Here is a solution to create an unique identifier that is based on the device's MAC address (but is not easy to guess and is not the MAC address itself):

/** Returns a hashed uint64_t */
uint64_t getHashedInt64(uint64_t u)
{
    uint64_t v = u * 3935559000370003845 + 2691343689449507681;

    v ^= v >> 21;
    v ^= v << 37;
    v ^= v >> 4;

    v *= 4768777513237032717;

    v ^= v << 20;
    v ^= v >> 41;
    v ^= v << 5;

    return v;
}

/** Return a device unique identifier based on device's mac address, eg. 6C4080B51A5D3659 */
String getUniqueId()
{
    uint64_t mac = ESP.getEfuseMac();
    uint64_t hash = getHashedInt64(mac);
    uint32_t msb = hash >> 32;
    uint32_t lsb = hash & 0xFFFFFFFF;

    char unique_id[20];
    sprintf(unique_id, "%08X%08X", msb, lsb);
    return String(unique_id);
}

Calling:
getUniqueId() returns something like 6C4080B51A5D3659

Actually, my bad, I ran the same code again on 3 different M5Paper and it is indeed working...

So yes, getMACString is returning a unique id.

`
[global_setting.cpp:70] getMACString(): MAC = 0000CC240805613C
[main.cpp:261] run(): getEfuseMac: 0805613C

[global_setting.cpp:70] getMACString(): MAC = 0000CC370805613C
[main.cpp:261] run(): getEfuseMac: 0805613C

[global_setting.cpp:70] getMACString(): MAC = 000084170905613C
[main.cpp:261] run(): getEfuseMac: 0905613C
`

Thanks

Hello,

Just started using Visual Studio Code with the PlatformIO extension to develop a simple app for m5paper starting from the online image sample.
https://github.com/m5stack/M5EPD_OnlineImage_FixUrl

If I try debugging, the code does not build:
cannot open source file "AvailabilityMacros.h" (dependency of "M5EPD.h")

Any idea where is this library?

Any help is appreciated,
Gionata