public MAC address on nrf52840

[stef]

when running this code on a xiao_ble which is based on the nrf52840:

  int err = bt_enable(NULL);
  if (err) {
     LOG_WRN("Failed to enable bluetooth: %d", err);
     return err;
  }

   err = bt_le_adv_start(BT_LE_ADV_PARAM((BT_LE_ADV_OPT_CONN |
                                     BT_LE_ADV_OPT_USE_IDENTITY), /* Connectable advertising and use identity address */
                                     BT_GAP_ADV_FAST_INT_MIN_1, /* Min Advertising Interval 30 ms */
                                     BT_GAP_ADV_FAST_INT_MAX_1, /* Max Advertising Interval 60 ms */
                                     NULL), /* Set to NULL for undirected advertising */
                         ad, ARRAY_SIZE(ad), sd, ARRAY_SIZE(sd));
   if (err) {
      LOG_ERR("Advertising failed to start (err %d)", err);
   } else {
      LOG_DBG("Advertising successfully started");
   }

  char addr_s[BT_ADDR_LE_STR_LEN];
  bt_addr_le_t addr = {0};

  struct bt_le_oob oob;
  err = bt_le_oob_get_local(BT_ID_DEFAULT, &oob);
  if (err) {
    LOG_ERR("Failed to get OOB data (err %d)\n", err);
    return err;
  }
  bt_addr_le_to_str(&oob.addr, addr_s, sizeof(addr_s));
  //size_t count = 1;
  //bt_id_get(&addr, &count);
  //bt_addr_le_to_str(&addr, addr_s, sizeof(addr_s));
  LOG_INF("MAC address: %s", addr_s);

i get mac addresses like this:

D5:0B:46:52:6B:FA (random)

and similar with the commented out bt_id_get() variant.

my prj.cfg is something like this:

CONFIG_BT=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_ZEPHYR_NUS=y
CONFIG_BT_MAX_CONN=2
CONFIG_BT_MAX_PAIRED=1
CONFIG_BT_DEVICE_NAME="test ble"
CONFIG_BT_EXT_ADV=y
CONFIG_BT_DEBUG_NONE=y
CONFIG_BT_ASSERT=n
CONFIG_BT_DATA_LEN_UPDATE=n
CONFIG_BT_PHY_UPDATE=n
CONFIG_BT_GATT_CACHING=n
CONFIG_BT_GATT_SERVICE_CHANGED=n
CONFIG_BT_GAP_PERIPHERAL_PREF_PARAMS=n
CONFIG_BT_HCI_VS=n
# Disable Bluetooth controller features not needed
CONFIG_BT_CTLR_PRIVACY=n
CONFIG_BT_PRIVACY=n
CONFIG_BT_CTLR_PHY_2M=n

# Reduce Bluetooth buffers
CONFIG_BT_BUF_EVT_DISCARDABLE_COUNT=1
#CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE=43
CONFIG_BT_BUF_EVT_DISCARDABLE_SIZE=58
CONFIG_BT_BUF_EVT_RX_COUNT=4

CONFIG_BT_CONN_TX_MAX=3
CONFIG_BT_L2CAP_TX_BUF_COUNT=2
CONFIG_BT_ATT_TX_COUNT=2
CONFIG_BT_BUF_ACL_TX_COUNT=3
CONFIG_BT_BUF_ACL_TX_SIZE=27

the same code worked well with an esp32s3.

i tried to search online for this, but only found old posts in the nordicsemi support site, some slightly relevant github issues, and other stuff that didn't get me further, i grepped the samples. but it all looks like my code. what am i missing? where is my cognitive blind spot? or is this some kind of bug, or under-documented feature?

thanks for any pointers!

[nordicjm]

The random address is expected. To have a public address, you would need to have bought an identifier and block of addresses

[stef]

so just to clarify espressif bought an identifier/block of addresses for my device and it is included automatically or are they doing something illegal? and there is no way to have for dev purposes a public address? this is a small / private hobby project.

[stef]

but in the above example i do have that set in my prj.conf:

CONFIG_BT_CTLR_PRIVACY=n
CONFIG_BT_PRIVACY=n

[nordicjm]

Hmm that is odd, been a long time since I looked but perhaps the address is generated and stored, try enabling settings and the bluetooth setting Kconfig (which depends on settings)

[stef]

you mean CONFIG_BT_SETTINGS=y? i'll try that.

[stef]

i enabled CONFIG_BT_SETTINGS=y but still the same behaviour.

[stef]

trying to make a minimized reproduction of the problem. stay tuned.

[stef]

i made a repro repo here: https://github.com/stef/nrf_staticmac - what am i doing wrong?