RE: Getting instantly disconnected when trying to connect to BLE (0x3e with HCI)

GilDev — Fri, 27 Jun 2025 14:04:12 GMT

After multiple days of digging, it seems that I found the issue.

I had an orphaned `BT_DATA_BYTES(BT_DATA_UUID_ALL)` in my advertisement data, which looked like this:

static const struct bt_data ad[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
	BT_DATA_BYTES(BT_DATA_UUID16_ALL),
	BT_DATA_BYTES(BT_DATA_UUID128_ALL, BT_UUID_CUSTOM_SERVICE_VAL),
};

That middle line should have been entirely removed when I adapter the zephyr/peripheral sample, which looks like this:

static const struct bt_data ad[] = {
	BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
	BT_DATA_BYTES(BT_DATA_UUID16_ALL,
		      BT_UUID_16_ENCODE(BT_UUID_HRS_VAL),
		      BT_UUID_16_ENCODE(BT_UUID_BAS_VAL),
		      BT_UUID_16_ENCODE(BT_UUID_CTS_VAL)),
	BT_DATA_BYTES(BT_DATA_UUID128_ALL, BT_UUID_CUSTOM_SERVICE_VAL),
};

I guess some smartphones use Bluetooth stacks that are more strict than others, which made the whole thing crash somehow. I wonder if Android could have given me some useful logs about this…