1. 蓝牙简介

蓝牙是一种支持设备短距离通信的无线电技术,使用 2.4GHz 频段,数据速率为1Mbps 。采用时分复用方案实现全双工传输。

蓝牙技术将设备分为两种:主设备和从设备。

蓝牙主设备的特点:主设备一般具有输入端。在进行蓝牙匹配操作时,用户通过输入端可输入随机的匹配密码来将两个设备匹配。蓝牙手机、安装有蓝牙模块的 PC 等都是主设备。(例如:蓝牙手机和蓝牙 PC 进行匹配时,用户可在蓝牙手机上任意输入一组数字,然后在蓝牙PC上输入相同的一组数字,来完成这两个设备之间的匹配。)

蓝牙从设备特点:从设备一般不具备输入端。因此从设备在出厂时,在其蓝牙芯片中,固化有一个4位或6位数字的匹配密码。蓝牙耳机等都是从设备。(例如:蓝牙 PC 与蓝牙耳机匹配时,用户将蓝牙耳机上的匹配密码输入到蓝牙 PC 上,完成匹配。)

蓝牙设备的呼叫过程:

  1. 蓝牙主端设备发起呼叫,首先是查找,找出周围处于可被查找的蓝牙设备,此时从端设备需要处于可被查找状态。
  2. 主端设备找到从端蓝牙设备后,与从端蓝牙设备进行配对,此时需要输入从端设备的 PIN 码。
  3. 配对完成后,从端蓝牙设备会记录主端设备的信任信息,此时主端即可向从端设备发起呼叫,根据应用不同,可能是ACL数据链路呼叫或SCO语音链路呼叫,已配对的设备在下次呼叫时,不再需要重新配对。
  4. 已配对的设备,做为从端的蓝牙耳机也可以发起建链请求,但做数据通讯的蓝牙模块一般不发起呼叫。
  5. 链路建立成功后,主从两端之间即可进行双向的数据通讯。在通信状态下,主端和从端设备都可以发起断链,断开蓝牙链路。

蓝牙协议栈:

  • RFCOMM 叫做电缆替代协议,它在蓝牙基带协议上仿真 RS-232 控制和数据信号,为使用串行线传送机制的上层协议(如 OBEX )提供服务。
  • OBEX 叫做对象交换协议,采用简单的和自发的方式交换目标,用于传输文件。

2. Linux 对蓝牙的支持

2.6 之后的内核都提供了蓝牙支持,通常都已经是默认的设置:

[*] Networking support --->                [CONFIG_NET]
  </M> Bluetooth subsystem support --->    [CONFIG_BT]
    <*/M> RFCOMM protocol support          [CONFIG_BT_RFCOMM]
    [*]   RFCOMM TTY support               [CONFIG_BT_RFCOMM_TTY]
    <*/M> BNEP protocol support            [CONFIG_BT_BNEP]
    [*]   Multicast filter support         [CONFIG_BT_BNEP_MC_FILTER]
    [*]   Protocol filter support          [CONFIG_BT_BNEP_PROTO_FILTER]
    <*/M> HIDP protocol support            [CONFIG_BT_HIDP]
        Bluetooth device drivers --->
          (Select the appropriate drivers for your Bluetooth hardware)

  <*/M> RF switch subsystem support --->   [CONFIG_RFKILL]

Linux 官方的蓝牙协议栈是 BlueZ ,BlueZ 包括 :

  • HCI Core
  • HCI UART, USB and Virtual HCI device drivers
  • L2CAP module
  • Configuration and testing utilities

BlueZ 包提供了蓝牙编程库和各种工具:

  • bccmd : is used to issue BlueCore commands to Cambridge Silicon Radio devices.
  • bluemoon : is a Bluemoon configuration utility.
  • bluetoothctl : is the interactive Bluetooth control program.
  • bluetoothd : is the Bluetooth daemon.
  • btmon : provides access to the Bluetooth subsystem monitor infrastructure for reading HCI traces.
  • ciptool : is used to set up, maintain, and inspect the CIP configuration of the Bluetooth subsystem in the Linux kernel.
  • hciattach : is used to attach a serial UART to the Bluetooth stack as HCI transport interface.
  • hciconfig : is used to configure Bluetooth devices.
  • hcidump : reads raw HCI data coming from and going to a Bluetooth device and prints to screen commands, events and data in a human-readable form.
  • hcitool : is used to configure Bluetooth connections and send some special command to Bluetooth devices.
  • hex2hcd : is used to convert a file needed by Broadcom devices to hcd (Broadcom bluetooth firmware) format.
  • l2ping : is used to send a L2CAP echo request to the Bluetooth MAC address given in dotted hex notation.
  • l2test : is L2CAP testing program.
  • rctest : is used to test RFCOMM communications on the Bluetooth stack.
  • rfcomm : is used to set up, maintain, and inspect the RFCOMM configuration of the Bluetooth subsystem in the Linux kernel.
  • sdptool : is used to perform SDP queries on Bluetooth devices.
  • libbluetooth.so : contains the BlueZ 4 API functions.

安装了 BlueZ 之后,配置文件都在 /etc/bluetooth 目录下。

3. 在 Linux 中配置蓝牙

使用的模块是 Intel 2330 ,同时支持 WIFI 和 Bluetooth 。调试前应该先下载模块的固件 iwlwifi-2030-6.ucode ,放入系统的 /lib/fireware 目录下,系统加载驱动 iwlwifi 时会自动查找。使用的系统是 yocto linux ,运行在 Intel Quark 平台的主板。

系统启动后可以查看设备:

root@WR-IntelligentDevice:~# lsusb
Bus 001 Device 002: ID 0424:2514 Standard Microsystems Corp. USB 2.0 Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 003: ID 8087:07da Intel Corp. 

应该加载的驱动:

root@WR-IntelligentDevice:~# lsmod | grep bt
bluetooth             200527  6 rfcomm,hidp,btusb
btusb                  11506  0 

如果驱动加载成功,会出现蓝牙的设备节点,使用 hciconfig 命令查看:

root@WR-IntelligentDevice:~# hciconfig -a
hci0:   Type: BR/EDR  Bus: USB
        BD Address: 00:15:00:A1:E3:83  ACL MTU: 310:10  SCO MTU: 64:8
        DOWN 
        RX bytes:495 acl:0 sco:0 events:22 errors:0
        TX bytes:369 acl:0 sco:0 commands:22 errors:0
        Features: 0xff 0xff 0x8f 0xfe 0xdb 0xff 0x5b 0x87
        Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 
        Link policy: RSWITCH HOLD SNIFF PARK 
        Link mode: SLAVE ACCEPT 

可以看到设备的状态是 DOWN ,表示蓝牙还没有启动。手动启动蓝牙,可以看到蓝牙状态变为 UP RUNNING ,而且是从设备:

root@WR-IntelligentDevice:~# hciconfig hci0 up
root@WR-IntelligentDevice:~# hciconfig -a 
hci0:   Type: BR/EDR  Bus: USB
        BD Address: 00:15:00:A1:E3:83  ACL MTU: 310:10  SCO MTU: 64:8
        UP RUNNING 
        RX bytes:990 acl:0 sco:0 events:44 errors:0
        TX bytes:738 acl:0 sco:0 commands:44 errors:0
        Features: 0xff 0xff 0x8f 0xfe 0xdb 0xff 0x5b 0x87
        Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3 
        Link policy: RSWITCH HOLD SNIFF PARK 
        Link mode: SLAVE ACCEPT 
        Name: 'PC Controller App v1.4'
        Class: 0x000000
        Service Classes: Unspecified
        Device Class: Miscellaneous, 
        HCI Version: 4.0 (0x6)  Revision: 0x1ebd
        LMP Version: 4.0 (0x6)  Subversion: 0xfc00
        Manufacturer: Intel Corp. (2)

更好的方法是用 bluetoothd 启动蓝牙, bluetoothd 是一个守护进程,启动时会根据 /etc/bluetooth/ 下的配置文件初始化蓝牙,直接执行 bluetoothd

3.1 连接手机蓝牙

打开手机的蓝牙,测试用的是小米手机。这里要注意一点,手机上的蓝牙在打开后会有一段时间处于可检测状态,也就是其他蓝牙设备可以扫描到它,之后会关闭可检测性,这段时间的长短通常可以设置,有的手机在熄屏时也会关闭蓝牙的可检测性。

然后扫描一下周边的蓝牙设备:

root@WR-IntelligentDevice:~# hcitool scan
Scanning ...
        A2:CF:49:FD:99:AF       MI-ONE Plus

scan 用于扫描经典蓝牙设备,如果是低功耗蓝牙设备(BLE),例如手环之类,要 用 lescan 选项,调试 BLE 设备要用 gatttool 工具。

测试能否连通:

root@WR-IntelligentDevice:~# l2ping -i hci0 -c 4 A2:CF:49:FD:99:AF
Ping: A2:CF:49:FD:99:AF from 00:15:00:A1:E3:83 (data size 44) ...
44 bytes from A2:CF:49:FD:99:AF id 0 time 25.03ms
44 bytes from A2:CF:49:FD:99:AF id 1 time 25.32ms
44 bytes from A2:CF:49:FD:99:AF id 2 time 26.96ms
44 bytes from A2:CF:49:FD:99:AF id 3 time 27.06ms
4 sent, 4 received, 0% loss

利用 SDP 协议,我们还可以查看每个设备都有功能,能提供什么服务,每种基于 RFCOMM 的服务都使用某种协议,占据哪个“频道 (channel)”,这是使用服务时的一个重要参数,先看看自己:

root@WR-IntelligentDevice:~# sdptool browse local
Browsing FF:FF:FF:00:00:00 ...
Service Name: SIM Access Server
Service RecHandle: 0x10000
Service Class ID List:
  "SIM Access" (0x112d)
  "Generic Telephony" (0x1204)
Protocol Descriptor List:
  "L2CAP" (0x0100)
  "RFCOMM" (0x0003)
    Channel: 8
Profile Descriptor List:
  "SIM Access" (0x112d)
    Version: 0x0101

Service Name: Headset Audio Gateway
Service RecHandle: 0x10001
Service Class ID List:
  "Headset Audio Gateway" (0x1112)
  "Generic Audio" (0x1203)
Protocol Descriptor List:
  "L2CAP" (0x0100)
  "RFCOMM" (0x0003)
    Channel: 12
Profile Descriptor List:
  "Headset" (0x1108)
    Version: 0x0102

Service Name: Hands-Free Audio Gateway
Service RecHandle: 0x10002
Service Class ID List:
  "Handsfree Audio Gateway" (0x111f)
  "Generic Audio" (0x1203)
Protocol Descriptor List:
  "L2CAP" (0x0100)
  "RFCOMM" (0x0003)
    Channel: 13
Profile Descriptor List:
  "Handsfree" (0x111e)
    Version: 0x0105

Service Name: Audio Source
Service RecHandle: 0x10003
Service Class ID List:
  "Audio Source" (0x110a)
Protocol Descriptor List:
  "L2CAP" (0x0100)
    PSM: 25
  "AVDTP" (0x0019)
    uint16: 0x102
Profile Descriptor List:
  "Advanced Audio" (0x110d)
    Version: 0x0102

Service Name: AVRCP TG
Service RecHandle: 0x10004
Service Class ID List:
  "AV Remote Target" (0x110c)
Protocol Descriptor List:
  "L2CAP" (0x0100)
    PSM: 23
  "AVCTP" (0x0017)
    uint16: 0x103
Profile Descriptor List:
  "AV Remote" (0x110e)
    Version: 0x0104

Service Name: AVRCP CT
Service RecHandle: 0x10005
Service Class ID List:
  "AV Remote" (0x110e)
Protocol Descriptor List:
  "L2CAP" (0x0100)
    PSM: 23
  "AVCTP" (0x0017)
    uint16: 0x103
Profile Descriptor List:
  "AV Remote" (0x110e)
    Version: 0x0100

Service Name: Dial-Up Networking
Service RecHandle: 0x10006
Service Class ID List:
  "Dialup Networking" (0x1103)
  "Generic Networking" (0x1201)
Protocol Descriptor List:
  "L2CAP" (0x0100)
  "RFCOMM" (0x0003)
    Channel: 1
Profile Descriptor List:
  "Dialup Networking" (0x1103)
    Version: 0x0100

再看看手机的蓝牙服务:

root@WR-IntelligentDevice:~# sdptool browse  A2:CF:49:FD:99:AF 
Browsing A2:CF:49:FD:99:AF ...
Service RecHandle: 0x10000
Service Class ID List:
  "PnP Information" (0x1200)
Profile Descriptor List:
  "PnP Information" (0x1200)
    Version: 0x0102

Service Name: Audio Source
Service RecHandle: 0x10001
Service Class ID List:
  "Audio Source" (0x110a)
Protocol Descriptor List:
  "L2CAP" (0x0100)
    PSM: 25
  "AVDTP" (0x0019)
    uint16: 0x102
Profile Descriptor List:
  "Advanced Audio" (0x110d)
    Version: 0x0102

Service Name: AVRCP TG
Service RecHandle: 0x10002
Service Class ID List:
  "AV Remote Target" (0x110c)
Protocol Descriptor List:
  "L2CAP" (0x0100)
    PSM: 23
  "AVCTP" (0x0017)
    uint16: 0x103
Profile Descriptor List:
  "AV Remote" (0x110e)
    Version: 0x0100

Service Name: Voice Gateway
Service RecHandle: 0x10003
Service Class ID List:
  "Handsfree Audio Gateway" (0x111f)
  "Generic Audio" (0x1203)
Protocol Descriptor List:
  "L2CAP" (0x0100)
  "RFCOMM" (0x0003)
    Channel: 10
Profile Descriptor List:
  "Handsfree" (0x111e)
    Version: 0x0105

Service Name: Voice Gateway
Service RecHandle: 0x10004
Service Class ID List:
  "Headset Audio Gateway" (0x1112)
  "Generic Audio" (0x1203)
Protocol Descriptor List:
  "L2CAP" (0x0100)
  "RFCOMM" (0x0003)
    Channel: 11
Profile Descriptor List:
  "Headset" (0x1108)
    Version: 0x0102

Service Name: OBEX Object Push
Service RecHandle: 0x10005
Service Class ID List:
  "OBEX Object Push" (0x1105)
Protocol Descriptor List:
  "L2CAP" (0x0100)
  "RFCOMM" (0x0003)
    Channel: 12
  "OBEX" (0x0008)
Profile Descriptor List:
  "OBEX Object Push" (0x1105)
    Version: 0x0100

Service Name: OBEX Phonebook Access Server
Service RecHandle: 0x10006
Service Class ID List:
  "Phonebook Access - PSE" (0x112f)
Protocol Descriptor List:
  "L2CAP" (0x0100)
  "RFCOMM" (0x0003)
    Channel: 19
  "OBEX" (0x0008)
Profile Descriptor List:
  "Phonebook Access" (0x1130)
    Version: 0x0100

使用 openobex 包提供的 obex_test 工具,在 yocto 的官网可以下载到 recipes 文件和补丁。或者在下载源码:https://github.com/zuckschwerdt/openobex

3.2 连接蓝牙耳机

先启动本地的蓝牙服务并配置:

root@WR-IntelligentDevice:~# bluetoothd
root@WR-IntelligentDevice:~# hciconfig hci0 noencrypt
root@WR-IntelligentDevice:~# hciconfig hci0 piscan
root@WR-IntelligentDevice:~# hciconfig hci0 name "bluez4"
root@WR-IntelligentDevice:~# hciconfig hci0 pageto 65535

然后启动蓝牙耳机,使之处于可检测状态,然后扫描:

root@WR-IntelligentDevice:~# hcitool scan
Scanning ...
        50:C9:71:AA:E0:AE       JABRA EASYGO

准备一个 test.wav 的音频文件,然后用如下脚本测试蓝牙耳机:

#!/bin/sh
local mac="50:C9:71:AA:E0:AE"
local asoundconf="/etc/asound.conf"

#add service    
sdptool add a2snk
sdptool add a2src
sdptool add avrct
sdptool add avrtg
sdptool add hf
sdptool add hs

echo "" >> $asoundconf
echo "pcm.bluetooth{" >> $asoundconf
echo "    type bluetooth" >> $asoundconf
echo "    device $mac" >> $asoundconf
echo "    profile \"hifi\"" >> $asoundconf
echo "}" >> $asoundconf

echo "Bind to $mac ..."
simple-agent hci0 $mac || {
    echo "simple-agent failed!"
    exit 1
}

echo "Connect $mac ..."
bluez-test-audio connect $mac || {
    echo "audio connect failed!"
    exit 1
}

echo "Connection result ..."
hcitool con

echo "Play audio ..."
aplay -D bluetooth ./test.wav

正常情况会打印如下信息,蓝牙耳机可以听到音频内容:

Audio sink service registered
Audio source service registered
Remote control service registered
Remote target service registered
Handsfree service registered
Headset service registered
Bind to 50:C9:71:AA:E0:AE ...
Release
New device (/org/bluez/3319/hci0/dev_50_C9_71_AA_E0_AE)
Connect 50:C9:71:AA:E0:AE ...
Connection result ...
Connections:
        < ACL 50:C9:71:AA:E0:AE handle 34 state 1 lm MASTER AUTH ENCRYPT 
Play audio ...
Playing WAVE './test.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo
Li Shaocheng. Published under BY-NC-SA
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