在电脑或手机上，搜寻和连接蓝牙设备时，不同的蓝牙设备显示的图标是不同的，比如搜到或连接上的设备是一个蓝牙键盘，显示的就会是键盘图标，如果搜索到的设备是一个手柄，显示的就是一个手柄图标。
显示的图标是根据搜到或连接上的设备类型信息而显示的，这个信息就是COD（class of device）信息。这个信息是在Discovery过程中搜索周围的蓝牙设备时，搜索方从被搜到的设备那里得到的。然后依据COD来判断设备类型，决定显示什么样的图标。
在进行蓝牙产品开发时，通过设置这个信息，就可以显示跟你的产品相匹配的图标。注意这个COD信息主要使用在BR/EDR经典蓝牙上。对于BLE，一般使用的的是广播数据中有两个字节的appearance，而不是三个字节的COD信息。
具体的Class of Device信息介绍如下。
COD信息由四部分组成：
- A Major Service Classes bitfield // 主要服务类型
- A Major Device Class enumerated value // 主要设备类型
- The Minor Device Classes // 次要设备类型
- A fixed value of 0b00 in the two least significant bits // 固定的最低两位bit的值为0
主要设备类型不同，次要设备类型值的含义也不同。
COD信息的结构定义如下：
Major Service Classes
Last Modified: 2022-05-25
| Bit |
Class of Device Major Service Class |
| 13 |
Limited Discoverable Mode |
| 14 |
LE audio |
| 15 |
Reserved for future use |
| 16 |
Positioning (Location identification) |
| 17 |
Networking (LAN, Ad hoc, ...) |
| 18 |
Rendering (Printing, Speakers, ...) |
| 19 |
Capturing (Scanner, Microphone, ...) |
| 20 |
Object Transfer (vInbox, vFolder, ...) |
| 21 |
Audio (Speaker, Microphone, Headset service, ...) |
| 22 |
Telephony (Cordless telephony, Modem, Headset service, ...) |
| 23 |
Information (WEBserver, WAPserver, ...) |
这个是每个位表示一种类型。
Major Device Classes
| 12 |
11 |
10 |
9 |
8 |
Major Device Class |
| 0 |
0 |
0 |
0 |
0 |
Miscellaneous |
| 0 |
0 |
0 |
0 |
1 |
Computer (desktop, notebook, PDA, organizer, ...) |
| 0 |
0 |
0 |
1 |
0 |
Phone (cellular, cordless, pay phone, modem, ...) |
| 0 |
0 |
0 |
1 |
1 |
LAN/Network Access point |
| 0 |
0 |
1 |
0 |
0 |
Audio/Video (headset, speaker, stereo, video display, VCR, ...) |
| 0 |
0 |
1 |
0 |
1 |
Peripheral (mouse, joystick, keyboard, ...) |
| 0 |
0 |
1 |
1 |
0 |
Imaging (printer, scanner, camera, display, ...) |
| 0 |
0 |
1 |
1 |
1 |
Wearable |
| 0 |
1 |
0 |
0 |
0 |
Toy |
| 0 |
1 |
0 |
0 |
1 |
Health |
| 1 |
1 |
1 |
1 |
1 |
Uncategorized: device code not specified |
Minor Device Class field – Computer Major Class
如果主要设备类型是电脑，次要设备类型信息如下：
| 7 |
6 |
5 |
4 |
3 |
2 |
Minor Device Class |
| 0 |
0 |
0 |
0 |
0 |
0 |
Uncategorized, code for device not assigned |
| 0 |
0 |
0 |
0 |
0 |
1 |
Desktop workstation |
| 0 |
0 |
0 |
0 |
1 |
0 |
Serverclass computer |
| 0 |
0 |
0 |
0 |
1 |
1 |
Laptop |
| 0 |
0 |
0 |
1 |
0 |
0 |
Handheld PC/PDA (clamshell) |
| 0 |
0 |
0 |
1 |
0 |
1 |
Palmsize PC/PDA |
| 0 |
0 |
0 |
1 |
1 |
0 |
Wearable computer (watch size) |
| 0 |
0 |
0 |
1 |
1 |
1 |
Tablet |
Minor Device Class field – Phone Major Class
如果主要设备类型是手机，次要设备类型信息如下:
| 7 |
6 |
5 |
4 |
3 |
2 |
Minor Device Class |
| 0 |
0 |
0 |
0 |
0 |
0 |
Uncategorized, code for device not assigned |
| 0 |
0 |
0 |
0 |
0 |
1 |
Cellular |
| 0 |
0 |
0 |
0 |
1 |
0 |
Cordless |
| 0 |
0 |
0 |
0 |
1 |
1 |
Smartphone |
| 0 |
0 |
0 |
1 |
0 |
0 |
Wired modem or voice gateway |
| 0 |
0 |
0 |
1 |
0 |
1 |
Common ISDN access |
Minor Device Class field – LAN/Network Access point Major Class
| 7 |
6 |
5 |
Minor Device Class |
| 0 |
0 |
0 |
Fully available |
| 0 |
0 |
1 |
1% to 17% utilized |
| 0 |
1 |
0 |
17% to 33% utilized |
| 0 |
1 |
1 |
33% to 50% utilized |
| 1 |
0 |
0 |
50% to 67% utilized |
| 1 |
0 |
1 |
67% to 83% utilized |
| 1 |
1 |
0 |
83% to 99% utilized |
| 1 |
1 |
1 |
No service available |
| 4 |
3 |
2 |
Minor Device Class |
| 0 |
0 |
0 |
Uncategorized (use this value if no others apply) |
Minor Device Class field – Audio/Video Major Class
| 7 |
6 |
5 |
4 |
3 |
2 |
Minor Device Class |
| 0 |
0 |
0 |
0 |
0 |
0 |
Uncategorized, code not assigned |
| 0 |
0 |
0 |
0 |
0 |
1 |
Wearable Headset Device |
| 0 |
0 |
0 |
0 |
1 |
0 |
Handsfree Device |
| 0 |
0 |
0 |
0 |
1 |
1 |
(Reserved) |
| 0 |
0 |
0 |
1 |
0 |
0 |
Microphone |
| 0 |
0 |
0 |
1 |
0 |
1 |
Loudspeaker |
| 0 |
0 |
0 |
1 |
1 |
0 |
Headphones |
| 0 |
0 |
0 |
1 |
1 |
1 |
Portable Audio |
| 0 |
0 |
1 |
0 |
0 |
0 |
Car Audio |
| 0 |
0 |
1 |
0 |
0 |
1 |
Settop box |
| 0 |
0 |
1 |
0 |
1 |
0 |
HiFi Audio Device |
| 0 |
0 |
1 |
0 |
1 |
1 |
VCR |
| 0 |
0 |
1 |
1 |
0 |
0 |
Video Camera |
| 0 |
0 |
1 |
1 |
0 |
1 |
Camcorder |
| 0 |
0 |
1 |
1 |
1 |
0 |
Video Monitor |
| 0 |
0 |
1 |
1 |
1 |
1 |
Video Display and Loudspeaker |
| 0 |
1 |
0 |
0 |
0 |
0 |
Video Conferencing |
| 0 |
1 |
0 |
0 |
0 |
1 |
(Reserved) |
| 0 |
1 |
0 |
0 |
1 |
0 |
Gaming/Toy |
Minor Device Class field – Peripheral Major Class
| 7 |
6 |
Minor Device Class |
| 0 |
0 |
Uncategorized, code not assigned |
| 0 |
1 |
Keyboard |
| 1 |
0 |
Pointing device |
| 1 |
1 |
Combo Keyboard/Pointing device |
| 5 |
4 |
3 |
2 |
Minor Device Class |
| 0 |
0 |
0 |
0 |
Uncategorized, code not assigned |
| 0 |
0 |
0 |
1 |
Joystick |
| 0 |
0 |
1 |
0 |
Gamepad |
| 0 |
0 |
1 |
1 |
Remote control |
| 0 |
1 |
0 |
0 |
Sensing device |
| 0 |
1 |
0 |
1 |
Digitizer tablet |
| 0 |
1 |
1 |
0 |
Card Reader (e.g. SIM Card Reader) |
| 0 |
1 |
1 |
1 |
Digital Pen |
| 1 |
0 |
0 |
0 |
Handheld scanner for barcodes, RFID, etc. |
| 1 |
0 |
0 |
1 |
Handheld gestural input device (e.g., “wand” form factor) |
Minor Device Class field – Imaging Major Class
| 7 |
6 |
5 |
4 |
Minor Device Class |
| X |
X |
X |
1 |
Display |
| X |
X |
1 |
X |
Camera |
| X |
1 |
X |
X |
Scanner |
| 1 |
X |
X |
X |
Printer |
| 3 |
2 |
Minor Device Class |
| 0 |
0 |
Uncategorized, default |
Minor Device Class field – Wearable Major Class
| 7 |
6 |
5 |
4 |
3 |
2 |
Minor Device Class |
| 0 |
0 |
0 |
0 |
0 |
1 |
Wristwatch |
| 0 |
0 |
0 |
0 |
1 |
0 |
Pager |
| 0 |
0 |
0 |
0 |
1 |
1 |
Jacket |
| 0 |
0 |
0 |
1 |
0 |
0 |
Helmet |
| 0 |
0 |
0 |
1 |
0 |
1 |
Glasses |
Minor Device Class field – Toy Major Class
| 7 |
6 |
5 |
4 |
3 |
2 |
Minor Device Class |
| 0 |
0 |
0 |
0 |
0 |
1 |
Robot |
| 0 |
0 |
0 |
0 |
1 |
0 |
Vehicle |
| 0 |
0 |
0 |
0 |
1 |
1 |
Doll/Action figure |
| 0 |
0 |
0 |
1 |
0 |
0 |
Controller |
| 0 |
0 |
0 |
1 |
0 |
1 |
Game |
Minor Device Class field – Health Major Class
| 7 |
6 |
5 |
4 |
3 |
2 |
Minor Device Class |
| 0 |
0 |
0 |
0 |
0 |
0 |
Undefined |
| 0 |
0 |
0 |
0 |
0 |
1 |
Blood Pressure Monitor |
| 0 |
0 |
0 |
0 |
1 |
0 |
Thermometer |
| 0 |
0 |
0 |
0 |
1 |
1 |
Weighing Scale |
| 0 |
0 |
0 |
1 |
0 |
0 |
Glucose Meter |
| 0 |
0 |
0 |
1 |
0 |
1 |
Pulse Oximeter |
| 0 |
0 |
0 |
1 |
1 |
0 |
Heart/Pulse Rate Monitor |
| 0 |
0 |
0 |
1 |
1 |
1 |
Health Data Display |
| 0 |
0 |
1 |
0 |
0 |
0 |
Step Counter |
| 0 |
0 |
1 |
0 |
0 |
1 |
Body Composition Analyzer |
| 0 |
0 |
1 |
0 |
1 |
0 |
Peak Flow Monitor |
| 0 |
0 |
1 |
0 |
1 |
1 |
Medication Monitor |
| 0 |
0 |
1 |
1 |
0 |
0 |
Knee Prosthesis |
| 0 |
0 |
1 |
1 |
0 |
1 |
Ankle Prosthesis |
| 0 |
0 |
1 |
1 |
1 |
0 |
Generic Health Manager |
| 0 |
0 |
1 |
1 |
1 |
1 |
Personal Mobility Device |
举个例子，比如我手里拿的是一把带camera的扫描枪，使用蓝牙的SPP串口协议连接电脑，可以传输数据包括图像，它的COD就是：
MAJOR_SERVICE_CLASS = 0x40 // Capturing (Scanner, Microphone, ...)
MAJOR_DEVICE_CLASS = 0x06 // Imaging (printer, scanner, camera, display, ...)
MINOR_DEVICE_CLASS = 0x18 // Camera + Scanner
Byte2：0x08
Byte1：0x06
Byte0：0x60
如果我拿的是一个蓝牙键盘：
MAJOR_SERVICE_CLASS = 0x00 // 无
MAJOR_DEVICE_CLASS = 0x05 // Peripheral (mouse, joystick, keyboard, ...)
MINOR_DEVICE_CLASS = 0x10 // Keyboard
Byte2：0x00
Byte1：0x05
Byte0：0x40
关于COD信息的操作的宏：
typedef struct _tagClass_of_Device_t
{
Byte_t Class_of_Device0;
Byte_t Class_of_Device1;
Byte_t Class_of_Device2;
} Class_of_Device_t;
#define GET_CLASS_OF_DEVICE_FORMAT_TYPE(_x) \
((Byte_t)((_x).Class_of_Device0 & 0x03))
#define SET_CLASS_OF_DEVICE_FORMAT_TYPE(_x, _y) \
((_x).Class_of_Device0 = ((_x).Class_of_Device0 & 0xFC) | ((_y) & 0x03))
#define GET_MAJOR_SERVICE_CLASS(_x) \
((Word_t)(((_x).Class_of_Device2 << 0x03) | ((_x).Class_of_Device1 >> 0x05)))
#define SET_MAJOR_SERVICE_CLASS(_x, _y) \
{ \
(_x).Class_of_Device2 = (Byte_t)(((_y) & 0x7FF) >> 0x03); \
(_x).Class_of_Device1 &= (Byte_t)0x1F; \
(_x).Class_of_Device1 |= (Byte_t)((((_y) & 0xFF) << 0x05) & 0xFF); \
}
#define GET_MAJOR_DEVICE_CLASS(_x) \
((Byte_t)((_x).Class_of_Device1 & 0x1F))
#define SET_MAJOR_DEVICE_CLASS(_x, _y) \
{ \
(_x).Class_of_Device1 &= 0xE0; \
(_x).Class_of_Device1 |= (Byte_t)((_y) & 0x1F); \
}
#define GET_MINOR_DEVICE_CLASS(_x) \
((Byte_t)((_x).Class_of_Device0 >> 0x02))
#define SET_MINOR_DEVICE_CLASS(_x, _y) \
{ \
(_x).Class_of_Device0 &= (Byte_t)0x03; \
(_x).Class_of_Device0 |= (Byte_t)(((_y) << 0x02) & 0xFC); \
}
#define ASSIGN_CLASS_OF_DEVICE(_dest, _x, _y, _z) \
{ \
(_dest).Class_of_Device0 = (_z); \
(_dest).Class_of_Device1 = (_y); \
(_dest).Class_of_Device2 = (_x); \
参考：
Requesting Assigned Numbers – Bluetooth SIG Inc
2.8 Class of Device