Desired TX power is not consistent with exact TXP when using nRF21540

[Ziyao Zhou]

Hi

I am using HCI Power Control sample to dynamically control TX power. I found that the TX side's connection RSSI and RX side's are diferent, at some point it even has 20 db difference!  Which one is the correct one?

My TX code:

/* main.c - Application main entry point */

/*
 * Copyright (c) 2019 Andrei Stoica
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/types.h>
#include <stddef.h>
#include <zephyr/sys/printk.h>
#include <zephyr/sys/util.h>
#include <zephyr/sys/byteorder.h>

#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>
//#include <zephyr/bluetooth/services/hrs.h>
#include <bluetooth/services/nus.h>

static struct bt_conn *default_conn;
static uint16_t default_conn_handle;

#define DEVICE_NAME         CONFIG_BT_DEVICE_NAME
#define DEVICE_NAME_LEN     (sizeof(DEVICE_NAME) - 1)

/* 虚拟命令字符串 */
static const char cmd_str[] = "123456789";


/* Advertising 数据 */
static const struct bt_data ad[] = {
    BT_DATA_BYTES(BT_DATA_FLAGS, (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
    BT_DATA(BT_DATA_NAME_COMPLETE, DEVICE_NAME, DEVICE_NAME_LEN),
};

static const struct bt_data sd[] = {
    BT_DATA_BYTES(BT_DATA_UUID128_ALL, BT_UUID_NUS_VAL),
};






#define DEVICE_BEACON_TXPOWER_NUM  8

static struct k_thread pwr_thread_data;
static K_THREAD_STACK_DEFINE(pwr_thread_stack, 512);

static const int8_t txpower[DEVICE_BEACON_TXPOWER_NUM] = {4, 0, -3, -8,
							  -15, -18, -23, -30};
static const struct bt_le_adv_param *param =
	BT_LE_ADV_PARAM(BT_LE_ADV_OPT_CONNECTABLE | BT_LE_ADV_OPT_ONE_TIME, 0x0020, 0x0020, NULL);





	/* NUS 收到数据回调 */
static void bt_receive_cb(struct bt_conn *conn, const uint8_t *const data, uint16_t len)
{
    printk("NUS Received: %.*s\n", len, data);
}

/* NUS 回调结构 */
static struct bt_nus_cb nus_cb = {
    .received = bt_receive_cb,
};



/* 定时发送函数 */
static void nus_notify(void)
{
    if (default_conn) {
        int err = bt_nus_send(default_conn, cmd_str, sizeof(cmd_str) - 1);
        if (err == -ENOMEM) {
            printk("Failed to send NUS data: Out of memory (err %d)\n", err);
        } else if (err) {
            printk("Failed to send NUS data (err %d)\n", err);
        } else {
            printk("NUS Sent: %s\n", cmd_str);
        }
    } else {
        printk("No active connection, skipping send\n");
    }
}



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) {
		printk("Read RSSI err: %d\n", err);
		return;
	}

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

	net_buf_unref(rsp);
}


static void set_tx_power(uint8_t handle_type, uint16_t handle, int8_t tx_pwr_lvl)
{
	struct bt_hci_cp_vs_write_tx_power_level *cp;
	struct bt_hci_rp_vs_write_tx_power_level *rp;
	struct net_buf *buf, *rsp = NULL;
	int err;

	buf = bt_hci_cmd_create(BT_HCI_OP_VS_WRITE_TX_POWER_LEVEL,
				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);
	cp->handle_type = handle_type;
	cp->tx_power_level = tx_pwr_lvl;

	err = bt_hci_cmd_send_sync(BT_HCI_OP_VS_WRITE_TX_POWER_LEVEL,
				   buf, &rsp);
	if (err) {
		printk("Set Tx power err: %d\n", err);
		return;
	}

	rp = (void *)rsp->data;
	printk("Actual Tx Power: %d\n", rp->selected_tx_power);

	net_buf_unref(rsp);
}

static void get_tx_power(uint8_t handle_type, uint16_t handle, int8_t *tx_pwr_lvl)
{
	struct bt_hci_cp_vs_read_tx_power_level *cp;
	struct bt_hci_rp_vs_read_tx_power_level *rp;
	struct net_buf *buf, *rsp = NULL;
	int err;

	*tx_pwr_lvl = 0xFF;
	buf = bt_hci_cmd_create(BT_HCI_OP_VS_READ_TX_POWER_LEVEL,
				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);
	cp->handle_type = handle_type;

	err = bt_hci_cmd_send_sync(BT_HCI_OP_VS_READ_TX_POWER_LEVEL,
				   buf, &rsp);
	if (err) {
		printk("Read Tx power err: %d\n", err);
		return;
	}

	rp = (void *)rsp->data;
	*tx_pwr_lvl = rp->tx_power_level;

	net_buf_unref(rsp);
}

static void connected(struct bt_conn *conn, uint8_t err)
{
	char addr[BT_ADDR_LE_STR_LEN];
	int8_t txp;
	int ret;

	if (err) {
		printk("Connection failed, err 0x%02x %s\n", err, bt_hci_err_to_str(err));
	} else {
		default_conn = bt_conn_ref(conn);
		ret = bt_hci_get_conn_handle(default_conn,
					     &default_conn_handle);
		if (ret) {
			printk("No connection handle (err %d)\n", ret);
		} else {
			/* Send first at the default selected power */
			bt_addr_le_to_str(bt_conn_get_dst(conn),
							  addr, sizeof(addr));
			printk("Connected via connection (%d) at %s\n",
			       default_conn_handle, addr);
			get_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_CONN,
				     default_conn_handle, &txp);
			printk("Connection (%d) - Initial Tx Power = %d\n",
			       default_conn_handle, txp);

			set_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_CONN,
				     default_conn_handle,
				     BT_HCI_VS_LL_TX_POWER_LEVEL_NO_PREF);
			get_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_CONN,
				     default_conn_handle, &txp);
			printk("Connection (%d) - Tx Power = %d\n",
			       default_conn_handle, txp);
		}
	}
}

static void disconnected(struct bt_conn *conn, uint8_t reason)
{
	printk("Disconnected, reason 0x%02x %s\n", reason, bt_hci_err_to_str(reason));

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

BT_CONN_CB_DEFINE(conn_callbacks) = {
	.connected = connected,
	.disconnected = disconnected,
};

static void bt_ready(int err)
{
	if (err) {
		printk("Bluetooth init failed (err %d)\n", err);
		return;
	}

	printk("Bluetooth initialized\n");

	/* Start advertising */
	err = bt_le_adv_start(param, ad, ARRAY_SIZE(ad),
			      sd, ARRAY_SIZE(sd));
	if (err) {
		printk("Advertising failed to start (err %d)\n", err);
		return;
	}

	printk("Dynamic Tx power Beacon started\n");
}


void modulate_tx_power(void *p1, void *p2, void *p3)
{
	int8_t txp_get = 0;
	uint8_t idx = 0;

	while (1) {
		if (!default_conn) {
			printk("Set Tx power level to %d\n", txpower[idx]);
			set_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_ADV,
				     0, txpower[idx]);

			k_sleep(K_SECONDS(5));

			printk("Get Tx power level -> ");
			get_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_ADV,
				     0, &txp_get);
			printk("TXP = %d\n", txp_get);

			idx = (idx+1) % DEVICE_BEACON_TXPOWER_NUM;
		} else {
			int8_t rssi = 0xFF;
			int8_t txp_adaptive;

			idx = 0;

			read_conn_rssi(default_conn_handle, &rssi);
			printk("Connected (%d) - RSSI = %d\n",
			       default_conn_handle, rssi);
			if (rssi > -70) {
				txp_adaptive = -20;
			} else if (rssi > -90) {
				txp_adaptive = -12;
			} else {
				txp_adaptive = -4;
			}
			printk("Adaptive Tx power selected = %d\n",
			       txp_adaptive);
			set_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_CONN,
				     default_conn_handle, txp_adaptive);
			get_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_CONN,
				     default_conn_handle, &txp_get);
			printk("Connection (%d) TXP = %d\n",
			       default_conn_handle, txp_get);

			k_sleep(K_SECONDS(1));
		}
	}
}

int main(void)
{
	int8_t txp_get = 0xFF;
	int err;

	default_conn = NULL;
	printk("Starting Dynamic Tx Power Beacon Demo\n");

	/* Initialize the Bluetooth Subsystem */
	err = bt_enable(bt_ready);
	if (err) {
		printk("Bluetooth init failed (err %d)\n", err);
	}

	err = bt_nus_init(&nus_cb);
    if (err) {
        printk("Failed to initialize NUS (err %d)\n", err);
        return err;
    }

	printk("Get Tx power level ->");
	get_tx_power(BT_HCI_VS_LL_HANDLE_TYPE_ADV, 0, &txp_get);
	printk("-> default TXP = %d\n", txp_get);

	/* Wait for 5 seconds to give a chance users/testers
	 * to check that default Tx power is indeed the one
	 * selected in Kconfig.
	 */
	k_sleep(K_SECONDS(5));

	k_thread_create(&pwr_thread_data, pwr_thread_stack,
			K_THREAD_STACK_SIZEOF(pwr_thread_stack),
			modulate_tx_power, NULL, NULL, NULL,
			K_PRIO_COOP(10),
			0, K_NO_WAIT);
	k_thread_name_set(&pwr_thread_data, "DYN TX");

	while (1) {
		// hrs_notify();
		nus_notify();
		k_sleep(K_SECONDS(1));

	}
	return 0;
}

My RX code：

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

/** @file
 *  @brief Nordic UART Service Client sample
 */

#include <errno.h>
#include <zephyr/kernel.h>
#include <zephyr/device.h>
#include <zephyr/devicetree.h>
#include <zephyr/sys/byteorder.h>
#include <zephyr/sys/printk.h>

#include <zephyr/bluetooth/bluetooth.h>
#include <zephyr/bluetooth/hci.h>
#include <zephyr/bluetooth/conn.h>
#include <zephyr/bluetooth/uuid.h>
#include <zephyr/bluetooth/gatt.h>

#include <bluetooth/services/nus.h>
#include <bluetooth/services/nus_client.h>
#include <bluetooth/gatt_dm.h>
#include <bluetooth/scan.h>

#include <zephyr/settings/settings.h>

#include <zephyr/drivers/uart.h>

#include <zephyr/logging/log.h>

#include <zephyr/bluetooth/hci.h>


#define LOG_MODULE_NAME central_uart
LOG_MODULE_REGISTER(LOG_MODULE_NAME);

/* UART payload buffer element size. */
#define UART_BUF_SIZE 45

#define KEY_PASSKEY_ACCEPT DK_BTN1_MSK
#define KEY_PASSKEY_REJECT DK_BTN2_MSK

#define NUS_WRITE_TIMEOUT K_MSEC(150)
#define UART_WAIT_FOR_BUF_DELAY K_MSEC(50)
#define UART_RX_TIMEOUT 50000 /* Wait for RX complete event time in microseconds. */

static const struct device *uart = DEVICE_DT_GET(DT_CHOSEN(nordic_nus_uart));
static struct k_work_delayable uart_work;

K_SEM_DEFINE(nus_write_sem, 0, 1);

struct uart_data_t {
	void *fifo_reserved;
	uint8_t  data[UART_BUF_SIZE];
	uint16_t len;
};

static K_FIFO_DEFINE(fifo_uart_tx_data);
static K_FIFO_DEFINE(fifo_uart_rx_data);

static struct bt_conn *default_conn;
static struct bt_nus_client nus_client;







static char last_received_data[UART_BUF_SIZE] = {0};
static uint16_t last_received_data_len = 0;
static struct k_work_delayable rssi_work;

// static void rssi_work_handler(struct k_work *work)
// {
//     struct bt_conn_info info;
//     struct net_buf *buf = NULL, *rsp = NULL;
//     struct bt_hci_cp_read_rssi *cp;
//     struct bt_hci_rp_read_rssi *rp;
//     int err;
	
// 	if (default_conn) {
//         struct bt_conn_info info;
//         int err;

//         // 获取当前连接信息
//         err = bt_conn_get_info(default_conn, &info);
//         if (err) {
//             LOG_ERR("Failed to get connection info (err %d)", err);
//             return;
//         }

//         // 创建HCI命令缓冲区以读取RSSI
//         struct net_buf *buf = bt_hci_cmd_create(BT_HCI_OP_READ_RSSI, sizeof(uint16_t));
//         if (!buf) {
//             LOG_ERR("Failed to create HCI command buffer");
//             return;
//         }

//         // 填充HCI命令
//         struct bt_hci_cp_read_rssi *cp = net_buf_add(buf, sizeof(*cp));
//         cp->handle = sys_cpu_to_le16(info.id);

//         // 发送命令并解析响应
//         struct net_buf *rsp;
//         err = bt_hci_cmd_send_sync(BT_HCI_OP_READ_RSSI, buf, &rsp);
//         if (err) {
//             LOG_ERR("Failed to read RSSI (err %d)", err);
//             return;
//         }

//         struct bt_hci_rp_read_rssi *rp = (void *)rsp->data;
//         LOG_INF("RSSI: %d dBm", rp->rssi);
// 		LOG_INF("Data received: %.*s", last_received_data_len, last_received_data);

//         net_buf_unref(rsp);
//     }

//     // 调度下一次任务
//     k_work_reschedule(&rssi_work, K_SECONDS(1));  // 每秒读取一次RSSI
// }
static void rssi_work_handler(struct k_work *work)
{
    struct bt_conn_info info;
    struct net_buf *buf = NULL, *rsp = NULL;
    struct bt_hci_cp_read_rssi *cp;
    struct bt_hci_rp_read_rssi *rp;
    int err;

    if (!default_conn) {
        LOG_ERR("No default connection available");
        goto schedule;
    }

    /* 获取当前连接信息 */
    err = bt_conn_get_info(default_conn, &info);
    if (err) {
        LOG_ERR("Failed to get connection info (err %d)", err);
        goto schedule;
    }

    /* 创建 HCI 命令缓冲区以读取 RSSI */
    buf = bt_hci_cmd_create(BT_HCI_OP_READ_RSSI, sizeof(*cp));
    if (!buf) {
        LOG_ERR("Unable to allocate HCI command buffer");
        goto schedule;
    }

    /* 填充 HCI 命令数据（使用连接标识 info.id 作为句柄） */
    cp = net_buf_add(buf, sizeof(*cp));
    cp->handle = sys_cpu_to_le16(info.id);

    /* 发送 HCI 命令并等待同步响应 */
    err = bt_hci_cmd_send_sync(BT_HCI_OP_READ_RSSI, buf, &rsp);
    if (err) {
        LOG_ERR("Read RSSI error: %d", err);
        goto schedule;
    }

    /* 解析并打印 RSSI 数据 */
    rp = (void *)rsp->data;
    LOG_INF("RSSI: %d dBm", rp->rssi);
	LOG_INF("Data received: %.*s", last_received_data_len, last_received_data);

    net_buf_unref(rsp);

schedule:
    /* 调度下一次任务：每秒读取一次 RSSI */
    k_work_reschedule(&rssi_work, K_SECONDS(1));
}










static void ble_data_sent(struct bt_nus_client *nus, uint8_t err,
					const uint8_t *const data, uint16_t len)
{
	ARG_UNUSED(nus);
	ARG_UNUSED(data);
	ARG_UNUSED(len);

	k_sem_give(&nus_write_sem);

	if (err) {
		LOG_WRN("ATT error code: 0x%02X", err);
	}
}

// static uint8_t ble_data_received(struct bt_nus_client *nus,
// 						const uint8_t *data, uint16_t len)
// {
// 	ARG_UNUSED(nus);

// 	int err;

// 	for (uint16_t pos = 0; pos != len;) {
// 		struct uart_data_t *tx = k_malloc(sizeof(*tx));

// 		if (!tx) {
// 			LOG_WRN("Not able to allocate UART send data buffer");
// 			return BT_GATT_ITER_CONTINUE;
// 		}

// 		/* Keep the last byte of TX buffer for potential LF char. */
// 		size_t tx_data_size = sizeof(tx->data) - 1;

// 		if ((len - pos) > tx_data_size) {
// 			tx->len = tx_data_size;
// 		} else {
// 			tx->len = (len - pos);
// 		}

// 		memcpy(tx->data, &data[pos], tx->len);

// 		pos += tx->len;

// 		/* Append the LF character when the CR character triggered
// 		 * transmission from the peer.
// 		 */
// 		if ((pos == len) && (data[len - 1] == '\r')) {
// 			tx->data[tx->len] = '\n';
// 			tx->len++;
// 		}

// 		err = uart_tx(uart, tx->data, tx->len, SYS_FOREVER_MS);
// 		if (err) {
// 			k_fifo_put(&fifo_uart_tx_data, tx);
// 		}
// 	}

// 	return BT_GATT_ITER_CONTINUE;
// }






static uint8_t ble_data_received(struct bt_nus_client *nus,
                                 const uint8_t *data, uint16_t len)
{
    ARG_UNUSED(nus);

    // 保存接收到的数据
    memset(last_received_data, 0, sizeof(last_received_data));
    last_received_data_len = len < UART_BUF_SIZE ? len : UART_BUF_SIZE - 1;
    memcpy(last_received_data, data, last_received_data_len);

    //LOG_INF("Data received: %.*s", last_received_data_len, last_received_data);

    return BT_GATT_ITER_CONTINUE;
}









static void uart_cb(const struct device *dev, struct uart_event *evt, void *user_data)
{
	ARG_UNUSED(dev);

	static size_t aborted_len;
	struct uart_data_t *buf;
	static uint8_t *aborted_buf;
	static bool disable_req;

	switch (evt->type) {
	case UART_TX_DONE:
		LOG_DBG("UART_TX_DONE");
		if ((evt->data.tx.len == 0) ||
		    (!evt->data.tx.buf)) {
			return;
		}

		if (aborted_buf) {
			buf = CONTAINER_OF(aborted_buf, struct uart_data_t,
					   data[0]);
			aborted_buf = NULL;
			aborted_len = 0;
		} else {
			buf = CONTAINER_OF(evt->data.tx.buf,
					   struct uart_data_t,
					   data[0]);
		}

		k_free(buf);

		buf = k_fifo_get(&fifo_uart_tx_data, K_NO_WAIT);
		if (!buf) {
			return;
		}

		if (uart_tx(uart, buf->data, buf->len, SYS_FOREVER_MS)) {
			LOG_WRN("Failed to send data over UART");
		}

		break;

	case UART_RX_RDY:
		LOG_DBG("UART_RX_RDY");
		buf = CONTAINER_OF(evt->data.rx.buf, struct uart_data_t, data[0]);
		buf->len += evt->data.rx.len;

		if (disable_req) {
			return;
		}

		if ((evt->data.rx.buf[buf->len - 1] == '\n') ||
		    (evt->data.rx.buf[buf->len - 1] == '\r')) {
			disable_req = true;
			uart_rx_disable(uart);
		}

		break;

	case UART_RX_DISABLED:
		LOG_DBG("UART_RX_DISABLED");
		disable_req = false;

		buf = k_malloc(sizeof(*buf));
		if (buf) {
			buf->len = 0;
		} else {
			LOG_WRN("Not able to allocate UART receive buffer");
			k_work_reschedule(&uart_work, UART_WAIT_FOR_BUF_DELAY);
			return;
		}

		uart_rx_enable(uart, buf->data, sizeof(buf->data),
			       UART_RX_TIMEOUT);

		break;

	case UART_RX_BUF_REQUEST:
		LOG_DBG("UART_RX_BUF_REQUEST");
		buf = k_malloc(sizeof(*buf));
		if (buf) {
			buf->len = 0;
			uart_rx_buf_rsp(uart, buf->data, sizeof(buf->data));
		} else {
			LOG_WRN("Not able to allocate UART receive buffer");
		}

		break;

	case UART_RX_BUF_RELEASED:
		LOG_DBG("UART_RX_BUF_RELEASED");
		buf = CONTAINER_OF(evt->data.rx_buf.buf, struct uart_data_t,
				   data[0]);

		if (buf->len > 0) {
			k_fifo_put(&fifo_uart_rx_data, buf);
		} else {
			k_free(buf);
		}

		break;

	case UART_TX_ABORTED:
		LOG_DBG("UART_TX_ABORTED");
		if (!aborted_buf) {
			aborted_buf = (uint8_t *)evt->data.tx.buf;
		}

		aborted_len += evt->data.tx.len;
		buf = CONTAINER_OF(aborted_buf, struct uart_data_t,
				   data[0]);

		uart_tx(uart, &buf->data[aborted_len],
			buf->len - aborted_len, SYS_FOREVER_MS);

		break;

	default:
		break;
	}
}

static void uart_work_handler(struct k_work *item)
{
	struct uart_data_t *buf;

	buf = k_malloc(sizeof(*buf));
	if (buf) {
		buf->len = 0;
	} else {
		LOG_WRN("Not able to allocate UART receive buffer");
		k_work_reschedule(&uart_work, UART_WAIT_FOR_BUF_DELAY);
		return;
	}

	uart_rx_enable(uart, buf->data, sizeof(buf->data), UART_RX_TIMEOUT);
}

static int uart_init(void)
{
	int err;
	struct uart_data_t *rx;

	if (!device_is_ready(uart)) {
		LOG_ERR("UART device not ready");
		return -ENODEV;
	}

	rx = k_malloc(sizeof(*rx));
	if (rx) {
		rx->len = 0;
	} else {
		return -ENOMEM;
	}

	k_work_init_delayable(&uart_work, uart_work_handler);

	err = uart_callback_set(uart, uart_cb, NULL);
	if (err) {
		return err;
	}

	return uart_rx_enable(uart, rx->data, sizeof(rx->data),
			      UART_RX_TIMEOUT);
}

static void discovery_complete(struct bt_gatt_dm *dm,
			       void *context)
{
	struct bt_nus_client *nus = context;
	LOG_INF("Service discovery completed");

	bt_gatt_dm_data_print(dm);

	bt_nus_handles_assign(dm, nus);
	bt_nus_subscribe_receive(nus);

	bt_gatt_dm_data_release(dm);
}

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

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

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

static void gatt_discover(struct bt_conn *conn)
{
	int err;

	if (conn != default_conn) {
		return;
	}

	err = bt_gatt_dm_start(conn,
			       BT_UUID_NUS_SERVICE,
			       &discovery_cb,
			       &nus_client);
	if (err) {
		LOG_ERR("could not start the discovery procedure, error "
			"code: %d", err);
	}
}

static void exchange_func(struct bt_conn *conn, uint8_t err, struct bt_gatt_exchange_params *params)
{
	if (!err) {
		LOG_INF("MTU exchange done");
	} else {
		LOG_WRN("MTU exchange failed (err %" PRIu8 ")", err);
	}
}

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

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

	if (conn_err) {
		LOG_INF("Failed to connect to %s, 0x%02x %s", addr, conn_err,
			bt_hci_err_to_str(conn_err));

		if (default_conn == conn) {
			bt_conn_unref(default_conn);
			default_conn = NULL;

			err = bt_scan_start(BT_SCAN_TYPE_SCAN_ACTIVE);
			if (err) {
				LOG_ERR("Scanning failed to start (err %d)",
					err);
			}
		}

		return;
	}

	LOG_INF("Connected: %s", addr);

	static struct bt_gatt_exchange_params exchange_params;

	exchange_params.func = exchange_func;
	err = bt_gatt_exchange_mtu(conn, &exchange_params);
	if (err) {
		LOG_WRN("MTU exchange failed (err %d)", err);
	}

	err = bt_conn_set_security(conn, BT_SECURITY_L2);
	if (err) {
		LOG_WRN("Failed to set security: %d", err);

		gatt_discover(conn);
	}

	err = bt_scan_stop();
	if ((!err) && (err != -EALREADY)) {
		LOG_ERR("Stop LE scan failed (err %d)", err);
	}

	// 启动任务
    k_work_schedule(&rssi_work, K_NO_WAIT);
}

static void disconnected(struct bt_conn *conn, uint8_t reason)
{
	k_work_cancel_delayable(&rssi_work);  // 取消RSSI任务

	char addr[BT_ADDR_LE_STR_LEN];
	int err;

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

	LOG_INF("Disconnected: %s, reason 0x%02x %s", addr, reason, bt_hci_err_to_str(reason));
	


	if (default_conn != conn) {
		return;
	}

	bt_conn_unref(default_conn);
	default_conn = NULL;



	err = bt_scan_start(BT_SCAN_TYPE_SCAN_ACTIVE);
	if (err) {
		LOG_ERR("Scanning failed to start (err %d)",
			err);
	}

}

static void security_changed(struct bt_conn *conn, bt_security_t level,
			     enum bt_security_err err)
{
	char addr[BT_ADDR_LE_STR_LEN];

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

	if (!err) {
		LOG_INF("Security changed: %s level %u", addr, level);
	} else {
		LOG_WRN("Security failed: %s level %u err %d %s", addr, level, err,
			bt_security_err_to_str(err));
			
	}

	gatt_discover(conn);
}

BT_CONN_CB_DEFINE(conn_callbacks) = {
	.connected = connected,
	.disconnected = disconnected,
	.security_changed = security_changed
};

static 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));

	LOG_INF("Filters matched. Address: %s connectable: %d",
		addr, connectable);

		
}

static void scan_connecting_error(struct bt_scan_device_info *device_info)
{
	LOG_WRN("Connecting failed");
}

static void scan_connecting(struct bt_scan_device_info *device_info,
			    struct bt_conn *conn)
{
	default_conn = bt_conn_ref(conn);
}

static int nus_client_init(void)
{
	int err;
	struct bt_nus_client_init_param init = {
		.cb = {
			.received = ble_data_received,
			.sent = ble_data_sent,
		}
	};

	err = bt_nus_client_init(&nus_client, &init);
	if (err) {
		LOG_ERR("NUS Client initialization failed (err %d)", err);
		return err;
	}

	LOG_INF("NUS Client module initialized");
	return err;
}

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

static int scan_init(void)
{
	int err;
	struct bt_scan_init_param scan_init = {
		.connect_if_match = 1,
	};

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

	err = bt_scan_filter_add(BT_SCAN_FILTER_TYPE_UUID, BT_UUID_NUS_SERVICE);
	if (err) {
		LOG_ERR("Scanning filters cannot be set (err %d)", err);
		return err;
	}

	err = bt_scan_filter_add(BT_SCAN_FILTER_TYPE_NAME, "Dynamic test beacon"); // 替换为目标设备的名称
    if (err) {
        LOG_ERR("Failed to set name filter (err %d)", err);
        return err;
    }

	err = bt_scan_filter_enable(BT_SCAN_UUID_FILTER|BT_SCAN_NAME_FILTER, false);
	if (err) {
		LOG_ERR("Filters cannot be turned on (err %d)", err);
		return err;
	}

	LOG_INF("Scan module initialized");
	return err;
}


static void auth_cancel(struct bt_conn *conn)
{
	char addr[BT_ADDR_LE_STR_LEN];

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

	LOG_INF("Pairing cancelled: %s", addr);
}


static void pairing_complete(struct bt_conn *conn, bool bonded)
{
	char addr[BT_ADDR_LE_STR_LEN];

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

	LOG_INF("Pairing completed: %s, bonded: %d", addr, bonded);
}


static void pairing_failed(struct bt_conn *conn, enum bt_security_err reason)
{
	char addr[BT_ADDR_LE_STR_LEN];

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

	LOG_WRN("Pairing failed conn: %s, reason %d %s", addr, reason,
		bt_security_err_to_str(reason));
}

static struct bt_conn_auth_cb conn_auth_callbacks = {
	.cancel = auth_cancel,
};

static struct bt_conn_auth_info_cb conn_auth_info_callbacks = {
	.pairing_complete = pairing_complete,
	.pairing_failed = pairing_failed
};

int main(void)
{
	int err;

	 k_work_init_delayable(&rssi_work, rssi_work_handler);

	err = bt_conn_auth_cb_register(&conn_auth_callbacks);
	if (err) {
		LOG_ERR("Failed to register authorization callbacks.");
		return 0;
	}

	err = bt_conn_auth_info_cb_register(&conn_auth_info_callbacks);
	if (err) {
		printk("Failed to register authorization info callbacks.\n");
		return 0;
	}

	err = bt_enable(NULL);
	if (err) {
		LOG_ERR("Bluetooth init failed (err %d)", err);
		return 0;
	}
	LOG_INF("Bluetooth initialized");



	if (IS_ENABLED(CONFIG_SETTINGS)) {
		settings_load();
	}

	err = uart_init();
	if (err != 0) {
		LOG_ERR("uart_init failed (err %d)", err);
		return 0;
	}

	err = scan_init();
	if (err != 0) {
		LOG_ERR("scan_init failed (err %d)", err);
		return 0;
	}

	err = nus_client_init();
	if (err != 0) {
		LOG_ERR("nus_client_init failed (err %d)", err);
		return 0;
	}

	printk("Starting Bluetooth Central UART example\n");

	err = bt_scan_start(BT_SCAN_TYPE_SCAN_ACTIVE);
	if (err) {
		LOG_ERR("Scanning failed to start (err %d)", err);
		return 0;
	}

	LOG_INF("Scanning successfully started");

	struct uart_data_t nus_data = {
		.len = 0,
	};

	for (;;) {
		/* Wait indefinitely for data to be sent over Bluetooth */
		struct uart_data_t *buf = k_fifo_get(&fifo_uart_rx_data,
						     K_FOREVER);

		int plen = MIN(sizeof(nus_data.data) - nus_data.len, buf->len);
		int loc = 0;

		while (plen > 0) {
			memcpy(&nus_data.data[nus_data.len], &buf->data[loc], plen);
			nus_data.len += plen;
			loc += plen;
			if (nus_data.len >= sizeof(nus_data.data) ||
			   (nus_data.data[nus_data.len - 1] == '\n') ||
			   (nus_data.data[nus_data.len - 1] == '\r')) {
				err = bt_nus_client_send(&nus_client, nus_data.data, nus_data.len);
				if (err) {
					LOG_WRN("Failed to send data over BLE connection"
						"(err %d)", err);
				}

				err = k_sem_take(&nus_write_sem, NUS_WRITE_TIMEOUT);
				if (err) {
					LOG_WRN("NUS send timeout");
				}

				nus_data.len = 0;
			}

			plen = MIN(sizeof(nus_data.data), buf->len - loc);
		}

		k_free(buf);
	}
}

Thank you so much for your time!

[Ziyao Zhou]

Another problem is that the granularity of adjustment does not seem to be very high. I used my method to select a new TX power each time, but it could not be configured successfully. It seems that the system can only work at a few discrete values. （I am using nrf21540 EK and have add the related stuff）

00> Adaptive Tx power selected = -13
00> Actual Tx Power: -20

00> Adaptive Tx power selected = -14
00> Actual Tx Power: -20

00> Adaptive Tx power selected = 7
00> Actual Tx Power: 4

00> Adaptive Tx power selected = 3
00> Actual Tx Power: 0

00> Adaptive Tx power selected = 1
00> Actual Tx Power: 0

00> Adaptive Tx power selected = -5
00> Actual Tx Power: -20

Thank you so much

[Einar Thorsrud]

Hi,

How are you building the project? If you are building for the nRF21540 FEM, the output power is configurable with high resolution. However, when building withotu the FEM, the output power is limited to the steps that are supported in HW (see TXPOWER in the product specification), and if you specify an unsupported value, the closest lower output power is used.

Regarding the measured RSSI that depend on many factors, one is real factors and only give a ball park number. The RSSI measurment itself is specified to be +-1 2 dBm, but there are other factors such as antenna, sampling time, perhaps the devices are not transmitting with the same power, etc. 

[Einar Thorsrud]

Hi,

Ziyao Zhou said:

Hi, thank you for the information. Does that mean TX power can only be tuned with these numbers = {20, 10, 4, 0, -3, -8, + -15, -18, -23, -30}？

No, these are just the numbers used in the sample (with my modification ading two more with higher output).

The Tx power you read back will not be exactly what you set if the combination of FEM gain and nRF52833 Tx power does not add up to what you requested (see this post).

[Ziyao Zhou]

Thank you for your information! My problem is when I request Tx power lower than - 10, the exact Tx to be set will always be -30, I cannot go lower than that

[Einar Thorsrud]

Hi,

From what I understand the get_tx_power() function may not represent the actuall configuation when using the nRF21540 FEM with dynamic power control. Have you measured the actual Tx power out of the FEM? There you should see values that are closer to what you configure.

[Ziyao Zhou]

Hi,

I will test the Txpower when I get my power meter : ) will let you know in the future, Thank you so much

[Ziyao Zhou]

Hi

My power meter is still on the way. However, I have done a test regarding the desired TXP and exact TXP getting from the software.

I have already use your config, enabled the power model to have a precise gain control. Is this the expected result when using the nRF21540?

By the way, I noticed that nRF54L15 is not compatible with nRF21540. Does that mean it is only compatible with the unlisted nRF2220 RF？