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执行usb_msd_poll(),插入usb线,p1_0自动拉高。



    我在UBL程序中,在进入usb poll之前,将P1_0设置为输出低。在没有插入usb线时,P1_0为低,但是当插入usb线,进入升级模式后,P1_0被自动拉高了。如果在while(1)循环中comment掉usb_msd_poll(),P1_0就不会被自动拉高。请问usb_msd_poll()接口中对io做了什么操作吗?