最近在给一个客户调主从一体的模块，基于S130，距离稍微远一点就会出现连接上后立马又断开连接的现象，
追踪了一下原因，给出的 HCI Error code 是 0x003E，暂且不知道这是什么鬼，查了网上的一个帖子，解释如下：
断开原因0x3e HCI_ERROR_CODE_CONN_FAILED_TO_ESTABLISH
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我用TI CC2640做主机，手机做从机进行数据传输，有时候发现TI作为主机连接上手机后，立刻就会有断开事件，经过跟踪，发现断开原因是
0x3e HCI_ERROR_CODE_CONN_FAILED_TO_ESTABLISH，但是在此之前已有连接建立事件GAP_LINK_ESTABLISHED_EVENT产生，
请IT员工看下为啥会产生这种情况，需要如何应对预防此类问题。
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TI E2E上有相关的帖子 https://e2e.ti.com/support/wireless_connectivity/f/538/t/377682
A "Failed to Establish" (0x3E) error occurs if the master is unable to receive a packet from the slave within the first 6 connection events after sending a connection request. This could be caused a number of reasons. Here are a few possibilities:
- The RF performance on one or both devices is not good, so the slave either never receives the connection request, or the master never receives any packets from the slave during the first 6 connection events. The RF Performance could be bad due to a failed CRC, collision or maybe the devices are just out of range.
- There could be a timing issue in either device. If the link layer clock on either device is not running at 32.768kHz (within the tolerance set using the HCI_Ext_SetSCACmd function; default is +/-50ppm) then the timing will be off and the slave might not be listening at the correct time to receive the master's packets.
- If the slave device is advertising with the whitelist filter policy set to GAP_FILTER_POLICY_WHITE_CONor GAP_FILTER_POLICY_WHITE then the slave will ignore the connection from the master and continue advertising normally, and the master will get the 0x3E error since it does not receive any packets from the slave during the first 6 connection events.