Where is data logging stored on the micro:bit V2?

[kevinjwalters]

Not something I've used but I've seen the docs for the data logging feature in MicroPython. For the micro:bit V2 I'm curious where the data is stored. Is this in flash and is it stored on the interface microcontroller or the main (target) microcontroller?

I see https://support.microbit.org/support/solutions/articles/19000129031-data-logging-faq says

Where is the data stored?

The data is stored on the micro:bit (specifically in designated space on the USB chip). If you choose to download or copy it, it may also be stored on your computer. No data is uploaded to the internet or shared with anyone, unless you choose to do this as part of your work.

That makes it sound like it's only on the interface microcontroller and not the main microcontroller?

[jonnor]

MicroBit uses a quite particular build of MicroPython. So this questions might be better addressed to the maintainers for microbit-micropython

[shariltumin]

The data gathered by the log module will be written to the "MY_DATA.HTM" file in the designated location.

You can view the log data in a browser. For example, in my case (Linux Mint, Firefox), it (URL) would be:

file:///media/sharil/MICROBIT/MY_DATA.HTM

The "MY_DATA.HTM" file contains all the HTML, CSS, and JavaScript necessary to render the logged data properly. You can use the command cat MY_DATA.HTM in a terminal to see what it looks like.

Try this script:

from microbit import run_every, sleep, temperature
import log

@run_every(s=10)
def log_temp():
    log.add(temp=temperature())

while True:
    sleep(100) # prevent script ending

I use mpremote to access the REPL.
+e (copy(<ctrl+shift>+c) and paste(<ctrl+shift>+v)) +d
Let it run for a while, then press +c(KeyboardInterrupt).

[kevinjwalters]

@shariltumin I intended my question to be about where the data resides in terms of which of the two microcontrollers holds the data. And if it's in RAM or flash memory.

[shariltumin]

I do not understand your question: "....where the data resides in terms of which of the two microcontrollers holds the data. And if it's in RAM or flash memory."

There are no two microcontrollers, it is the micro:bit and the PC to which you connect the micro:bit. In the MicroPython version on the micro:bit.V2 the log is saved on a special location in the flash memory. Any PC connected to the micro:bit can copy the log from file:///<mount_point>/MICROBIT/MY_DATA.HTM using a browser. On Windows, you can just click on the "MY_DATA.HTM" (maybe, I work on a Linux PC)

[kevinjwalters]

The Hardware block diagram shows the two microcontrollers on https://tech.microbit.org/hardware/#hardware-block-diagram - the application (or target) MCU is on the left, the interface MCU is on the right.

[shariltumin]

Now I see what you meant. There are two, as you said. The log data is stored in the flash memory of the interface MCU. The interface MCU provides USB serial and USB mass storage. However, it is not possible to access the data in the interface MCU flash from a script that runs on the main MCU.

You can write and read files in the main MCU flash memory using the open(), write(), close(), open(), read(), and close() functions from a MicroPython script. However, my custom firmware seems to be broken when performing these file operations. You can use the os module to list and remove files stored in the main MCU flash.

[shariltumin]

It seems that the file operations must be performed in binary mode.

>>> f = open('test.txt', 'wb')
>>> f.write(b'Hello World!')
12
>>> f.close()
>>> f = open('test.txt', 'rb')
>>> w = f.read(100)
>>> w.decode()
'Hello World!'
>>> os.listdir()
['test.txt']
>>> os.size('test.txt')
12
>>> os.remove('test.txt')
>>> os.listdir()
[]