is an onboard filesystem that sets asidesome program flash for use as a filesystem without requiring any external hardware.
SDFS is a filesystem for SD cards, based on [SdFat 2.0](https://github.com/earlephilhower/ESP8266SdFat). It supports FAT16 and FAT32 formatted cards, and requires an external SD card reader.
SD is the Arduino supported, somewhat old and limited SD card filesystem. It is recommended to use SDFS for new applications instead of SD.
All three of these filesystems can open and manipulate File
and Dir
objects with the same code because the implement a common end-user
filesystem API.
LittleFS File System Limitations
The LittleFS implementation for the RP2040 supports filenames of up
to 31 characters + terminating zero (i.e. char filename[32]
), and
as many subdirectories as space permits.
Filenames are assumed to be in the root directory if no initial “/” is present.
Opening files in subdirectories requires specifying the complete path to
the file (i.e. LittleFS.open("/sub/dir/file.txt", "r");
). Subdirectories
are automatically created when you attempt to create a file in a
subdirectory, and when the last file in a subdirectory is removed the
subdirectory itself is automatically deleted.
Uploading Files to the LittleFS File System
PicoLittleFS is a tool which integrates into the Arduino IDE. It adds a menu item to Tools menu for uploading the contents of sketch data directory into a new LittleFS flash file system.
Download the tool: https://github.com/earlephilhower/arduino-pico-littlefs-plugin/releases
In your Arduino sketchbook directory, create
tools
directory if it doesn’t exist yet.Unpack the tool into
tools
directory (the path will look like<home_dir>/Arduino/tools/PicoLittleFS/tool/picolittlefs.jar
) If upgrading, overwrite the existing JAR file with the newer version.Restart Arduino IDE.
Open a sketch (or create a new one and save it).
Go to sketch directory (choose Sketch > Show Sketch Folder).
Create a directory named
data
and any files you want in the file system there.Make sure you have selected a board, port, and closed Serial Monitor.
Double check theSerial Monitor is closed. Uploads will fail if the Serial Monitor has control of the serial port.
Select
Tools > Pico LittleFS Data Upload
. This should start uploading the files into the flash file system.
SD Library Information
The included SD
library is the Arduino standard one. Please refer to
the [Arduino SD reference](https://www.arduino.cc/en/reference/SD) for
more information.
Using Second SPI port for SD
The SD
library begin()
has been modified to allow you to use the
second SPI port, SPI1
. Just use the following call in place of
SD.begin(cspin)
SD.begin(cspin, SPI1);
File system object (LittleFS/SD/SDFS)
setConfig
LittleFSConfig cfg;
cfg.setAutoFormat(false);
LittleFS.setConfig(cfg);
SDFSConfig c2;
c2.setCSPin(12);
SDFS.setConfig(c2);
This method allows you to configure the parameters of a filesystem
before mounting. All filesystems have their own *Config
(i.e.
SDFSConfig
or LittleFSConfig
with their custom set of options.
All filesystems allow explicitly enabling/disabling formatting when
mounts fail. If you do not call this setConfig
method before
perforing begin()
, you will get the filesystem’s default
behavior and configuration. By default, SPIFFS will autoformat the
filesystem if it cannot mount it, while SDFS will not.
begin
SDFS.begin()
or LittleFS.begin()
This method mounts file system. It must be called before any other FS APIs are used. Returns true if file system was mounted successfully, false otherwise. With no options it will format SPIFFS if it is unable to mount it on the first try.
Note that LittleFS will automatically format the filesystem
if one is not detected. This is configurable via setConfig
end
SDFS.end()
or LittleFS.end()
This method unmounts the file system.
format
SDFS.format()
or LittleFS.format()
Formats the file system. May be called either before or after calling
begin
. Returns true if formatting was successful.
open
SDFS.open(path, mode)
or LittleFS.open(path, mode)
Opens a file. path
should be an absolute path starting with a slash
(e.g. /dir/filename.txt
). mode
is a string specifying access
mode. It can be one of “r”, “w”, “a”, “r+”, “w+”, “a+”. Meaning of these
modes is the same as for fopen
C function.
r Open text file for reading. The stream is positioned at the
beginning of the file.
r+ Open for reading and writing. The stream is positioned at the
beginning of the file.
w Truncate file to zero length or create text file for writing.
The stream is positioned at the beginning of the file.
w+ Open for reading and writing. The file is created if it does
not exist, otherwise it is truncated. The stream is
positioned at the beginning of the file.
a Open for appending (writing at end of file). The file is
created if it does not exist. The stream is positioned at the
end of the file.
a+ Open for reading and appending (writing at end of file). The
file is created if it does not exist. The initial file
position for reading is at the beginning of the file, but
output is always appended to the end of the file.
Returns File object. To check whether the file was opened successfully, use the boolean operator.
File f = LittleFS.open("/f.txt", "w");
if (!f) {
Serial.println("file open failed");
}
exists
SDFS.exists(path)
or LittleFS.exists(path)
Returns true if a file with given path exists, false otherwise.
mkdir
SDFS.mkdir(path)
or LittleFS.mkdir(path)
Returns true if the directory creation succeeded, false otherwise.
rmdir
SDFS.rmdir(path)
or LittleFS.rmdir(path)
Returns true if the directory was successfully removed, false otherwise.
openDir
SDFS.openDir(path)
or LittleFS.openDir(path)
Opens a directory given its absolute path. Returns a Dir object. Please note the previous discussion on the difference in behavior between LittleFS and SPIFFS for this call.
remove
SDFS.remove(path)
or LittleFS.remove(path)
Deletes the file given its absolute path. Returns true if file was deleted successfully.
rename
SDFS.rename(pathFrom, pathTo)
or LittleFS.rename(pathFrom, pathTo)
Renames file from pathFrom
to pathTo
. Paths must be absolute.
Returns true if file was renamed successfully.
info DEPRECATED
FSInfo fs_info;
or LittleFS.info(fs_info);
Fills FSInfo structure with
information about the file system. Returns true
if successful,
false
otherwise. Because this cannot report information about
filesystemd greater than 4MB, don’t use it in new code. Use info64
instead which uses 64-bit fields for filesystem sizes.
Filesystem information structure
struct FSInfo {
size_t totalBytes;
size_t usedBytes;
size_t blockSize;
size_t pageSize;
size_t maxOpenFiles;
size_t maxPathLength;
};
This is the structure which may be filled using FS::info method. -
totalBytes
— total size of useful data on the file system -
usedBytes
— number of bytes used by files - blockSize
— filesystem
block size - pageSize
— filesystem logical page size - maxOpenFiles
— max number of files which may be open simultaneously -
maxPathLength
— max file name length (including one byte for zero
termination)
info64
FSInfo64 fsinfo;
SDFS.info64(fsinfo);
or LittleFS.info64(fsinfo);
Performs the same operation as info
but allows for reporting greater than
4GB for filesystem size/used/etc. Should be used with the SD and SDFS
filesystems since most SD cards today are greater than 4GB in size.
setTimeCallback(time_t (*cb)(void))
time_t myTimeCallback() {
return 1455451200; // UNIX timestamp
}
void setup () {
LittleFS.setTimeCallback(myTimeCallback);
...
// Any files will now be made with Pris' incept date
}
The SD, SDFS, and LittleFS filesystems support a file timestamp, updated when the file is
opened for writing. By default, the Pico will use the internal time returned from
time(NULL)
(i.e. local time, not UTC, to conform to the existing FAT filesystem), but this
can be overridden to GMT or any other standard you’d like by using setTimeCallback()
.
If your app sets the system time using NTP before file operations, then
you should not need to use this function. However, if you need to set a specific time
for a file, or the system clock isn’t correct and you need to read the time from an external
RTC or use a fixed time, this call allows you do to so.
In general use, with a functioning time()
call, user applications should not need
to use this function.
Directory object (Dir)
The purpose of Dir object is to iterate over files inside a directory. It provides multiple access methods.
The following example shows how it should be used:
Dir dir = LittleFS.openDir("/data");
// or Dir dir = LittleFS.openDir("/data");
while (dir.next()) {
Serial.print(dir.fileName());
if(dir.fileSize()) {
File f = dir.openFile("r");
Serial.println(f.size());
}
}
next
Returns true while there are files in the directory to
iterate over. It must be called before calling fileName()
, fileSize()
,
and openFile()
functions.
fileName
Returns the name of the current file pointed to by the internal iterator.
fileSize
Returns the size of the current file pointed to by the internal iterator.
fileTime
Returns the time_t write time of the current file pointed to by the internal iterator.
fileCreationTime
Returns the time_t creation time of the current file pointed to by the internal iterator.
isFile
Returns true if the current file pointed to by the internal iterator is a File.
isDirectory
Returns true if the current file pointed to by the internal iterator is a Directory.
openFile
This method takes mode argument which has the same meaning as
for SDFS/LittleFS.open()
function.
rewind
Resets the internal pointer to the start of the directory.
setTimeCallback(time_t (*cb)(void))
Sets the time callback for any files accessed from this Dir object via openNextFile.
Note that the SD and SDFS filesystems only support a filesystem-wide callback and
calls to Dir::setTimeCallback
may produce unexpected behavior.
File object
SDFS/LittleFS.open()
and dir.openFile()
functions return a File object.
This object supports all the functions of Stream, so you can use
readBytes
, findUntil
, parseInt
, println
, and all other
Stream methods.
There are also some functions which are specific to File object.
seek
file.seek(offset, mode)
This function behaves like fseek
C function. Depending on the value
of mode
, it moves current position in a file as follows:
if
mode
isSeekSet
, position is set tooffset
bytes from the beginning.if
mode
isSeekCur
, current position is moved byoffset
bytes.if
mode
isSeekEnd
, position is set tooffset
bytes from the end of the file.
Returns true if position was set successfully.
position
file.position()
Returns the current position inside the file, in bytes.
size
file.size()
Returns file size, in bytes.
name
String name = file.name();
Returns short (no-path) file name, as const char*
. Convert it to String for
storage.
fullName
// Filesystem:
// testdir/
// file1
Dir d = LittleFS.openDir("testdir/");
File f = d.openFile("r");
// f.name() == "file1", f.fullName() == "testdir/file1"
Returns the full path file name as a const char*
.
getLastWrite
Returns the file last write time, and only valid for files opened in read-only mode. If a file is opened for writing, the returned time may be indeterminate.
getCreationTime
Returns the file creation time, if available.
isFile
bool amIAFile = file.isFile();
Returns true if this File points to a real file.
isDirectory
bool amIADir = file.isDir();
Returns true if this File points to a directory (used for emulation
of the SD.* interfaces with the openNextFile
method).
close
file.close()
Close the file. No other operations should be performed on File object
after close
function was called.
openNextFile (compatibiity method, not recommended for new code)
File root = LittleFS.open("/");
File file1 = root.openNextFile();
File file2 = root.openNextFile();
Opens the next file in the directory pointed to by the File. Only valid
when File.isDirectory() == true
.
rewindDirectory (compatibiity method, not recommended for new code)
File root = LittleFS.open("/");
File file1 = root.openNextFile();
file1.close();
root.rewindDirectory();
file1 = root.openNextFile(); // Opens first file in dir again
Resets the openNextFile
pointer to the top of the directory. Only
valid when File.isDirectory() == true
.
setTimeCallback(time_t (*cb)(void))
Sets the time callback for this specific file. Note that the SD and
SDFS filesystems only support a filesystem-wide callback and calls to
Dir::setTimeCallback
may produce unexpected behavior.