NanoBLEFlashPrefs

Substitute for missing EEPROM storage on Arduino Nano 33 BLE and 33 BLE Sense (not for Nano 33 IoT or other Nano boards).

Info

Arduino Nano 33 BLE and 33 BLE Sense do not have an EEPROM where you can store any parameters permanently. This library allows to store parameters and preferences between program restarts and even reflashing.

The Arduino boards mentioned above use a nRF52840 microcontroller from Nordic Semiconductor. This chip features a very simple file system for flash storage. It is used here to easily store and retrieve an arbitrary struct of preferences of your sketch.

Please note: Starting with version 1.1 of the library, all functions are synchronous. Therefore you should remove waiting loops with calls to operationCompleted() in your existing code.

Installation

• Search for NanoBLEFlashPrefs in the library manager of your Arduino IDE and install it.

Alternatively:

• Select Download ZIP from the GitHub Code button. Unzip the archive if it isn't already. You will end up with a folder NanoBLEFlashPrefs-master in your download folder.

• Rename that folder to NanoBLEFlashPrefs.

• Move it to Arduino/libraries in your documents folder.

• Restart Arduino IDE.

The library has been tested with Arduino Nano 33 BLE and version 2.4.1 of this board's SDK. Make sure you have at least this version of Arduino Mbed OS Nano Boards installed.

Usage

See the enclosed NanoBLEFlashPrefsTest example. You can store any preferences you like in a struct like this:

// Preferences structure. Arbitrary, but must not exeed 1019 words (4076 byte)
typedef struct flashStruct {
	char someString[64];
	bool aSetting;
	int  someNumber;
	float anotherNumber;
} flashPrefs;

This is how you read and write preferences:

NanoBLEFlashPrefs myFlashPrefs;
flashPrefs prefs;

int rc = myFlashPrefs.readPrefs(&prefs, sizeof(prefs));

// Prepare preference record for writing
strcpy(prefs.someString, "NanoBLEFlashPrefs Test");
prefs.aSetting = true;
prefs.someNumber = 42;
prefs.anotherNumber = 3.14;
// Write it to flash memory
myFlashPrefs.writePrefs(&prefs, sizeof(prefs));

In order to understand the return values of the functions, use errorString() like this:

int rc = myFlashPrefs.readPrefs(&prefs, sizeof(prefs));
Serial.println(myFlashPrefs.errorString(rc));

If you want to learn more about the status of your Nano 33 BLE flash file system, use statusString() like this:

Serial.println(myFlashPrefs.statusString());

For interpretation of this information look at the nRF5 SDK website.

Garbage collection is also supported. deletePrefs() actually only invalidates a preference record, so flash usage gradually increases. Use garbageCollection() to clear the file system from all invalid (deleted) preference records. Please see the NanoBLEFlashPrefsUtils sample code for more information.

TODO

Library

• Test on Arduino Nano 33 BLE Sense

Documentation

• Expand.

Credits

See nRF5 SDK by Nordic Semiconductor for sample code and additional information.