development board is shown as external storage device when connected in windows

Question

so when I connect my development board (NUCLEO-f446re) to my laptop, everything is working normally, but there is only one thing that confuses me, see the next picture

windows recognize my development board as external storage device with 1.52 MB size (partition named NODE_F446RE(E:) ) when I open it, the next image show what I see

there is only 2 files there, the.HTM file takes me to this link and the.TXT file has the follow content:

Version: V2J40M27

Build: May 5 2022 13:16:48

so I don't understand what does this mean?, like what does 1.5MB storage represent in my MCU even though, the flash size of my MCU is only 512 KB which is way less than the shown storage, also what happens if I put any.exe file in that partition?

Answer 1

From the web page you link (emphasis by me):

USB re-enumeration capability: three different interfaces supported on USB

• Virtual Com port
• Mass storage (USB Disk drive) for drag'n'drop programming
• Debug port

Your board offers the option to program your application. Simply drap and drop the bin (binary) file of the application into this drive.

It is "just" a virtual drive, the software behind it does the flashing for you, if it receives a binary file.

Why the size of the drive is bigger than the available flash memory, is not clear. Perhaps to allow for necessary overhead to mimic a file system, and to have room for the files you see.

If you copy an exe file in it, I'd expect some kind of error message. Or that the file will not be stored. Experiment!

Answer 2

This functionality is perhaps not well documented, but is part of the "Mbed Enabled" functionality. It is a feature of the Mbed bootloader, to allow "drag'n'drop programming" via a "fake" mass storage device in order to avoid the need for special programming tools or protocols.

You can write to the device, but the "file" will not appear in the filesystem, rather the content will be used to program the on-chip flash memory.

The files on the fake drive are read-only - mbed.htm will open in a browser and take you to the Mbed sign-up/login where you can start developing using Mbed. details.txt contains details of the mbed firmware pre-loaded on the board.

At one time the Mbed on-line/in-browser IDE lacked hardware programming and debug capability, so this feature was the primary means of programming Mbed boards, and debugging was painful. I believe all that has changed now and the feature is perhaps less important in development.

https://os.mbed.com/platforms/ST-Nucleo-F446RE/