android ble 连接缓慢 [英] android ble connect slowly
问题描述
我正在编写一个 Android 应用程序来连接到 BLE 外围设备.安卓 4.4.2，银河 Nexus.
Hi I'm writing an Android app to connect to a BLE peripheral device. Android 4.4.2, Galaxy Nexus.
我在设备上有一个 LED 来指示连接状态.
I have an LED on the device to indicate connection state.
问题是从 connectGatt() 调用到接收 onConnectionStateChange STATE_CONNECTED 点的持续时间是如此不一致.有时它非常快，但大部分时间需要 5 秒或更长时间.关闭/打开蓝牙没有任何影响.
The issue is the duration from connectGatt() call to the point of receiving onConnectionStateChange STATE_CONNECTED are so inconsistent. Some time it is very quick but most of the time it takes 5s or more. Turning Bluetooth off/on does not have any effect.
我在带有 TI BLE 加密狗的 PC 上尝试了 TI BTool，它总是能够非常快速地建立连接.
I tried TI BTool on PC with the TI BLE Dongle and it always establishes connection very fast.
我也试过 iPhone 5S，它也很快.
I also tried with an iPhone 5S and it is fast too.
- 有人也遇到过这个问题吗?
- 我们有机会改进吗?
推荐答案
将 true 传递给 connectGatt() autoconnect 参数请求后台连接，而传递 false 请求直接连接.BluetoothGatt#connect() 总是请求后台连接.
Passing true to connectGatt() autoconnect argument requests a background connection, while passing false requests a direct connection. BluetoothGatt#connect() always requests a background connection.
后台连接(根据来自 4.4.2 AOSP 的 Bluedroid 来源)具有 1280 毫秒的扫描间隔和 11.25 毫秒的窗口.这对应于大约 0.9% 的占空比，这解释了为什么连接在不扫描时可能需要很长时间才能完成.
Background connection (according to Bluedroid sources from 4.4.2 AOSP) has scan interval of 1280ms and a window of 11.25ms. This corresponds to about 0.9% duty cycle which explains why connections, when not scanning, can take a long time to complete.
直接连接的间隔为 60 毫秒，窗口为 30 毫秒，因此连接完成得更快.此外，一次只能有一个直接连接请求未决，并且在 30 秒后超时.onConnectionStateChange() 以 state=2、status=133 调用以指示此超时.
Direct connection has interval of 60ms and window of 30ms so connections complete much faster. Additionally there can only be one direct connection request pending at a time and it times out after 30 seconds. onConnectionStateChange() gets called with state=2, status=133 to indicate this timeout.
我已经在 Nexus5 上验证了这种行为，但显然是 YMMV.
I have verified this behavior on Nexus5 but obviously YMMV.
我应该提一下，BluetoothGatt.java 中有一个竞争条件，即使将 autoconnect=true 传递给 BluetoothDevice#connectGatt()，它也会导致直接连接请求.
I should mention that there is a race condition in BluetoothGatt.java that can cause a direct connection request even if autoconnect=true is passed into BluetoothDevice#connectGatt().
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