学习嵌入式要打好基础，弄懂基本的硬件接口gpio，在和硬件平台打交道中就不怕了-The learning embedded to lay a solid foundation to understand the basic hardware interface gpio not afraid of dealing and hardware platforms

周立功的ARM9平台下，实现基本GPIO管脚的操作，很实用-ZLG ARM9 platform, the basic realization of GPIO pin operation, very practical