union的实际使用

记录一下，免得忘记：

1、定义一个共用体变量

这里定义一个64位变量 i2creg_rev，然后通过共用体定义两个位变量bits和bits_reverse，通过bit可以访问指定位的值大小，不需要自己再左移右移转换。

bits_reverse是bits的对端转换，是用来处理大小端定义位的，免得取位值时，取反顺序了

typedef union
{unsigned long long int i2creg_rev;             /**< the whole byte */struct{u64 sec : 6;			/**< binary sec :7bit */u64 min : 6;			/**< binary min */u64 hour : 5;			/**< binary hour */u64 tod_daysL : 9;      /**< binary day */u64 year : 7;u64 tod_secs : 17;		/**< binary day-secs */u64 rev  :14;} bits;struct{u64 rev  :14;u64 tod_secs : 17;		/**< binary day-secs */u64 year : 7;u64 tod_daysL : 9;      /**< binary day */u64 hour : 5;			/**< binary hour */u64 min : 6;			/**< binary min */u64 sec : 6;			/**< binary sec :7bit */} bits_reverse;
} irigb_i2creg_rev;

2、使用

先定义一个union变量，然后用i2c去读的值，赋值给rev_time，之后利用union特性，直接可以提取时分秒，年月日了

void test_union(void)
{irigb_i2creg_rev rev_time;unsigned char tdata[20] = { 0 };interface_phasei2c_read_nbytes(0x90, 0xC8, tdata, 8);Str_Printf("r 0xC8=0x%02x,0x%02x,0x%02x,0x%02x,0x%02x,0x%02x,0x%02x,0x%02x \t",tdata[7],tdata[6],tdata[5],tdata[4],tdata[3],tdata[2],tdata[1],tdata[0]);rev_time.i2creg_rev = ((unsigned long long int)tdata[0]<<56 |  (unsigned long long int)tdata[1]<<48 | (unsigned long long int)tdata[2]<<40 |(unsigned long long int)tdata[3]<<32 |(unsigned long long int)tdata[4]<<24 |(unsigned long long int)tdata[5]<<16 |(unsigned long long int)tdata[6]<<8 |(unsigned long long int)tdata[7] );Str_Printf("%d:%d:%d,%d,%d,@%d\r\n",rev_time.bits.hour, rev_time.bits.min, rev_time.bits.sec,rev_time.bits.tod_daysL, rev_time.bits.year+2000, rev_time.bits.tod_secs);//        Str_Printf("%d:%d:%d,%d,%d,@%d\r\n",rev_time.bits_reverse.hour, rev_time.bits_reverse.min, rev_time.bits_reverse.sec,
//                rev_time.bits_reverse.tod_daysL, rev_time.bits_reverse.year+2000, rev_time.bits_reverse.tod_secs);}