The ble-nrf51822 implementation of the BLE API generated callbacks for radio
notification events without using the minar scheduler and at very high
priority. This functionality is replaced by posting events through minar
when YOTTA_CFG_MBED_OS is defined. Note that minar could not be used directly
to post callbacks because radio notification events are handled at very high
priority, which caused a hard-fault when minar tries to enter a critical
section. Alternatively, a Timeout was used to post the callback in another
context with lower priority.
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