arduino yun ： ATmega32U4 and AR9331 how to bridge？

Official Hardware Classic Yún
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ATmega32U4 and AR9331 Communication by bridge， so bridge is how to work? Whats the bridge Protocol ? Whats the bridge algorithm?
Who can help me? Tahnks

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mowster:
https://www.arduino.cc/en/Guide/ArduinoYun#toc19

thank you~