uBit.storage

MicroBitStorage provides a simple way to store data on the micro:bit that persists through power cycles. It currently takes the form of a key value store which contains a number of key value pairs.

If a user wanted to determine if a micro:bit has just been flashed over USB they could simply write the following:

#include "MicroBit.h"

MicroBit    uBit;

int main()
{
    uBit.init();

    KeyValuePair* firstTime = uBit.storage.get("boot");

    int stored;

    if(firstTime == NULL)
    {
        //this is the first boot after a flash. Store a value!
        stored = 1;
        uBit.storage.put("boot", (uint8_t *)&stored, sizeof(int));
        uBit.display.scroll("Stored!");
    }
    else
    {
        //this is not the first boot, scroll our stored value.
        memcpy(&stored, firstTime->value, sizeof(int));
        delete firstTime;
        uBit.display.scroll(stored);
    }
}

What is flash memory?

The micro:bit has 256 kB flash memory and 16 kB random access memory (RAM). Flash memory is non-volatile, which essentially means that data is not forgotten when the device is powered off, this is the technology that many USB sticks use.

The alternative, Random Access Memory (also known as volatile memory), cannot be persisted through power cycling the device as its operation relies upon maintaining a constant supply of power.

Therefore, MicroBitStorage utilises the non-volatile nature of flash memory, to store its data. This class is utilised by the [compass](compass.md), [accelerometer](compass.md) and [bleManager](blemanager.md) to improve the user experience by persisting calibration and bonding data.

Operations

You can put(), get() and remove() key value pairs from the store.

Key Value pairs have a fixed length key of 16 bytes, and a fixed length value of 32 bytes. This class only populates a single block (1024 bytes) in its current state, which means that 21 Key Value pairs can be stored.