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

[Amanda Hsieh]

Hi, 

What type of address would you like to set? Bluetooth Low Energy comes with different address types, which you can read about in our DevAcademy course: https://academy.nordicsemi.com/topic/bluetooth-address/ 

Only public address type is liable to a fee (to the IEEE registration authority), random addresses can be used freely. The default address used by the Bluetooth Stacks in nRF52833 is a random static address obtained from the DEVICEADDR[n] FICR registers (random number programmed during chip manufacturing).

If you want to set Resolvable Private Addresses, you could use CONFIG_BT_PRIVACY. 

Regards,
Amanda H.

[Learner]

Hi Amanda,

Thank you for your prompt response.

I do not want to set the MAC address. I am happy to use the default address.

Amanda Hsieh said:

The default address used by the Bluetooth Stacks in nRF52833 is a random static address obtained from the DEVICEADDR[n] FICR registers (random number programmed during chip manufacturing).

According to Nordic's Academy Bluetooth-address page,

"A random static address can be allocated and then fixed throughout the lifetime of the device. It can be altered at bootup, but not during runtime. "

So, why am I seeing the random static MAC address of my device changing at runtime?

Then when I restart (hard reset) the device it reverts back to the original MAC address.

As far as I can make out, I am not doing anything in my application code to change it.

Please explain what could be happening.

Also, according to Nordic's documentation,

"Factory information configuration registers (FICR) are pre-programmed in factory and cannot be erased by the user. "

However, you said in your reply a random static address can be changed at bootup. Please explain how.

Thank you.

Kind regards

Mohamed

[Amanda Hsieh]

Hi, 

Learner said:

why am I seeing the random static MAC address of my device changing at runtime?

What is your application? Do you mean in the advertising? If so, how do you set the BT_LE_ADV_PARAM? 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. Check the Advertising section in this guide.

Learner said:

"Factory information configuration registers (FICR) are pre-programmed in factory and cannot be erased by the user. "

However, you said in your reply a random static address can be changed at bootup. Please explain how.

You can set the application to use the random static address at bootuping the application. 

-Amanda H.

[Learner]

Good Morning Amanda,

Amanda Hsieh said:

What is your application? Do you mean in the advertising? If so, how do you set the BT_LE_ADV_PARAM?

Yes, I am referring to the MAC address in the advertising. My device is a connectable peripheral that other devices should be able to connect to over BLE.

This is what I am doing to set the advertising parameters,

#define BT_LE_ADV_CONN_SLOW                BT_LE_ADV_PARAM((BT_LE_ADV_OPT_CONNECTABLE | BT_LE_ADV_OPT_SCANNABLE), BT_GAP_ADV_SLOW_INT_MIN, BT_GAP_ADV_SLOW_INT_MAX, NULL)

#define BT_LE_ADV_CONN_FAST                  BT_LE_ADV_PARAM((BT_LE_ADV_OPT_CONNECTABLE | BT_LE_ADV_OPT_SCANNABLE), BT_GAP_ADV_FAST_INT_MIN_2, BT_GAP_ADV_FAST_INT_MAX_2, NULL)

/* ble_ad[] Can be up to 29 bytes */                                                                                                                                                         static uint8_t ble_ad[HB_BLE_AD_BUFF_SIZE_MAX] = { 0U };

/* legacy advertisements up to 31 bytes Max */                                                                                                                                     static const struct bt_data ad[] = { BT_DATA(BT_DATA_MANUFACTURER_DATA, &ble_ad[0], sizeof(ble_ad)) }; 

/* ble_sd[] Can be up to 29 bytes */                                                                                                                                                         static uint8_t ble_sd[HB_BLE_SD_BUFF_SIZE_MAX] = { 0U }; 

/* legacy advertisements up to 31 bytes Max */
static const struct bt_data sd[] = { BT_DATA(BT_DATA_MANUFACTURER_DATA, &ble_sd[0], sizeof(ble_sd)) }; 

...

/* Start advertising */                                                                                                                                bt_le_adv_start(BT_LE_ADV_CONN_SLOW, ad, ARRAY_SIZE(ad), sd, ARRAY_SIZE(sd));

Amanda Hsieh said:

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. 

Sometimes, I am seeing the advertising MAC address changing at runtime without the device going through a reset. According to the documentation this should not happen. Then when I reset the device it reverts back to its old address. 

Can you please explain what could be causing this?

Learner said:

According to Nordic's Academy Bluetooth-address page,

"A random static address can be allocated and then fixed throughout the lifetime of the device. It can be altered at bootup, but not during runtime. "

I am still unclear about how an application can change a static random address at boot-up. Please clarify.

Kind regards

Mohamed

[Amanda Hsieh]

As I explained in the previous reply, you should use BT_LE_ADV_OPT_USE_IDENTITY option in the BT_LE_ADV_PARAM. Check the Advertising section in this guide.

[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

[Amanda Hsieh]

Hi Mohamed, 

I got it.

Please don't hesitate to contact me if you need further help.

Regards,
Amanda H.

[Learner]

Hi Amanda,

Thank you. 

But you still have not commented on why, before I added the option BT_LE_ADV_OPT_USE_IDENTITY, my device was sometimes changing its MAC address without going through a reset.                              According to Nordic's documentation this is not the expected behaviour.

Kind regards

Mohamed