This paper describes the design and implementation of UART downloading with Ymodem protocol for multi-process micro-kernel embedded operating system on ARM, including overview of commonly used communication protocols via serial port (Xmodem, Ymodem, and Zmodem), key techniques of Ymodem protocol, design of the system call for Ymodem downloading, and programming essentials of shell command rx with Ymodem protocol. A demo example is provided at the final of the paper to show the usage and effect of the shell command. Practice proves that the performance and efficiency of Ymodem protocol is superior to that of Xmodem, while the program structure of it is simpler than that of Zmodem. Therefore, Ymodem protocol is particularly suitable for implementing downloading function with UART for embedded operating system.
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