Linux Bluetooth Programming in C

How to connect BLE devices using Linux bluetooth C library

This is what the old hci_xxx bluetooth C functions are doing at the lowest level. They probably don't work now because bluez/dbus is getting in the way. The following code works on a Raspberry Pi because it disables bluez first, and could be the basis of a C program - but it would be much easier to use one of the github libraries mentioned in the comments.

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
#include <sys/socket.h>
#include <sys/ioctl.h>

struct sockaddr_hci
  {
  unsigned short hci_family;
  unsigned short hci_dev;      
  unsigned short hci_channel;
  };

  
struct hci_filter
  {
  unsigned long type_mask;
  unsigned long event_mask[2];
  unsigned short opcode;
  };

#define BTPROTO_HCI 1
#define SOL_HCI 0
#define HCI_FILTER 2
#define HCIDEVDOWN 0x400448CA

unsigned char eventmask[16] =  { 1,1,0x0C,8,0xFF,0xFF,0xFB,0xFF,0x07,0xF8,0xBF,0x3D }; 
unsigned char lemask[16] = { 0x01,0x01,0x20,0x08,0xBF,0x05,0,0,0,0,0,0 };
unsigned char leopen[30] = {1,0x0D,0x20,0x19,0x60,0,0x60,0,0,0,0x66,0x55,0x44,0x33,0x22,0x11,0,0x18,0,0x28,0,0,0,0x11,0x01,0,0,0,0}; 

int main()
  {
  int n,len,dd;
  struct sockaddr_hci sa;
  struct hci_filter flt;
  char buf[256];
  
  // set board address 00:1E:C0:2D:17:7C
  leopen[15] = 0x00;
  leopen[14] = 0x1E;
  leopen[13] = 0xC0;
  leopen[12] = 0x2D;
  leopen[11] = 0x17;
  leopen[10] = 0x7C;
  
  dd = socket(31, SOCK_RAW | SOCK_CLOEXEC | SOCK_NONBLOCK, BTPROTO_HCI);

  if(dd < 0)
    {
    printf("Socket open error\n");
    return(0);
    }
        
  ioctl(dd,HCIDEVDOWN,0);  // hci0
  close(dd); 
 
     
   // AF_BLUETOOTH=31
  dd = socket(31, SOCK_RAW | SOCK_CLOEXEC | SOCK_NONBLOCK, BTPROTO_HCI);

  if(dd < 0)
    {
    printf("Socket open error\n");
    return(0);
    }

  sa.hci_family = 31;   // AF_BLUETOOTH;
  sa.hci_dev = 0;       // hci0/1/2...
  sa.hci_channel = 1;   // HCI_CHANNEL_USER    
  
  if(bind(dd,(struct sockaddr *)&sa,sizeof(sa)) < 0)
    {
    printf("Bind failed\n");
    close(dd);
    return(0);
    }

  write(dd,eventmask,12);
  write(dd,lemask,12);  

  printf("Send hci LE connect\n"); 
  write(dd,leopen,29);
  
  printf("If get reply = 04 3E 13 01 00.. then has connected OK\n");  
  printf("REPLY =");
  for(n = 0 ; n < 10 ; ++ n)
    {
    len = read(dd,buf,sizeof(buf));
    for(n = 0 ; n < len ; ++n)
      printf(" %02X",buf[n]);
    printf("\n");
    sleep(1);
    }
  printf("\nExit and disconnect\n");
  }

Linux Bluetooth programming in C & socket.h

For the second question: you have to post the code you've written. Else we can't figure out what's bad.

For the first question: you need to put the library linker flags as the last parameters when invoking GCC:

gcc nxt_bt_connect.c -o nxt_bt_connect -lm -lbluetooth

Bluetooth interface control in C code ( Linux OS )

You can use the c code for hciconfig itself. Just download the BlueZ source and open tools/hciconfig.c and use the following functions:-

static void cmd_up(int ctl, int hdev, char *opt)
{
    ...
}

and

static void cmd_down(int ctl, int hdev, char *opt) 
{
    ... 
}

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