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是这样的,(volatile unsigned *)0x1d20000, 是利用c语言的强制类型转换
可以说是将0x1d20000转换为volatile unsigned类型的指针,而这个指针指向的地址
就是0x1d20000(可以想成 volatile unsigned * p = (volatile unsigned *)0x1d20000)),而#define rPCONA(*(volatile unsigned *)0x1d20000)宏定义
就相当于把rPCONA 定义为这个指针的指(可以想成 #define rPCONA (*p);
中和而言可以把这个宏定义语句看成下面两步来理解:
volatile unsigned * p = (volatile unsigned *)0x1d20000;
#define rPCONA (*p);
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