I’ve been enjoying using the Arduino Nano Sense BLE 33 board as an all-round microcontroller for my machine learning work, but I had trouble figuring out how to programmatically write to flash memory from a sketch. I need to do this because I want to be able to download ML models over Bluetooth and then have them persist even if the user unplugs the board or resets it. After some research and experimentation I finally have a solution I’m happy with, so I’ve put an example sketch and documentation up at github.com/petewarden/arduino_nano_ble_write_flash.

The main hurdle I had to overcome was how to initialize an area of memory that would be loaded into flash when the program was first uploaded, but not touched on subsequent resets. Since modifying linker scripts isn’t recommended in the Arduino IDE, I had to come up with a home-brewed solution using const arrays and C++’s alignas() command. Thankfully it seems to work in my testing.

There’s a lot more documentation in the README and inline in the sketch, but I would warn anyone interested in this that flash has a limited number of erase/write cycles it can handle reliably, so don’t go too crazy with high-frequency changes!

I’ve now taught a lot of workshops on TinyML using the Arduino Nano Sense BLE 33 board, including the new EdX course, and while it’s a fantastic piece of technology I often have to spend a lot of time helping students figure out how to get the boards communicating with their computer. Flashing programs to the Arduino relies on having a USB connection that can use the UART serial protocol to communicate, and it turns out that there are a lot of things that can go wrong in this process. Even worse, it’s very hard to debug what’s going wrong, since the UART drivers are deep in the operating system, and vary across Windows, MacOS, and Linux computers. Students can end up getting very frustrated, even after referring to the great troubleshooting FAQ that Brian on the EdX course put together.

I’ve been trying to figure out if there’s an alternative to this approach that will make life easier. To help with that, I’ve been experimenting with how I might be able to transfer files wirelessly over the Bluetooth Low Energy protocol that the Arduino board supports, and I now have a prototype available at github.com/petewarden/ble_file_transfer. There are lots of disclaimers; it’s only a few kilobytes per second, I haven’t tested it very heavily, and it’s just a proof of concept, but I’m hoping to be able to use this to try out some approaches that will help students get started without the UART road bumps.

I also wanted to share a complete example of how to do this kind of file transfer more generally, since when I went looking for similar solutions I saw a lot of questions about how to do this but not many solutions. It’s definitely not an application that BLE is designed for, but it does seem possible to do at least. Hopefully having a version using a well-known board and WebBLE will help someone else out in the future!