Create first BLE-only board, Micro:Bit v2

[tannewt]

This fixes build issues with USB off, tweaks the README to allow
for BLE-only boards and adds the Micro:Bit v2 definition.

Fixes #4546 Fixes #4680

[jepler]

The debug printing changes looked weird, but if it's intended then it's OK to merge. No testing performed.

[tyomitch]

@tannewt I see that the Makefile now relies on a script hexmerge.py which is not in the source tree.
Where is it supposed to be taken from?

[jerryneedell]

hexmerge.py is part of the intelhex package.
I installed it via pip3 install intelhex

[jerryneedell]

I would be happy to help with testing this build, but I am completely baffled about how to use the board.
I have occasionally managed to get the serial device to spit out the CP version info (see screenshot), but nothing else. I can see the CIRCPY BLE device but have made no progress connecting to it.
Should I be able to get to the REPL via something like screen? I can connect, but get no responses....
Clearly, I am missing something. Are there any instructions for using code.circuitpython.org?

[tannewt]

@tannewt I see that the Makefile now relies on a script hexmerge.py which is not in the source tree.
Where is it supposed to be taken from?

We store python build dependencies in requirements-dev.txt so you should be able to pip install -r requirements-dev.txt to get everything you need.

[tannewt]

I would be happy to help with testing this build, but I am completely baffled about how to use the board.
I have occasionally managed to get the serial device to spit out the CP version info (see screenshot), but nothing else. I can see the CIRCPY BLE device but have made no progress connecting to it.
Should I be able to get to the REPL via something like screen? I can connect, but get no responses....
Clearly, I am missing something. Are there any instructions for using code.circuitpython.org?

Thanks for trying this out! I know its super early for apps on the host side.

The USB serial is a conversion of the UART debug output. I'm going to turn this off shortly to make it clearer that this is only meant for BLE use. (Serial is really nice for debugging though.)

The most instructions I've written are on the page itself. I should make it clearer that BLE stuff will only work with Mac Chrome and Android Chrome. Chrome OS and Windows don't support secure characteristics yet (the chrome folks are working on it now I think.)

I think there are some crashes on the device side too unfortunately. I was trying to debug it but ran into debugger and binary blob issues.

So, don't spend too much time hitting a wall with this. It's still very early and will get better as the host side matures.

[jerryneedell]

I am using an M1 Mac -- I can try going back to an Intel Mac as well if that may be a problem.

Same behavior on Intel Mac

[spoelstraethan]

@tannewt would there be many changes for the micro:bit v1 to run CircuitPython or is the slightly lower spec hardware not capable?

This is a good comparison of both the new features and the processor/memory differences.

https://kitronik.co.uk/blogs/resources/explore-micro-bit-v1-microbit-v2-differences

[tyomitch]

@spoelstraethan I doubt CircuitPython can be squeezed into 16 KB RAM; even 32 KB boards are a very tight fit.

[tannewt]

@tannewt would there be many changes for the micro:bit v1 to run CircuitPython or is the slightly lower spec hardware not capable?

No, I don't plan on supporting the v1. As tyomitch points out, the change from 128k ram to 16k ram is a huge downgrade. We regularly have folks frustrated with the 32k ram on the SAMD21.