采用AT91RM9200的cpu，扩展第三个串口USART，通过这个串口，测试ARM与ARM的通信。此时，系统有三个可用串口，ttyS0（RS232），ttyS1（arm与arm），ttyS2（arm与AVR）-Using AT91RM9200 the cpu, expansion of the third serial port USART, through this serial port, testing, ARM and ARM communication. At this point, the system has three available serial port, ttyS0 (RS232), ttyS1 (arm and arm), ttyS2 (arm and AVR)