duo/main.cpp: fix the issue that the system loop is block.
duo/main.cpp: fix the issue that the system loop is block.

ganshun666/micropython,redbear/micropython,redbear/micropython,redbear/micropython,redbear/micropython,redbear/micropython,ganshun666/micropython,ganshun666/micropython,ganshun666/micropython,ganshun666/micropython