Dynamic BLE TX Power Config Fails (nRF5340-DK)

[diegonovo02]

Hello everyone,

I’m working on a project using two nRF5340-DK boards to measure throughput and RSSI while dynamically changing the PHY and TX power. I started from the official throughput example and added:

• RSSI measurement (I think this works)

• A shell command config pwr <value in dBm> to adjust the transmit power, implemented similarly to the PHY-change command

The problem is that power adjustment only works at the default 0 dBm. If I try any other value, the command runs but returns an error, so it looks like my implementation isn’t actually applying the new power setting.

When I set the transmit power to anything other than 0 dBm, I get this output:

Here’s what I’ve changed (all code is available on GitHub):

1. cmds.c

   • Added a default TX power of 0 dBm

   • Registered the config pwr subcommand in SHELL_STATIC_SUBCMD_SET_CREATE

   • Implemented the pwr_cmd function to parse and store the dBm value

2. main.h / main.c

   • Declared extern int8_t g_tx_power; in main.h and defined it in main.c

   • Modified connection_configuration_set() to apply g_tx_power to the BLE connection

You can find the full code here:
https://github.com/diegonovo02/prueba_ble

Does anyone know why only 0 dBm works, and how I can get other power levels to apply correctly? Any pointers or fixes would be hugely appreciated!

Thanks in advance,
Diego

[Sigurd]

Hi!

Try this main.c

/*
 * Copyright (c) 2018 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
 */

#include <zephyr/kernel.h>
#include <zephyr/console/console.h>
#include <zephyr/sys/printk.h>
#include <string.h>
#include <stdlib.h>
#include <zephyr/types.h>

#include <zephyr/bluetooth/bluetooth.h>
#include <zephyr/bluetooth/crypto.h>
#include <zephyr/bluetooth/conn.h>
#include <zephyr/bluetooth/gatt.h>
#include <zephyr/bluetooth/hci.h>
#include <zephyr/bluetooth/uuid.h>
#include <bluetooth/services/throughput.h>
#include <bluetooth/scan.h>
#include <bluetooth/gatt_dm.h>

#include <zephyr/shell/shell_uart.h>

#include <dk_buttons_and_leds.h>

#include <zephyr/net/buf.h>
#include <zephyr/sys/byteorder.h>
#include <zephyr/bluetooth/hci_vs.h>

#include "main.h"

int8_t g_tx_power = 0;

#define DEVICE_NAME	CONFIG_BT_DEVICE_NAME
#define DEVICE_NAME_LEN (sizeof(DEVICE_NAME) - 1)
#define INTERVAL_MIN	0x6	/* 6 units, 7.5 ms, only used to setup connection */
#define INTERVAL_MAX	0x6	/* 6 units, 7.5 ms, only used to setup connection */

#define THROUGHPUT_CONFIG_TIMEOUT K_SECONDS(20)

static K_SEM_DEFINE(throughput_sem, 0, 1);

static volatile bool data_length_req;
static volatile bool test_ready;
static struct bt_conn *default_conn;
static uint16_t default_conn_handle;
static struct bt_throughput throughput;
static const struct bt_uuid *uuid128 = BT_UUID_THROUGHPUT;
static struct bt_gatt_exchange_params exchange_params;
static struct bt_le_conn_param *conn_param =
	BT_LE_CONN_PARAM(INTERVAL_MIN, INTERVAL_MAX, 0, 400);

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_UUID128_ALL,
		0xBB, 0x4A, 0xFF, 0x4F, 0xAD, 0x03, 0x41, 0x5D,
		0xA9, 0x6C, 0x9D, 0x6C, 0xDD, 0xDA, 0x83, 0x04),
};

static const struct bt_data sd[] = {
	BT_DATA(BT_DATA_NAME_COMPLETE, DEVICE_NAME, DEVICE_NAME_LEN),
};

static void button_handler_cb(uint32_t button_state, uint32_t has_changed);

static const char *phy2str(uint8_t phy)
{
	switch (phy) {
	case 0: return "No packets";
	case BT_GAP_LE_PHY_1M: return "LE 1M";
	case BT_GAP_LE_PHY_2M: return "LE 2M";
	case BT_GAP_LE_PHY_CODED: return "LE Coded";
	default: return "Unknown";
	}
}

static void instruction_print(void)
{
	printk("\nType 'config' to change the configuration parameters.\n");
	printk("You can use the Tab key to autocomplete your input.\n");
	printk("Type 'run' when you are ready to run the test.\n");
}

static int read_conn_rssi_val(uint16_t handle, int8_t *rssi_out)
{
    struct net_buf *cmd, *rsp;
    struct bt_hci_cp_read_rssi *cp;
    struct bt_hci_rp_read_rssi *rp;
    int err;

    cmd = bt_hci_cmd_create(BT_HCI_OP_READ_RSSI, sizeof(*cp));
    if (!cmd) {
        printk("ERR: HCI cmd buffer\n");
        return -ENOMEM;
    }

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

    err = bt_hci_cmd_send_sync(BT_HCI_OP_READ_RSSI, cmd, &rsp);
    if (err) {
        printk("ERR: HCI_READ_RSSI %d\n", err);
        return err;
    }

    rp = (struct bt_hci_rp_read_rssi *)rsp->data;
    *rssi_out = rp->rssi;
    net_buf_unref(rsp);

    return 0;
}

void scan_filter_match(struct bt_scan_device_info *device_info,
		       struct bt_scan_filter_match *filter_match,
		       bool connectable)
{
	char addr[BT_ADDR_LE_STR_LEN];

	bt_addr_le_to_str(device_info->recv_info->addr, addr, sizeof(addr));

	printk("Filters matched. Address: %s connectable: %d\n",
		addr, connectable);
}

void scan_filter_no_match(struct bt_scan_device_info *device_info,
			  bool connectable)
{
	char addr[BT_ADDR_LE_STR_LEN];

	bt_addr_le_to_str(device_info->recv_info->addr, addr, sizeof(addr));

	printk("Filter not match. Address: %s connectable: %d\n",
				addr, connectable);
}

void scan_connecting_error(struct bt_scan_device_info *device_info)
{
	printk("Connecting failed\n");
}

BT_SCAN_CB_INIT(scan_cb, scan_filter_match, scan_filter_no_match,
		scan_connecting_error, NULL);

static void exchange_func(struct bt_conn *conn, uint8_t att_err,
			  struct bt_gatt_exchange_params *params)
{
	struct bt_conn_info info = {0};
	int err;

	printk("MTU exchange %s\n", att_err == 0 ? "successful" : "failed");

	err = bt_conn_get_info(conn, &info);
	if (err) {
		printk("Failed to get connection info %d\n", err);
		return;
	}

	if (info.role == BT_CONN_ROLE_CENTRAL) {
		instruction_print();
		test_ready = true;
	}
}

static void discovery_complete(struct bt_gatt_dm *dm,
			       void *context)
{
	int err;
	struct bt_throughput *throughput = context;

	printk("Service discovery completed\n");

	bt_gatt_dm_data_print(dm);
	bt_throughput_handles_assign(dm, throughput);
	bt_gatt_dm_data_release(dm);

	exchange_params.func = exchange_func;

	err = bt_gatt_exchange_mtu(default_conn, &exchange_params);
	if (err) {
		printk("MTU exchange failed (err %d)\n", err);
	} else {
		printk("MTU exchange pending\n");
	}
}

static void discovery_service_not_found(struct bt_conn *conn,
					void *context)
{
	printk("Service not found\n");
}

static void discovery_error(struct bt_conn *conn,
			    int err,
			    void *context)
{
	printk("Error while discovering GATT database: (%d)\n", err);
}

struct bt_gatt_dm_cb discovery_cb = {
	.completed         = discovery_complete,
	.service_not_found = discovery_service_not_found,
	.error_found       = discovery_error,
};

static void connected(struct bt_conn *conn, uint8_t hci_err)
{
	struct bt_conn_info info = {0};
	int err;

	if (hci_err) {
		if (hci_err == BT_HCI_ERR_UNKNOWN_CONN_ID) {
			/* Canceled creating connection */
			return;
		}

		printk("Connection failed, err 0x%02x %s\n", hci_err, bt_hci_err_to_str(hci_err));
		return;
	}

	if (default_conn) {
		printk("Connection exists, disconnect second connection\n");
		bt_conn_disconnect(conn, BT_HCI_ERR_REMOTE_USER_TERM_CONN);
		return;
	}

	default_conn = bt_conn_ref(conn);

	err = bt_conn_get_info(default_conn, &info);
	if (err) {
		printk("Failed to get connection info %d\n", err);
		return;
	}

	printk("Connected as %s\n",
	       info.role == BT_CONN_ROLE_CENTRAL ? "central" : "peripheral");
	printk("Conn. interval is %u units\n", info.le.interval);

	if (info.role == BT_CONN_ROLE_PERIPHERAL) {
		err = bt_conn_set_security(conn, BT_SECURITY_L2);
		if (err) {
			printk("Failed to set security: %d\n", err);
		}
	}
}

void security_changed(struct bt_conn *conn, bt_security_t level, enum bt_security_err security_err)
{
	printk("Security changed: level %i, err: %i %s\n", level, security_err,
	       bt_security_err_to_str(security_err));

	if (security_err != 0) {
		printk("Failed to encrypt link\n");
		bt_conn_disconnect(conn, BT_HCI_ERR_PAIRING_NOT_SUPPORTED);
		return;
	}

	struct bt_conn_info info = {0};
	int err;

	err = bt_conn_get_info(default_conn, &info);
	if (info.role == BT_CONN_ROLE_CENTRAL) {
		err = bt_gatt_dm_start(default_conn,
				       BT_UUID_THROUGHPUT,
				       &discovery_cb,
				       &throughput);
		if (err) {
			printk("Discover failed (err %d)\n", err);
		}
	}
}

static void scan_init(void)
{
	int err;
	struct bt_le_scan_param scan_param = {
		.type = BT_LE_SCAN_TYPE_PASSIVE,
		.options = BT_LE_SCAN_OPT_FILTER_DUPLICATE,
		.interval = 0x0010,
		.window = 0x0010,
	};

	struct bt_scan_init_param scan_init = {
		.connect_if_match = 1,
		.scan_param = &scan_param,
		.conn_param = conn_param
	};

	bt_scan_init(&scan_init);
	bt_scan_cb_register(&scan_cb);

	err = bt_scan_filter_add(BT_SCAN_FILTER_TYPE_UUID, uuid128);
	if (err) {
		printk("Scanning filters cannot be set\n");

		return;
	}

	err = bt_scan_filter_enable(BT_SCAN_UUID_FILTER, false);
	if (err) {
		printk("Filters cannot be turned on\n");
	}
}

static void scan_start(void)
{
	int err;

	err = bt_scan_start(BT_SCAN_TYPE_SCAN_PASSIVE);
	if (err) {
		printk("Starting scanning failed (err %d)\n", err);
		return;
	}
}

static void adv_start(void)
{
	const struct bt_le_adv_param *adv_param =
		BT_LE_ADV_PARAM(BT_LE_ADV_OPT_CONNECTABLE |
				BT_LE_ADV_OPT_ONE_TIME,
				BT_GAP_ADV_FAST_INT_MIN_2,
				BT_GAP_ADV_FAST_INT_MAX_2,
				NULL);
	int err;

	err = bt_le_adv_start(adv_param, ad, ARRAY_SIZE(ad), sd,
			      ARRAY_SIZE(sd));
	if (err) {
		printk("Failed to start advertiser (%d)\n", err);
		return;
	}
}

static void disconnected(struct bt_conn *conn, uint8_t reason)
{
	struct bt_conn_info info = {0};
	int err;

	printk("Disconnected, reason 0x%02x %s\n", reason, bt_hci_err_to_str(reason));

	test_ready = false;
	if (default_conn) {
		bt_conn_unref(default_conn);
		default_conn = NULL;
	}

	err = bt_conn_get_info(conn, &info);
	if (err) {
		printk("Failed to get connection info (%d)\n", err);
		return;
	}

	/* Re-connect using same roles */
	if (info.role == BT_CONN_ROLE_CENTRAL) {
		scan_start();
	} else {
		adv_start();
	}
}

static bool le_param_req(struct bt_conn *conn, struct bt_le_conn_param *param)
{
	printk("Connection parameters update request received.\n");
	printk("Minimum interval: %d, Maximum interval: %d\n",
	       param->interval_min, param->interval_max);
	printk("Latency: %d, Timeout: %d\n", param->latency, param->timeout);

	return true;
}

static void le_param_updated(struct bt_conn *conn, uint16_t interval,
			     uint16_t latency, uint16_t timeout)
{
	printk("Connection parameters updated.\n"
	       " interval: %d, latency: %d, timeout: %d\n",
	       interval, latency, timeout);

	k_sem_give(&throughput_sem);
}

static void le_phy_updated(struct bt_conn *conn,
			   struct bt_conn_le_phy_info *param)
{
	printk("LE PHY updated: TX PHY %s, RX PHY %s\n",
	       phy2str(param->tx_phy), phy2str(param->rx_phy));

	k_sem_give(&throughput_sem);
}

static void le_data_length_updated(struct bt_conn *conn,
				   struct bt_conn_le_data_len_info *info)
{
	if (!data_length_req) {
		return;
	}

	printk("LE data len updated: TX (len: %d time: %d)"
	       " RX (len: %d time: %d)\n", info->tx_max_len,
	       info->tx_max_time, info->rx_max_len, info->rx_max_time);

	data_length_req = false;
	k_sem_give(&throughput_sem);
}

static uint8_t throughput_read(const struct bt_throughput_metrics *met)
{
	printk("[peer] received %u bytes (%u KB)"
	       " in %u GATT writes at %u bps\n",
	       met->write_len, met->write_len / 1024, met->write_count,
	       met->write_rate);

	k_sem_give(&throughput_sem);

	return BT_GATT_ITER_STOP;
}

static void throughput_received(const struct bt_throughput_metrics *met)
{
	static uint32_t kb;

	if (met->write_len == 0) {
		kb = 0;
		printk("\n");

		return;
	}

	if ((met->write_len / 1024) != kb) {
		kb = (met->write_len / 1024);
		printk("=");
	}
}

static void throughput_send(const struct bt_throughput_metrics *met)
{
	printk("\n[local] received %u bytes (%u KB)"
		" in %u GATT writes at %u bps\n",
		met->write_len, met->write_len / 1024,
		met->write_count, met->write_rate);
}

static const struct bt_throughput_cb throughput_cb = {
	.data_read = throughput_read,
	.data_received = throughput_received,
	.data_send = throughput_send
};

static struct button_handler button = {
	.cb = button_handler_cb,
};

void select_role(bool is_central)
{
	int err;
	static bool role_selected;

	if (role_selected) {
		printk("\nCannot change role after it was selected once.\n");
		return;
	} else if (is_central) {
		printk("\nCentral. Starting scanning\n");
		scan_start();
	} else {
		printk("\nPeripheral. Starting advertising\n");
		adv_start();
	}

	role_selected = true;

	/* The role has been selected, button are not needed any more. */
	err = dk_button_handler_remove(&button);
	if (err) {
		printk("Button disable error: %d\n", err);
	}
}

static void button_handler_cb(uint32_t button_state, uint32_t has_changed)
{
	ARG_UNUSED(has_changed);

	if (button_state & DK_BTN1_MSK) {
		select_role(true);
	} else if (button_state & DK_BTN2_MSK) {
		select_role(false);
	}
}

static void buttons_init(void)
{
	int err;

	err = dk_buttons_init(NULL);
	if (err) {
		printk("Buttons initialization failed.\n");
		return;
	}

	/* Add dynamic buttons handler. Buttons should be activated only when
	 * during the board role choosing.
	 */
	dk_button_handler_add(&button);
}



static int connection_configuration_set(const struct shell *shell,
			const struct bt_le_conn_param *conn_param,
			const struct bt_conn_le_phy_param *phy,
			const struct bt_conn_le_data_len_param *data_len)
{
	int err;
	struct bt_conn_info info = {0};

	err = bt_conn_get_info(default_conn, &info);
	if (err) {
		shell_error(shell, "Failed to get connection info %d", err);
		return err;
	}

	if (info.role != BT_CONN_ROLE_CENTRAL) {
		shell_error(shell,
		"'run' command shall be executed only on the central board");
	}

	err = bt_conn_le_phy_update(default_conn, phy);
	if (err) {
		shell_error(shell, "PHY update failed: %d\n", err);
		return err;
	}

	shell_print(shell, "PHY update pending");
	err = k_sem_take(&throughput_sem, THROUGHPUT_CONFIG_TIMEOUT);
	if (err) {
		shell_error(shell, "PHY update timeout");
		return err;
	}

	if (info.le.interval != conn_param->interval_max) {
		err = bt_conn_le_param_update(default_conn, conn_param);
		if (err) {
			shell_error(shell,
				    "Connection parameters update failed: %d",
				    err);
			return err;
		}

		shell_print(shell, "Connection parameters update pending");
		err = k_sem_take(&throughput_sem, THROUGHPUT_CONFIG_TIMEOUT);
		if (err) {
			shell_error(shell,
				    "Connection parameters update timeout");
			return err;
		}
	}

	if (info.le.data_len->tx_max_len != data_len->tx_max_len) {
		data_length_req = true;

		err = bt_conn_le_data_len_update(default_conn, data_len);
		if (err) {
			shell_error(shell, "LE data length update failed: %d",
				    err);
			return err;
		}

		shell_print(shell, "LE Data length update pending");
		err = k_sem_take(&throughput_sem, THROUGHPUT_CONFIG_TIMEOUT);
		if (err) {
			shell_error(shell, "LE Data Length update timeout");
			return err;
		}
	}

	if (g_tx_power != 0) {


		    shell_print(shell, "Setting TX power to : %d dBm",
                g_tx_power);

    struct net_buf *buf, *rsp = NULL;
    struct bt_hci_cp_vs_write_tx_power_level *cp;
    struct bt_hci_rp_vs_write_tx_power_level *rp;
    int err;

    buf = bt_hci_cmd_create(BT_HCI_OP_VS_WRITE_TX_POWER_LEVEL,
                            sizeof(*cp));
    if (!buf) {
        shell_error(shell, "No HCI buffer");
        return -ENOMEM;
    }

	err = bt_hci_get_conn_handle(default_conn,
						&default_conn_handle);
	if (err) {
		shell_print(shell,"No connection handle (err %d)", err);
		return err;
	} 

    cp = net_buf_add(buf, sizeof(*cp));
    cp->handle_type    = BT_HCI_VS_LL_HANDLE_TYPE_CONN;
    cp->handle         = sys_cpu_to_le16(default_conn_handle);
    cp->tx_power_level = g_tx_power;

    err = bt_hci_cmd_send_sync(BT_HCI_OP_VS_WRITE_TX_POWER_LEVEL,
                               buf, &rsp);
    if (err) {
        shell_error(shell, "Error setting TX power: %d", err);
        return err;
    }

    rp = (void *)rsp->data;
    shell_print(shell, "Actual TX power: %d dBm",
                rp->selected_tx_power);

    net_buf_unref(rsp);
}

	return 0;
}

int test_run(const struct shell *shell,
	     const struct bt_le_conn_param *conn_param,
	     const struct bt_conn_le_phy_param *phy,
	     const struct bt_conn_le_data_len_param *data_len)
{
	int err;
	uint64_t stamp;
	int64_t delta;
	uint32_t data = 0;
	int64_t  rssi_sum   = 0;
    int      rssi_count = 0;

	/* a dummy data buffer */
	static char dummy[495];

	if (!default_conn) {
		shell_error(shell, "Device is disconnected %s",
			    "Connect to the peer device before running test");
		return -EFAULT;
	}

	if (!test_ready) {
		shell_error(shell, "Device is not ready."
			"Please wait for the service discovery and MTU exchange end");
		return 0;
	}

	shell_print(shell, "\n==== Starting throughput test ====");

	err = connection_configuration_set(shell, conn_param, phy, data_len);
	if (err) {
		return err;
	}

	shell_print(shell, "The test is in progress and will require around %d seconds "
		"to complete.", CONFIG_BT_THROUGHPUT_DURATION / 1000);

	/* Make sure that all BLE procedures are finished. */
	k_sleep(K_MSEC(500));

	/* reset peer metrics */
	err = bt_throughput_write(&throughput, dummy, 1);
	if (err) {
		shell_error(shell, "Reset peer metrics failed.");
		return err;
	}

	/* get cycle stamp */
	stamp = k_uptime_get_32();

	while (true) {
		err = bt_throughput_write(&throughput, dummy, 495);
		if (err) {
			shell_error(shell, "GATT write failed (err %d)", err);
			break;
		}

		{
            int8_t rssi;
            if (read_conn_rssi_val(bt_conn_index(default_conn), &rssi) == 0) {
                rssi_sum   += rssi;
                rssi_count += 1;
            }
        }

		data += 495;
		if (k_uptime_get_32() - stamp > CONFIG_BT_THROUGHPUT_DURATION) {
			break;
		}
	}

	delta = k_uptime_delta(&stamp);

	printk("\nDone\n");
	printk("[local] sent %u bytes (%u KB) in %lld ms at %llu kbps\n",
	       data, data / 1024, delta, ((uint64_t)data * 8 / delta));

	if (rssi_count > 0) {
        int8_t avg_rssi = rssi_sum / rssi_count;
        printk("Average RSSI: %d dBm over %d samples\n",
               avg_rssi, rssi_count);
    } else {
        printk("No RSSI samples collected\n");
    }

	/* read back char from peer */
	err = bt_throughput_read(&throughput);
	if (err) {
		shell_error(shell, "GATT read failed (err %d)", err);
		return err;
	}

	k_sem_take(&throughput_sem, THROUGHPUT_CONFIG_TIMEOUT);

	instruction_print();

	return 0;
}

BT_CONN_CB_DEFINE(conn_callbacks) = {
	.connected = connected,
	.disconnected = disconnected,
	.le_param_req = le_param_req,
	.le_param_updated = le_param_updated,
	.le_phy_updated = le_phy_updated,
	.le_data_len_updated = le_data_length_updated,
	.security_changed = security_changed
};

int main(void)
{
	int err;

	printk("Starting Bluetooth Throughput example\n");

	err = bt_enable(NULL);
	if (err) {
		printk("Bluetooth init failed (err %d)\n", err);
		return 0;
	}

	printk("Bluetooth initialized\n");

	scan_init();

	err = bt_throughput_init(&throughput, &throughput_cb);
	if (err) {
		printk("Throughput service initialization failed.\n");
		return 0;
	}

	printk("\n");

	if (IS_ENABLED(CONFIG_SOC_SERIES_NRF54HX) || IS_ENABLED(CONFIG_SOC_SERIES_NRF54LX)) {
		printk("Press button 0 or type \"central\" on the central board.\n");
		printk("Press button 1 or type \"peripheral\" on the peripheral board.\n");
	} else {
		printk("Press button 1 or type \"central\" on the central board.\n");
		printk("Press button 2 or type \"peripheral\" on the peripheral board.\n");
	}

	buttons_init();

	return 0;
}

PS: Max tx-power on nRF5340 is 3 dbm.