RSSI value through the BLE connection process in nRF connect SDK

RE: RSSI value through the BLE connection process in nRF connect SDK

jyu10 — Wed, 03 Sep 2025 13:38:24 GMT

Hi Einar,

Do you know if it is possible to modify the script to just query the individual frequencies that bluetooth LE communicates for RSSI values without having to connect with devices?

RE: RSSI value through the BLE connection process in nRF connect SDK

LongQi — Tue, 04 Jun 2024 08:53:57 GMT

I still got 127 after I use the work queue unless I add some dealy in check_rssi_and_disconnect() or call check_rssi_and_disconnect() from main loop.

In the both situation, printk("fail getting conn handle") did not get exectuted.

RE: RSSI value through the BLE connection process in nRF connect SDK

Einar Thorsrud — Thu, 02 May 2024 10:51:06 GMT

Hi,

I have modified the Zephyr Bluetooth central sample to print the RSSI found in the connection before disconnecting (it also prints the RSSI for the advertising packet as that is part of the official sample). You just need to add the two Kconigs you have allready included, and use with this .c file:

devzone.nordicsemi.com/.../0245.main.c

RE: RSSI value through the BLE connection process in nRF connect SDK

Pranathi CH — Thu, 02 May 2024 05:21:22 GMT

Hi Einar,

I tried to call it in the main loop as per the thread discussion, but I guess I didn't get it right and I am confused on what exactly to do, can you explain me clearly how to do it?

RE: RSSI value through the BLE connection process in nRF connect SDK

Einar Thorsrud — Tue, 30 Apr 2024 13:06:57 GMT

Hi,

You cannot read the RSSI in the connected callback. You need to wait until it has returned and call it later. See this thread for details.

RE: RSSI value through the BLE connection process in nRF connect SDK

Pranathi CH — Tue, 30 Apr 2024 11:40:32 GMT

Hi Einar,

I was trying in the meanwhile I added the prj.conf

CONFIG_BT_CTLR_ADVANCED_FEATURES=y

CONFIG_BT_CTLR_CONN_RSSI=y

Now I am getting a constant value of 127 as the RSSI value.

Atleast I am not getting the read error anymore....but am I missing something so I am only getting a 127 constant value every time I run the program?

Thanks,

Pranathi

RE: RSSI value through the BLE connection process in nRF connect SDK

Pranathi CH — Tue, 30 Apr 2024 10:47:33 GMT

Hi Einar,

I am explicitely able to connect to the BLE device with my Dev kit without scanning. And to read RSSI, I have added the function read_conn_rssi() in my code and called it.

I am getting the Read RSSI error as -5, which is internally mentioned as I/O error.

CODE:

static void read_conn_rssi(uint16_t handle, int8_t *rssi)
{
	struct net_buf *buf, *rsp = NULL;
	struct bt_hci_cp_read_rssi *cp;
	struct bt_hci_rp_read_rssi *rp;

	int err;

	buf = bt_hci_cmd_create(BT_HCI_OP_READ_RSSI, sizeof(*cp));
	if (!buf) {
		printk("Unable to allocate command buffer\n");
		return;
	}

	cp = net_buf_add(buf, sizeof(*cp));
	cp->handle = sys_cpu_to_le16(handle);

	err = bt_hci_cmd_send_sync(BT_HCI_OP_READ_RSSI, buf, &rsp);
	if (err) {
		uint8_t reason = rsp ?
			((struct bt_hci_rp_read_rssi *)rsp->data)->status : 0;
		printk("Read RSSI err: %d reason 0x%02x\n", err, reason);
		return;
	}

	rp = (void *)rsp->data;
	*rssi = rp->rssi;

	net_buf_unref(rsp);
}

static void connected(struct bt_conn *conn, uint8_t err)
{
    char addr[BT_ADDR_LE_STR_LEN];

	
     
    bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));

    if (err) {
        printk("Failed to connect to %s (%u)\n", addr, err);

        bt_conn_unref(default_conn);
        default_conn = NULL;
	}
	else
	{

	}

    if (conn != default_conn) {
        return;
    }
    printk("\nConnected: %s\n", addr);
	int8_t rssi = 0xFF;
	// printk("\nRSSI:%d\n",rssi);
	read_conn_rssi(default_conn_handle, &rssi);
	printk("Connected (%d) - RSSI = %d\n",default_conn_handle, rssi);
}

OUTPUT:

How do I solve it?

Thanks,

Pranathi

RE: RSSI value through the BLE connection process in nRF connect SDK

Einar Thorsrud — Mon, 29 Apr 2024 11:48:31 GMT

Hi Pranathi,

To be clear, there is no way to connect without scanning. When you excplicitly attemt to connect to a specific BLE address, what happens is that scanning is started, and when you receive a connectable advertising packet from the specified address, the BLE stack will connect to it.

With that out of the way, to obtain the RSSI in a connection you can use BT_HCI_OP_READ_RSSI. You can find an example of that in read_conn_rssi() in zephyr/samples/bluetooth/hci_pwr_ctrl/src/main.c.

Einar