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. This allowsto use file system to store sketch data, configuration files, or contentfor Web server.

The following diagram illustrates flash layout used in Arduinoenvironment:

|--------------|-------|---------------|--|--|--|--|--|^^^^^SketchOTAupdateFilesystemEEPROMWiFiconfig(SDK)

File system size depends on the flash chip size. Depending on the boardwhich is selected in IDE, you have the following options for flash size:

Note: to use any of file system functions in the sketch, add thefollowing include to the sketch:

#include "FS.h"

File system limitations¶

The filesystem implementation for ESP8266 had to accomodate theconstraints of the chip, among which its limited RAM.SPIFFS was selected because itis designed for small systems, but that comes at the cost of somesimplifications and limitations.

First, behind the scenes, SPIFFS does not support directories, it juststores a “flat” list of files. But contrary to traditional filesystems,the slash character'/' is allowed in filenames, so the functionsthat deal with directory listing (e.g.openDir("/website"))basically just filter the filenames and keep the ones that start withthe requested prefix (/website/). Practically speaking, that makeslittle difference though.

Second, there is a limit of 32 chars in total for filenames. One'\0' char is reserved for C string termination, so that leaves uswith 31 usable characters.

Combined, that means it is advised to keep filenames short and not usedeeply nested directories, as the full path of each file (includingdirectories,'/' characters, base name, dot and extension) has to be31 chars at a maximum. For example, the filename/website/images/bird_thumbnail.jpg is 34 chars and will cause someproblems if used, for example inexists() or in case another filestarts with the same first 31 characters.

Warning: That limit is easily reached and if ignored, problems mightgo unnoticed because no error message will appear at compilation norruntime.

For more details on the internals of SPIFFS implementation, see theSPIFFS readmefile.

Uploading files to file system¶

ESP8266FS is a tool which integrates into the Arduino IDE. It adds amenu item toTools menu for uploading the contents of sketch datadirectory into ESP8266 flash file system.

• Download the tool:https://github.com/esp8266/arduino-esp8266fs-plugin/releases/download/0.3.0/ESP8266FS-0.3.0.zip.
• In your Arduino sketchbook directory, createtools directory ifit doesn’t exist yet
• Unpack the tool intotools directory (the path will look like<home_dir>/Arduino/tools/ESP8266FS/tool/esp8266fs.jar)
• 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 nameddata and any files you want in the filesystem there
• Make sure you have selected a board, port, and closed Serial Monitor
• Select Tools > ESP8266 Sketch Data Upload. This should startuploading the files into ESP8266 flash file system. When done, IDEstatus bar will displaySPIFFSImageUploaded message.

File system object (SPIFFS)¶

SPIFFS.begin()

SPIFFS.end()

SPIFFS.format()

SPIFFS.open(path,mode)

rOpentextfileforreading.Thestreamispositionedatthebeginningofthefile.r+Openforreadingandwriting.Thestreamispositionedatthebeginningofthefile.wTruncatefiletozerolengthorcreatetextfileforwriting.Thestreamispositionedatthebeginningofthefile.w+Openforreadingandwriting.Thefileiscreatedifitdoesnotexist,otherwiseitistruncated.Thestreamispositionedatthebeginningofthefile.aOpenforappending(writingatendoffile).Thefileiscreatedifitdoesnotexist.Thestreamispositionedattheendofthefile.a+Openforreadingandappending(writingatendoffile).Thefileiscreatedifitdoesnotexist.Theinitialfilepositionforreadingisatthebeginningofthefile,butoutputisalwaysappendedtotheendofthefile.

File f = SPIFFS.open("/f.txt", "w");if (!f) {    Serial.println("file open failed");}

SPIFFS.exists(path)

SPIFFS.openDir(path)

SPIFFS.remove(path)

SPIFFS.rename(pathFrom,pathTo)

FSInfofs_info;SPIFFS.info(fs_info);

Filesystem information structure¶

structFSInfo{size_ttotalBytes;size_tusedBytes;size_tblockSize;size_tpageSize;size_tmaxOpenFiles;size_tmaxPathLength;};

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 — SPIFFSblock size -pageSize — SPIFFS logical page size -maxOpenFiles— max number of files which may be open simultaneously -maxPathLength — max file name length (including one byte for zerotermination)

Directory object (Dir)¶

The purpose ofDir object is to iterate over files inside a directory.It provides three methods:next(),fileName(), andopenFile(mode).

The following example shows how it should be used:

Dirdir=SPIFFS.openDir("/data");while(dir.next()){Serial.print(dir.fileName());Filef=dir.openFile("r");Serial.println(f.size());}

dir.next() returns true while there are files in the directory toiterate over. It must be called before callingfileName andopenFile functions.

openFile method takesmode argument which has the same meaning asforSPIFFS.open function.

File object¶

SPIFFS.open anddir.openFile functions return aFile object.This object supports all the functions ofStream, so you can usereadBytes,findUntil,parseInt,println, and all otherStream methods.

There are also some functions which are specific toFile object.

file.seek(offset,mode)

file.position()

file.size()

Stringname=file.name();

file.close()