QUESTION


How do I read the device serial number in MicroPython?

I want some unique* way to identify my micro:bit, how can I do this?


ANSWER


from microbit import *

display.show('S')

def get_serial_number(type=hex):
    NRF_FICR_BASE = 0x10000000
    DEVICEID_INDEX = 25 # deviceid[1]

    @micropython.asm_thumb
    def reg_read(r0):
        ldr(r0, [r0, 0])
    return type(reg_read(NRF_FICR_BASE + (DEVICEID_INDEX*4)))
    
while True:
    if button_a.was_pressed():
        display.scroll(get_serial_number())
        sleep(1000)
        display.show('S')
        
    sleep(100)
    
 


DESCRIPTION


The micro:bit has a register mapped into it's memory called the FICR (factory information configuration register) that stores information programmed in at manufacturing time. One of the items programmed in is a unique* serial number. 


The code above uses a little bit of assembly language to read this register value and display it.


MORE INFORMATION


[1] NRF51 SDK header file with register map

https://github.com/lancaster-university/nrf51-sdk/blob/85dd2e7af27edb11b056efcda34a76cf8757ef47/source/nordic_sdk/components/device/nrf51.h#L1076


* The serial is actually a 64-bit factory generated pseudo-random number etched into each processor. Only 32 bits are used here though (as that makes it consistent for all the micro:bit higher level languages to deal with), and still enables it to be unique for most practical applications. To put this into context, you'd need about 100,000 to 250,000 micro:bits in one place to expect a duplication.


ATTRIBUTION


Based on an idea from Carlos here: https://gist.github.com/microbit-carlos/d3110c69ee30ee2c92feca1397105cb0


This article was written in collaboration with 'Luke' at PyConUK 2017


Thanks to Karl Marklund for clarifying whether devices are truly unique*


REVIEWED


29/10/2017 DW