ARM寄存器另类定义UNION
联合表示几个变量公用一个内存位置, 在不同的时间保存不同的数据类型和不同长度的变量。typedef struct
{
unsigned char no0:1; unsigned char no1:1; unsigned char no2:1; unsigned char no3:1; unsigned char no4:1; unsigned char no5:1; unsigned char no6:1; unsigned char no7:1; } __BIT8 ;
volatile union { unsigned char strack; __BIT8 strack_bit; } @0x00800000; @后面跟上地址，变量strack的地址就是0x00800000;
strack 跟strack_bit共用一个内存空间，即strack |=1<<5 等价于strack_bit.no5=1; 注意必须加上VOLATILE，否则会被编译器优化掉。 举个例子：
#define __IO_REG32_BIT(NAME, ADDRESS, ATTRIBUTE, BIT_STRUCT)\\volatile __no_init ATTRIBUTE union \\{ \%unsigned long NAME; \\BIT_STRUCT NAME ## _bit; \\} @ ADDRESS
__no_init : __no_init 是一个SEGMENT，是给LINKER用的，定义到不初始化的块中去。 ## : ##是标准C语言中的连接符，BIT_STRUCT NAME ## _bit 等价于BIT_STRUCT NAME_bit 。
__IO_REG32_BIT(GPIOA,0x80,__READ_WRITE,_gpioa_bits); volatile __no_init __READ_WRITE union {
unsigned long GPIOA; _gpioa_bits GPIOA_bit; } @ 0x80
结构体_gpioa_bits 定义如下： struct {
unsigned long PA0 :1; unsigned long PA1 :1; ......
unsigned long PA31 :1;
}_gpioa_bits;
调用： GPIOA |=1<<31;等价于GPIOA_bit.PA31=1; #define GPIOA (*((volatile unsigned long*)0x80)) #define GPIOA_bit (*((volatile unsigned long*)0x80))
