Bluedroid use a set of timer function pairs such as btu_start_timer/btu_stop_timer, btu_sys_start_timer/btu_sys_stop_timer for use, in a lack of timer release functions. Thus the timers may be exhausted after some event sequence such as repetition of connection/reconnection with different devices. The maximum timer number used in bluedroid is given by ALARM_CBS_NUM which is 30 for now. This bugfix borrowed some update from bluedroid in Andoroid 7.0, which add timer release functions which promote the recycle of timer resources.
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