nRF52833 MAC Address ramdonly changing while advertising

[Learner]

Hello,

I am experiencing instances when my device (peripheral) MAC address changes randomly while the device is running and advertising.

MAC address changed during runtime from C7:2A:7D:C9:44:39 to 17:8B:E9:C7:E4:A1

MAC address reverted back from 17:8B:E9:C7:E4:A1 to C7:2A:7D:C9:44:39  after a reset/restart.

When this happens my other BLE PC application (central) cannot connect to it. However, if I reset/restart my peripheral device the original address is restored and my central can connect again. According to the Bluetooth documentation a static address does not change until a power cycle.

Below are the boot-up logs showing the 'static' address I usually see.

[00:01:16.123,107] <inf> bt_hci_core: HW Platform: Nordic Semiconductor (0x0002)
[00:01:16.123,107] <inf> bt_hci_core: HW Variant: nRF52x (0x0002)
[00:01:16.123,138] <inf> bt_hci_core: Firmware: Standard Bluetooth controller (0x00) Version 2.6 Build 99
[00:01:16.123,931] <inf> bt_hci_core: Identity: C7:2A:7D:C9:44:39 (random)
[00:01:16.123,931] <inf> bt_hci_core: HCI: version 5.2 (0x0b) revision 0x0000, manufacturer 0x05f1
[00:01:16.123,931] <inf> bt_hci_core: LMP: version 5.2 (0x0b) subver 0xffff

According to the above log from bt_hci_core,

[00:01:16.123,931] <inf> bt_hci_core: Identity: C7:2A:7D:C9:44:39 (random)

The MAC address is supposed to be random, yet every time I reset my device after I notice a change in its MAC address, it reverts back to the old address. This does not look like a random address. So, what is meant by 'random' in this context?

Note, I have had a look at other similar cases e.g. Case ID: 313249 but no explanation or solution has been provided yet.

I would appreciate it if you could respond as soon as possible. Thank you.

Kind regards

Mohamed

[Learner]

Hi Amanda,

Thank you for your support.

OK, I will add BT_LE_ADV_OPT_USE_IDENTITY  to the BT_LE_ADV_PARAM parameters.

Are you saying if I don't use the BT_LE_ADV_OPT_USE_IDENTITY option in BT_LE_ADV_PARAM then the device can randomly change its MAC address at runtime without a reset or a power cycle?

As I already stated I am seeing the device changing its MAC address without a reset or a power cycle. Is this possible?

Kind regards

Mohamed

[Amanda Hsieh]

Yes.

Yes.

If you want to advertise identity you could use BT_LE_ADV_OPT_USE_IDENTITY. 

-Amanda H.

[Learner]

Good Morning Amanda,

Thank you for your valuable support.

Please bear with me if I keep asking you the same question over and over again. This is because I believe the information contained in the link you sent me contradicts your answer. 

 https://devzone.nordicsemi.com/guides/nrf-connect-sdk-guides/b/software/posts/building-a-ble-application-on-ncs-comparing-and-contrasting-to-softdevice-based-ble-applications 

According to the link above,

"... Note if you want to advertise using local identity (static address not new address every time you reset) you should use BT_LE_ADV_OPT_USE_IDENTITY option. "

This suggests that if I don't use BT_LE_ADV_OPT_USE_IDENTITY option then the random static address can change but only after a reset. Or am I understanding this wrong?

Kind regards

Mohamed

[Amanda Hsieh]

Learner said:

This suggests that if I don't use BT_LE_ADV_OPT_USE_IDENTITY option then the random static address can change but only after a reset.

That's correct. Do you still see it change the address with this option?

-Amanda H.

[Learner]

Good Morning Amanda,

First, the MAC address change I reported does not happen often. In fact my device can go on for weeks and months without changing its MAC address.

Second, when it does change its MAC address it does it without going through a reset.

Finally, I have added the option BT_LE_ADV_OPT_USE_IDENTITY as you suggested. I will be monitoring this in the coming weeks and months.

Kind regards

Mohamed