蓝牙ctl中读写特性acquire-write操作失败问题排查

问题描述 #

通过bluetoothctl连接智能手表后，确认UUID为6e400002-b5a3-f393-e0a9-e50e24dcca9e的特征具备读写能力，但选中该属性执行acquire-write时，提示：

Failed to acquire write: org.bluez.Error.NotSupported

命令行操作日志 #

linaro@linaro-alip:~$ bluetoothctl
Agent registered
[bluetooth]# pair 00:18:80:81:FE:81
Attempting to pair with 00:18:80:81:FE:81
[CHG] Device 00:18:80:81:FE:81 Connected: yes
[CHG] Device 00:18:80:81:FE:81 Paired: yes
Pairing successful
[CHG] Device 00:18:80:81:FE:81 ServicesResolved: yes
[Cordio]# menu gatt
[Cordio]# list-attributes
Primary Service
    /org/bluez/hci0/dev_00_18_80_81_FE_81/service0020
    6e400000-b5a3-f393-e0a9-e50e24dcca9e
    Vendor specific
Characteristic
    /org/bluez/hci0/dev_00_18_80_81_FE_81/service0020/char0024
    6e400002-b5a3-f393-e0a9-e50e24dcca9e
    Nordic UART TX
Characteristic
    /org/bluez/hci0/dev_00_18_80_81_FE_81/service0020/char0021
    6e400001-b5a3-f393-e0a9-e50e24dcca9e
    Nordic UART Service
Descriptor
    /org/bluez/hci0/dev_00_18_80_81_FE_81/service0020/char0021/desc0023
    00002902-0000-1000-8000-00805f9b34fb
    Client Characteristic Configuration
Primary Service
    /org/bluez/hci0/dev_00_18_80_81_FE_81/service0010
    00001801-0000-1000-8000-00805f9b34fb
    Generic Attribute Profile
Characteristic
    /org/bluez/hci0/dev_00_18_80_81_FE_81/service0010/char0011
    00002a05-0000-1000-8000-00805f9b34fb
    Service Changed
Descriptor
    /org/bluez/hci0/dev_00_18_80_81_FE_81/service0010/char0011/desc0013
    00002902-0000-1000-8000-00805f9b34fb
    Client Characteristic Configuration
[Cordio]# attribute-info 6e400002-b5a3-f393-e0a9-e50e24dcca9e
Characteristic - Nordic UART TX
    UUID: 6e400002-b5a3-f393-e0a9-e50e24dcca9e
    Service: /org/bluez/hci0/dev_00_18_80_81_FE_81/service0020
    Value:
  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  00 00 00 00                                      ....            
    Flags: read
    Flags: write
[Cordio]# select-attribute 6e400002-b5a3-f393-e0a9-e50e24dcca9e
[Cordio:/service0020/char0024]# write 0x55
Attempting to write /org/bluez/hci0/dev_00_18_80_81_FE_81/service0020/char0024
[Cordio:/service0020/char0024]# acquire-write
Failed to acquire write: org.bluez.Error.NotSupported
[Cordio:/service0020/char0024]# read
Attempting to read /org/bluez/hci0/dev_00_18_80_81_FE_81/service0020/char0024
[CHG] Attribute /org/bluez/hci0/dev_00_18_80_81_FE_81/service0020/char0024 Value:
  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  00 00 00 00                                      ....            
  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  00 00 00 00                                      ....            

原因解析 #

1. acquire-write的适用条件不满足 #

acquire-write是BlueZ中用于获取流式写入句柄的命令，仅支持两种场景：

• 特征带有write-with-response flag（带响应写入）
• 特征支持**可靠写入（Reliable Write）**机制

但从attribute-info的输出可以看到，目标特征仅标注了write flag，这个flag对应无响应写入（Write Without Response），不满足acquire-write的使用要求，因此返回不支持的错误。

2. Nordic UART服务的设计特性 #

你操作的是Nordic UART服务的TX特征，该服务的设计逻辑是：

• TX特征（6e400002-...）用于主机向设备发送数据，默认使用无响应写入来提升传输效率，不需要设备返回确认
• 从日志也能验证：直接执行write 0x55是成功的，说明普通无响应写入功能正常，只是acquire-write对应的机制不被该特征支持

3. 特征flag的明确区分 #

BLE特征的写入相关flag有明确差异：

• write：无响应写入，发送后无需设备确认，适合低延迟批量传输
• write-with-response：带响应写入，每次写入需设备确认，支持acquire-write的流式操作

你的目标特征只有write flag，没有write-with-response，所以不支持acquire-write命令。

内容的提问来源于stack exchange，提问作者Utku Gökçe