Ericir3

Thanks for your reply and i'll try it. I think there's a small mistake in README.md that MPU9250 uses I2C3 but not I2C4(注：如需使用，会占用I2C扩展口(I2C4)，因此其它器件的I2C slave地址不要与它(7位地址0x68/0x69)冲突。). Hope you can confirm that.

In file "pin_mux.c", there is no pin settings for LPI2C3 or LPUART4. I just wonder how you realize I2C or UART transmit and receive functions with micropython?