secondly, we finished the hardware drive programming and called them HAL(Hardware Abstraction Layer). The HAL was used by upper layer user or system.

• 第二步的工作就是完成该开发板上的外部设备驱动程序编写,把底层跟硬件相关的东西做成硬件抽象层HAL(Hardware Abstraction Layer),供上层用户或操作系统调用。