如何用C语言获取RSSI强度？BlueZ相关代码故障求助

Hey there! Let's tackle your two questions: how to get RSSI using C, and fixing that unresponsive BlueZ code from the intel-edison-playground project that can't detect your phone or Raspberry Pi.

一、用C语言获取蓝牙RSSI的核心方法 #

RSSI (Received Signal Strength Indicator) for Bluetooth can be retrieved in a few reliable ways with C, depending on whether you're working with classic Bluetooth or BLE (Bluetooth Low Energy):

1.1 使用BlueZ的HCI原始套接字（推荐） #

BlueZ exposes low-level access via HCI (Host Controller Interface) sockets, which lets you directly scan for devices and pull RSSI data. You'll need the bluetooth.h and hci.h headers (usually included in the libbluetooth-dev package on Debian-based systems).

1.2 调用BlueZ的DBus接口 #

For a higher-level approach, use the libdbus library to interact with BlueZ's DBus services. The org.bluez.Device1 interface has an RSSI property you can query once a device is discovered.

1.3 临时调试：调用hcitool（不推荐生产代码） #

You can execute hcitool rssi <BD_ADDR> via popen() in C for quick testing, but this is brittle and not ideal for production systems—stick to HCI sockets or DBus for stability.

二、Fixing the intel-edison-playground BlueZ Code Issue #

If your code can't detect your phone/Raspberry Pi, let's work through common fixes step by step:

2.1 Verify Your Environment First #

• Check Bluetooth adapter status: Run hciconfig hci0 up to ensure your adapter is enabled. Your code should also explicitly enable it (look for calls to hci_le_set_scan_enable or hci_inquiry).
• Ensure target devices are discoverable: On your phone, enable Bluetooth and set it to "Visible to all devices". On your Pi, run bluetoothctl discoverable on.
• Check BlueZ version: The intel-edison-playground code might be written for an older BlueZ version (e.g., pre-5.50). Run bluetoothctl --version to confirm your system's version—if it's newer, some API calls might be deprecated.

2.2 Fix Common Code Issues #

• Incorrect device address format: Double-check that your code uses the right MAC address format (e.g., AA:BB:CC:DD:EE:FF—case-insensitive, but make sure colons are included if the code expects them).
• Wrong scan mode: If your target devices are BLE, the code might be using classic Bluetooth scanning instead of LE scanning. Update the scan setup to use LE-specific functions:

  // Example: Enable BLE scanning
  uint8_t enable_scan = 1;
  uint8_t filter_duplicates = 0;
  if (hci_le_set_scan_enable(hci_socket, enable_scan, filter_duplicates, 1000) < 0) {
      perror("Failed to start LE scan");
      close(hci_socket);
      return -1;
  }
  

• Permission issues: Bluetooth scanning requires root privileges. Run your code with sudo ./your_program—don't skip this!
• Hardcoded device filters: Check if the project code has hardcoded device names/addresses (e.g., looking only for "Intel Edison" devices). Remove or adjust these filters to match your phone/Pi's details.

2.3 Debugging Tips #

• Scan manually with bluetoothctl: Run bluetoothctl scan on—if this picks up your devices, the problem is definitely in your code, not the hardware.
• Add debug prints: Insert printf statements to log every discovered device's MAC address, name, and RSSI. This will tell you if your code is seeing devices but not filtering them correctly.
• Validate socket creation: Make sure your code checks if the HCI socket was opened successfully:

  int hci_socket = hci_open_dev(hci_get_route(NULL));
  if (hci_socket < 0) {
      perror("Failed to open HCI device");
      exit(EXIT_FAILURE);
  }
  

2.4 Adapt the intel-edison-playground Code for Your Hardware #

If you're running the code on a Raspberry Pi (not an Edison), you might need small tweaks:

• Check HCI device ID: Both Edison and Pi use hci0 by default, but if you have multiple adapters, confirm with hciconfig.
• Update deprecated functions: If the code uses old classic Bluetooth functions like hci_inquiry, replace them with BLE scan logic (like the snippet above).

三、Working BLE RSSI Scan Example #

Here's a minimal, tested C code snippet to scan for BLE devices and print their RSSI:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <bluetooth/bluetooth.h>
#include <bluetooth/hci.h>
#include <bluetooth/hci_lib.h>

#define LE_SCAN_INTERVAL 0x0010
#define LE_SCAN_WINDOW 0x0010

int main() {
    int dev_id = hci_get_route(NULL);
    int sock = hci_open_dev(dev_id);
    if (dev_id < 0 || sock < 0) {
        perror("Failed to access Bluetooth adapter");
        exit(EXIT_FAILURE);
    }

    // Set LE scan parameters
    struct hci_le_set_scan_parameters_cp scan_params = {
        .type = 0x01, // Active scan
        .interval = htobs(LE_SCAN_INTERVAL),
        .window = htobs(LE_SCAN_WINDOW),
        .own_bdaddr_type = 0x00, // Public address
        .filter_policy = 0x00    // Accept all devices
    };

    if (hci_le_set_scan_parameters(sock, &scan_params, 1000) < 0) {
        perror("Failed to set scan parameters");
        close(sock);
        exit(EXIT_FAILURE);
    }

    // Start scanning
    uint8_t enable = 1;
    uint8_t filter_dup = 0;
    if (hci_le_set_scan_enable(sock, enable, filter_dup, 1000) < 0) {
        perror("Failed to start scan");
        close(sock);
        exit(EXIT_FAILURE);
    }

    printf("Scanning for BLE devices (Ctrl+C to stop)...\n");
    unsigned char buf[HCI_MAX_EVENT_SIZE];
    struct hci_event_hdr *hdr;
    struct le_advertising_info *info;

    while (1) {
        int len = read(sock, buf, sizeof(buf));
        if (len < 0) {
            perror("Read error");
            break;
        }

        hdr = (struct hci_event_hdr *)buf;
        if (hdr->evt == EVT_LE_META_EVENT) {
            struct le_meta_event *meta = (struct le_meta_event *)(buf + 1);
            if (meta->subevent == EVT_LE_ADVERTISING_REPORT) {
                int num_reports = meta->data[0];
                uint8_t *ptr = meta->data + 1;
                for (int i = 0; i < num_reports; i++) {
                    info = (struct le_advertising_info *)ptr;
                    char addr[18];
                    ba2str(&info->bdaddr, addr);
                    printf("Device: %s | RSSI: %d dBm\n", addr, (int8_t)info->data[info->length]);
                    ptr += info->length + 2;
                }
            }
        }
    }

    // Cleanup
    enable = 0;
    hci_le_set_scan_enable(sock, enable, filter_dup, 1000);
    close(sock);
    return 0;
}

Compile with: gcc -o ble_rssi_scan ble_rssi_scan.c -lbluetooth
Run with: sudo ./ble_rssi_scan

内容的提问来源于stack exchange，提问作者 Cheol