Linux下基于libmad的mp3播放程序，修改了自带的minimad，重定义了putchar，向真正的音频设备输出。-Linux under the libmad based mp3 player, modify the built-in minimad, re-define putchar, to the real output of audio equipment.

alchemy uart putchar for Linux v2.13.6.

Linux Device Driver: prom exit to mon(), prom enter mon(), prom putchar() .