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一、概念
1、依赖关系：
2、配置和角色
注：HFP并没有master与slave的区分，在建立HFP通信前，LMP link是必须的；
3、支持的功能
其中编解码方式可以看到CVSD是必须支持的，mSBC不是必须支持的，
4、AT command
HFP使用AT command的子集来发送命令；
（1）格式HFP中通过AT command来发送命令，响应，我们来看下命令格式说明：
（2）HFP AT command命令子集如下图：
|
序号 |
命令参数 |
说明 |
|
1 |
ATA |
Standard call answer AT command. |
|
2 |
ATDdd…dd |
Standard AT command intended for placing a call to a phone number |
|
3 |
ATD>nnn |
Extension of the standard ATD command, intended for memory dialing |
|
4 |
ERROR |
Standard error indication code |
|
5 |
OK |
Standard acknowledgement to the execution of a command |
|
6 |
NO CARRIER, BUSY, NO ANSWER, DELAYED, BLACKLISTED |
Extended response indication codes for AT commands. |
|
7 |
RING |
Standard ―incoming call‖ indication |
|
8 |
AT+CCWA |
Standard ―Call Waiting notification‖ AT command. |
|
+CCWA |
Standard ―Call Waiting notification‖ unsolicited result code. |
|
|
AT+CHLD |
Standard call hold and multiparty handling AT command. |
|
|
AT+CHUP |
Standard hang-up AT command. Execution command causes the AG to terminate the currently active call. |
|
|
AT+CIND |
Standard indicator update AT command. |
|
|
+CIND |
Standard list of current phone indicators |
|
|
AT+CLCC |
Standard list current calls command. |
|
|
+CLCC |
Standard list current calls result code. |
|
|
AT+COPS |
The AT+COPS=3,0 shall be sent by the HF to the AG prior to sending the AT+COPS? command. AT+COPS=3,0 sets the format of the network operator string to the long format alphanumeric. The AT+COPS? command is used for reading network operator. This profile shall only support the “reading” of the name of the network operator. The response to this command from the AG shall return a +COPS:<mode>,<format>,<operator> where: <mode> contains the current mode and provides no information with regard to the name of the operator. BLUETOOTH SPECIFICATION Page 80 of 126 Hands-Free Profile 1.6 10 May 2011 <format> specifies the format of the <operator> parameter string, and shall always be 0 for this specification. <operator> specifies a quoted string in alphanumeric format representing the name of the network operator. This string shall not exceed 16 characters. |
|
|
AT+CMEE |
Standard AT command used to enable the use of result code +CME ERROR: <err> as an indication of an error relating to the functionality of the AG. The set command AT+CMEE=1 is covered in this specification. |
|
|
+CME ERROR |
+CME ERROR: 0 – AG failure +CME ERROR: 1 – no connection to phone +CME ERROR: 3 – operation not allowed +CME ERROR: 4 – operation not supported +CME ERROR: 5 – PH-SIM PIN required +CME ERROR: 10 – SIM not inserted +CME ERROR: 11 – SIM PIN required +CME ERROR: 12 – SIM PUK required +CME ERROR: 13 – SIM failure +CME ERROR: 14 – SIM busy +CME ERROR: 16 – incorrect password +CME ERROR: 17 – SIM PIN2 required +CME ERROR: 18 – SIM PUK2 required +CME ERROR: 20 – memory full +CME ERROR: 21 – invalid index +CME ERROR: 23 – memory failure +CME ERROR: 24 – text string too long +CME ERROR: 25 – invalid characters in text string +CME ERROR: 26 – dial string too long +CME ERROR: 27 – invalid characters in dial string +CME ERROR: 30 – no network service +CME ERROR: 31 – network Timeout. +CME ERROR: 32 – network not allowed – Emergency calls only |
|
|
AT+CLIP |
Standard ―Calling Line Identification notification‖ activation AT command. |
|
|
+CLIP |
Standard ―Calling Line Identification notification‖ unsolicited result code. |
|
|
AT+CMER |
Standard event reporting activation/deactivation AT command. |
|
|
+CIEV |
Standard ―indicator events reporting‖ unsolicited result code. |
|
|
AT+VTS |
Standard DTMF generation AT command. |
|
|
AT+CNUM |
Syntax: AT+CNUM (Retrieve Subscriber Number Information) AT+CNUM=? (Test Subscriber Number Information – Not Implemented) Description: Command issued by HF for the ―Subscriber Number Information‖ feature in the AG. Only the action command AT+CNUM format is used. |
|
|
+CNUM |
Syntax: +CNUM: [<alpha>],<number>, <type>,[<speed> ,<service>] (Response for AT+CNUM) Description: Standard Response used for sending the ―Subscriber Number Information‖ from AG to HF. The AG shall send the +CNUM: response for the AT+CNUM from the HF. Values: – <alpha>: This optional field is not supported, and shall be left blank. – <number>: Quoted string containing the phone number in the format specified by <type>. – <type> field specifies the format of the phone number provided, and can be one of the following values: o values 128-143: The phone number format may be a national or international format, and may contain prefix and/or escape digits. No changes on the number presentation are required. o values 144-159: The phone number format is an international number, including the country code prefix. If the plus sign (“+”) is not included as part of the number and shall be added by the AG as needed. – values 160-175: National number. No prefix nor escape digits included. – <speed>: This optional field is not supported, and shall be left blank. – <service>: Indicates which service this phone number relates to. Shall be either 4 (voice) or 5 (fax). Example: +CNUM: ,””,129,,4 |
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二、HFP通信流程
上图中的Table3.1给出了HFP支持的feature，这里我们只看1-7，后面的可以自己去翻下spec；
1、HFP Service Level Connection Establishment
使用HFP时，第一步就是初始化Service Level Connection Establishment，可以由AG或HF发起；Service Level Connection是基于RFCOMM data link chaanel，流程图如下：
b、第二步是基于第一步，如果AG和HF都支持Codec Negotiation feature，则发送AT+BAC命令，由HF告知AG支持的codecs；
c、第三步AT+CIND是得到支持的indicators和其顺序；
d、第四步：HF使用AT+CMER使能AG端的“Indicators status update”功能这样AG端就可以主动上报状态的改变，无论是服务，电话等；
e、第五步：如果支持“Call waiting and 3-way calling”feature，则使用AT+CHLD获取信息；
这样，就建立了HFP通信，当发生断链时，HF会在超时后主动再次发起HFP Service Level Connection Establishment连接；
我们看下AT+BRSF和BRSF的说明
（1）AT+BRSF (Bluetooth Retrieve Supported Features)
（2）BRSF与AT+BRSF类似；
2、HFP Service Level Connection release
HF和AG都可以发起release，步骤主要是RFCOMM信道的移除；
3、注册状态的传输
当AT+CMER和AT+BIA同时被打开时，AG会主动向HF发送AG’s registration status changes，如下图：
4、信号强度事件通知
当AT+CMER和AT+BIA同时被打开时，AG会主动向HF发送AG’s signal strength changes，如下图：
5、其他，同上面两个通知还有AG’s roaming status changes和 AG’s battery level changes，如下面两个图片：
三、总结
HFP是应用层协议，使用AT command的子集命令来实现自身命令；
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