Portenta Flash Storage

This library allows you to easily use the flash storage of the Portenta H7. It is based on the flash optimized key value store example from Arduino, but provides a nice wrapper around it.

Guide

Defining your data structure

In the library there is a header called FlashStruct.h, which contains a default struct that looks like this:

struct FlashKeyValueStruct
{
	bool booleanValue;
	double doubleValue;
};

More than likely this is not the format of data you want to store, so first modify the struct to match your data structure. In most PlatformIO installations this file can be found in the following directory inside your project:

.pio/libdeps/portenta_h7_m7/portenta-flashstorage/src/FlashStruct.h

You do not need to change any other part of the library to make your struct compatible. The library will automatically read the in-memory size of your struct and use it accordingly. Do not change the name of the struct.

This guide will use the default struct provided, so make sure to modify your references to the struct when they come up.

Include the library

Include the library in your main.cpp or other files using:

#include "FlashKeyValue.h"

Initializing the flash

You must initialize the flash before using it, otherwise reading/writing will return error codes. To do this, call the FlashKeyValue::init() function like this:

int result = FlashKeyValue::init();
// optional - test for successful initialization
Serial.println(result == 1 ? "OK" : "Failed");
if (result != 1)
	while (true); // Stop the firmware if an error occurs

Reading from flash

To read from flash, you must first create a variable of your struct type. Then call the FlashKeyValue::get function with a pointer to your variable like this:

// Will store the value currently in flash
FlashKeyValueStruct value;

int result = FlashKeyValue::get(&previousValue);

You should always handle the following conditions of result, since they determine whether or not value has any actual data in it. Here are the values you should test for:

Result Code	Meaning
MBED_SUCCESS	The value was successfully read from flash
MBED_ERROR_ITEM_NOT_FOUND	The key was not found in flash, but flash is working properly
MBED_ERROR_NOT_READY	Flash was not initialized
MBED_ERROR_READ_FAILED	Flash is not working properly
MBED_ERROR_INVALID_ARGUMENT	An internal error occurred
MBED_ERROR_INVALID_DATA_DETECTED	Your data does not match the previous data stored in flash. Try using FlashKeyValue::erase to reset flash

Here's a sample of how to appropriately handle these conditions:

if (result == MBED_SUCCESS) {
	// We can now read our data, just as if it was a normal variable
	Serial.println("Values from flash");
	Serial.print("\Boolean value: ");
	Serial.println(previousValue.booleanValue);
	Serial.print("\Double value: ");
	Serial.println(previousValue.doubleValue);
} else if (result == MBED_ERROR_ITEM_NOT_FOUND) {
	Serial.println("No data was found.");
	// You can initialize your data here if you want
	previousValue = { false, 0.0 };
} else {
	// Another error occurred, handle it here
	Serial.print("Error reading from key-value store with code: ");
	Serial.println(result);
	while (true);
}

Storing to flash

To store to flash, you must first create a variable of your struct type. Then call the FlashKeyValue::set function with a pointer to your variable like this:

FlashKeyValueStruct newValue { 
	true, 0.2
};  

int result = FlashKeyValue::set(newValue);

To make sure your data was successfully stored in flash, you should test for the following conditions of result:

Result Code	Meaning
MBED_SUCCESS	The value was successfully written to flash
Other	An error occurred on the mbed level. Make sure flash is properly initialized

Here's a sample of how to appropriately handle these conditions:

if (result == MBED_SUCCESS) {
	Serial.println("Value set");
} else {
	Serial.println("Error while saving to key-value store");
	while (true);
}

Erasing flash contents

To erase the contents of flash, call the FlashKeyValue::erase function like this:

FlashKeyValue::erase();

Examples

You can see a complete working example in the examples/basic-usage directory.

API

bool init();

Initializes the flash storage. This must be called before any other functions are called. Returns true if successful, otherwise returns false.

int get(FlashKeyValueStruct* value);

Reads the value from flash into the provided struct using the default key. Returns an mbed error code.

int get(const char* key, FlashKeyValueStruct* value);

Reads the value from flash into the provided struct using the provided key. Returns an mbed error code.

int set(FlashKeyValueStruct value);

Writes the provided struct to flash using the default key. Returns an mbed error code.

int set(const char* key, FlashKeyValueStruct value);

Writes the provided struct to flash using the provided key. Returns an mbed error code.

int erase();

Erases the contents of flash. Returns 0 if successful.