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]

Hi,

Thanks for the reply. As already mentioned we would like to modify the MAC address to also follow the guidelines to Ethernet MAC on top of BLE MAC. So the operation looks like that:

[Sigurd Hellesvik]

I have found that it works like this:

When you first start the device, the BLE host on the app core will retrieve the address from the network core. This addr will then be saved to app core flash using the Settings module.

When you start the app and call settings_load() the addr will be loaded from settings.

From bt_id_reset():
"the default identity (BT_ID_DEFAULT) cannot be reset"

This means that to change the MAC, you must add a second addr and advertise the second addr instead of the default ID.

It should go something like this:

1. call settings_load()

2. call bt_id_create()

3. Configure advertising to use your MAC instead of the default one.

You might have to configure CONFIG_BT_ID_MAX to have more IDs.

Possibly the Bluetooth: Peripheral Identity may be of some help.

Was this answer what you are looking for?

[Rait]

Thanks for the update. I did try the settings load and it made no difference.

The device in question is a BLE central, so it won't do any advertising. The incorrect address is seen on the peripheral side.

[Sigurd Hellesvik]

Ah, it is a central
For clarity: When you say, "The incorrect address is seen on the peripheral side.", exactly how do you get the MAC at the peripheral side?

[Rait]

bt_conn_cb.connected -> bt_conn_get_dst

[Sigurd Hellesvik]

Figuring this out is taking a hit longer than expected, but I am still on  it

[Sigurd Hellesvik]

A colleague suggests  nRF5340 - setting public bt address .

Does that do what you need?

[Rait]

Already tried that as mentioned in the original post. Didn't work.

[Sigurd Hellesvik]

I tried the stuff in that post on our BLE UART Central sample.

Here is what I changed:

diff --git a/samples/bluetooth/central_uart/src/main.c b/samples/bluetooth/central_uart/src/main.c
index 756b8d136..9a7ea5002 100644
--- a/samples/bluetooth/central_uart/src/main.c
+++ b/samples/bluetooth/central_uart/src/main.c
@@ -17,6 +17,7 @@
 
 #include <zephyr/bluetooth/bluetooth.h>
 #include <zephyr/bluetooth/hci.h>
+#include <zephyr/bluetooth/hci_vs.h>
 #include <zephyr/bluetooth/conn.h>
 #include <zephyr/bluetooth/uuid.h>
 #include <zephyr/bluetooth/gatt.h>
@@ -548,6 +549,28 @@ static struct bt_conn_auth_info_cb conn_auth_info_callbacks = {
 	.pairing_failed = pairing_failed
 };
 
+
+
+void ble_set_mac(bt_addr_t* addr)
+{
+	struct net_buf *buf;
+	int rc;
+
+	buf = bt_hci_cmd_create(BT_HCI_OP_VS_WRITE_BD_ADDR, sizeof(*addr));
+	if (!buf) {
+		LOG_ERR("failed to create buffer [%d]", -ENOBUFS);
+	}
+
+	net_buf_add_mem(buf, addr, sizeof(*addr));
+
+	rc = bt_hci_cmd_send_sync(BT_HCI_OP_VS_WRITE_BD_ADDR, buf, NULL);
+	if (rc) {
+		LOG_ERR("failed to set BT address [%d]", rc);
+	}
+}
+
+
+
 int main(void)
 {
 	int err;
@@ -570,6 +593,20 @@ int main(void)
 		return 0;
 	}
 	LOG_INF("Bluetooth initialized");
+/* check for public address in UICR.OPT area */
+
+  LOG_INF("setting public address retrieved from UICR");
+
+  bt_addr_t addr;
+
+  addr.val[0] = 2;
+  addr.val[1] = 2;
+  addr.val[2] = 2;
+  addr.val[3] = 2;
+  addr.val[4] = 2;
+  addr.val[5] = 2;
+  ble_set_mac(&addr);
+
 
 	if (IS_ENABLED(CONFIG_SETTINGS)) {
 		settings_load();

And here is the logs from the peripheral UART sample from before and after connecting to the central

Could you also test this with these samples on your side?

[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?