在《NIOS那些事》上看的程序,串行通信一节,有点小疑问
SOP.H中的
typedef struct
{ //接收寄存器
union{
struct{
volatile unsigned long int RECEIVE_DATA :8;
volatile unsigned long int NC :24;
}BITS;
volatile unsigned long int WORD;
}RXDATA;
//发送寄存器
union{
struct{
volatile unsigned long int TRANSMIT_DATA :8;
volatile unsigned long int NC :24;
}BITS;
volatile unsigned long int WORD;
}TXDATA;
//状态寄存器
union{
struct{
volatile unsigned long int PE :1;
volatile unsigned long int FE :1;
volatile unsigned long int BRK :1;
volatile unsigned long int ROE :1;
volatile unsigned long int TOE :1;
volatile unsigned long int TMT :1;
volatile unsigned long int TRDY :1; //准备信号,准备好为1,否则为0
volatile unsigned long int RRDY :1;
volatile unsigned long int E :1;
volatile unsigned long int NC :1;
volatile unsigned long int DCTS :1;
volatile unsigned long int CTS :1;
volatile unsigned long int EOP :1;
volatile unsigned long int NC1 :19;
} BITS;
volatile unsigned long int WORD;
}STATUS;
//控制寄存器
union{
struct{
volatile unsigned long int IPE :1;
volatile unsigned long int IFE :1;
volatile unsigned long int IBRK :1;
volatile unsigned long int IROE :1;
volatile unsigned long int ITOE :1;
volatile unsigned long int ITMT :1;
volatile unsigned long int ITRDY :1;
volatile unsigned long int IRRDY :1;
volatile unsigned long int IE :1;
volatile unsigned long int TRBK :1;
volatile unsigned long int IDCTS :1;
volatile unsigned long int RTS :1;
volatile unsigned long int IEOP :1;
volatile unsigned long int NC :19;
}BITS;
volatile unsigned long int WORD;
}CONTROL;
//波特率寄存器
union{
struct{
volatile unsigned long int BAUD_RATE_DIVISOR :16;
volatile unsigned long int NC :16;
}BITS;
volatile unsigned int WORD;
}DIVISOR;
}UART_ST;
在UART.C中有个语句
UART->STATUS.WORD=0;
说是这个语句对状态寄存器清零了,这是为什么呢?volatile unsigned long int WORD;这个状态寄存器中的WORD定义的是什么意思呢?
还有->是什么用法?C里的吗?
编程能力不好,求指教
此帖出自
小平头技术问答
volatile(非易失的)unsigned long int(无符号长整型)WORD(变量名),这里用了WORD具有迷惑性但WORD的确不是C语言的关键词。
这句话和int i;语法其实是一样的。volatile 告诉编译器对此变量不能做一些特殊优化,必须每次从地址取数。
UART->STATUS.WORD=0;是个简单的结构体和联合体嵌套的一种定义调用方式,仔细翻书,把结构体和联合层层分解,就一目了然了,C的基本用法。
如果有什么好的建议欢迎到博客留言。
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