Fix changing the BLE MAC address

[willwade]

We would love to be able to change MAC address of a ble device in circuitpy. Right now it’s the last thing holding us back to rewriting alll our code in py

use case. You can see some code here of how we are doing it in c https://github.com/AceCentre/morAce/blob/572e972336961dcf111b94a6fbabcda6ba3ca1be/morAce/morAce.ino#L852

imagine you use switch access on iOS. - if you want a device to change from a system switch interface to say a switch interface for a app then changing the MAC address is the only way to do it. If you don’t (& just change name, manufacturer name, device I’d etc) iOS just refuses to see it as a different device.

Another use case. We have some code that interprets morse code to hid. But then we want a user to use the same interface to use switch scanning. Doing it this way allows this.

[tannewt]

Looking more closely at our implementation, I believe this is already supported. Adapter.address is both readable and writable. So, I think you can do something like:

import _bleio
new_address = _bleio.Address(b"\x00\x00\x00\x00\x00\x00", _bleio.Address.RANDOM_STATIC)
_bleio.adapter.address = new_address

Please give it a try and let me know if it works for you.

[willwade]

Ok. Tried but getting a problem

`
import _bleio
new_address = _bleio.Address(b"\x00\x00\x00\x00\x00\x00", _bleio.Address.RANDOM_STATIC)
_bleio.adapter.address = new_address

And here its output:
code.py output:
Traceback (most recent call last):
File "code.py", line 3, in
_bleio.BluetoothError: Could not set address`

[tannewt]

Thanks for trying this @willwade. I suspect it needs to be done when no advertising or scanning is happening. Could you try it with supervisor.disable_ble_workflow() in boot.py? That will prevent CircuitPython from advertising before user code does. Thanks!

[willwade]

Hmmm. Same problem sadly

output:
code.py output:
Traceback (most recent call last):
File "code.py", line 3, in
_bleio.BluetoothError: Could not set address

[tannewt]

Thanks for testing! We'll need to take a more detailed look at this.

[hyx0329]

After digging around, I found that to compose a valid address of type RANDOM_STATIC, the address follows a format like xxxx...xxxx11, that's to say, the 2 MSBs of the address should be 1. Example code below.

address_bytes = bytearray(b'\x00\x00\x00\x00\x00\x00')
address_bytes[-1] = address_bytes[-1] | 0xC0 # now is b'\x00\x00\x00\x00\x00\xc0'
new_address = _bleio.Address(address_bytes, _bleio.Address.RANDOM_STATIC)  # <Address c0:00:00:00:00:00>
_bleio.adapter.address = new_address

[willwade]

ok so I'm perplexed. This was working but now today - same code - it isn't working. What's up with this? Is this some basic logic I'm not getting?

import _bleio

current_address = _bleio.adapter.address
print("current address:", current_address)

address_bytes = bytearray(current_address.address_bytes)
address_bytes [5] = 0xDD
new_address = _bleio.Address(address_bytes, _bleio.Address.RANDOM_STATIC)
print("new addreass:   ", new_address)

_bleio.adapter.address = new_address

print("address is set")

What I get is

current address: <Address eb:ac:4a:3c:55:2a>
new addreass:    <Address dd:ac:4a:3c:55:2a>
Traceback (most recent call last):
  File "code.py", line 11, in <module>
_bleio.BluetoothError: Could not set address

[hyx0329]

@willwade same code, works on my Makerdiary NRF52840 USB dongle, only if I disable the ble workflow by supervisor.disable_ble_workflow(). You have to call the method in boot.py(before fully boot up, I assume), otherwise you have to do a manual soft reboot(aka. reset the REPL) after that.