NRF5340: Read FICR.DEVICEADDR and set BLE MAC random address

[Rait]

Hi all,

NRF5340
NRF Connect 2.6.0

We would like to perform the following operations on the NRF5340:
* Read FICR.DEVICEADDR (BLE random MAC is also fine).
* Set the BLE address with type random.

Seems the FICR.DEVICEADDR is only accessible by the network core, which AFAIK is not documented anywhere in the PS. So need to call bt_enable first to get the random MAC address either via bt_id_get or bt_read_static_addr.

However, using bt_id_create after BLE has been started does not apply the new MAC address for BLE comms. There seems to be a workaround for setting the public address at runtime, but this doesn't work for random. The HCI command returns SUCCESS though.
devzone.nordicsemi.com/.../setting-nrf5340-public-ble-address

Is there a solution for this specific use case?

[Sigurd Hellesvik]

Hi,

We would like to perform the following operations on the NRF5340:

What is your end goal with this?

Regards,
Sigur Hellesvik

[Rait]

End goal is to use the chip random address as MAC for both BLE and Ethernet. Both have certain requirements for the MAC address format:

*BLE: 2 most significant bits of the 48 bit MAC address must be set to 1 to identify the address as a Random Static Address.

*Ethernet: Similar story for uni/multicast / local/global addresses: 

    en.wikipedia.org/.../MAC_address

We are aware about the inprobable address conflict.

[Rait]

I've managed to change the MAC address with the code snippet you provided. It seems I was missing CONFIG_BT_SETTINGS earlier.

However, when CONFIG_BT_SETTINGS is enabled, Calling bt_id_get after bt_enable and before ble_set_mac returns id count of 0. How would I get the actual random address?

[Sigurd Hellesvik]

Without changing the mac, where would you have to call bt_id_get from to get it?

[Rait]

Didn't quite get the question. Sequence of operations is as follows:

bt_enable

bt_id_get - this fails

ble_set_mac

[Sigurd Hellesvik]

This is taking some more time to figure out than expected, but know that I am still looking into it

[Sigurd Hellesvik]

So I figure that due to ordering here, you cannot use bt_id_get to get the address.
Instead, you will have to use the HCI interface to read said address from the network core.

I tried to do this last week, but were not able to make it work.

But, the application core has to read this address over HCI at some point in its normal start-up procedure, when it sets it to the default address, so this should be possible.

I suggest that you try to do this.