arm的i2c接口读，需要连读2次才可以吗？

只看该作者 · 2011-11-15 13:32

int i2c_read(int reg_offset)
{
int data;
      int activity;
   //       reg_offset = reg_offset | 0x100 ;
// mem_wr_i2c(0x10, reg_offset); // IC_DATA_CMD: set register address
*(volatile UINT32 *)0x18500010 = reg_offset;
// mem_wr_i2c(0x10, 0x100); // IC_DATA_CMD: set read bit
*(volatile UINT32 *)0x18500010 = 0x100;

ic_status = mem_rd_i2c(0x70); // IC STATUS register. LSB is the common activity bit
activity = ic_status & 0x1;
while (activity == 0)
{
      ic_status = mem_rd_i2c(0x70); // IC STATUS register. LSB is the common activity bit
      activity = ic_status & 0x1;
}
data = mem_rd_i2c(0x10); // IC_DATA_CMD: read returned register value
//printf("1:%d\n",data);
ic_status = mem_rd_i2c(0x70); // IC STATUS register. LSB is the common activity bit
activity = ic_status & 0x1;
while (activity == 1)
{
      readCounter++;
      ic_status = mem_rd_i2c(0x70); // IC STATUS register. LSB is the common activity bit
      activity = ic_status & 0x1;
}
   data = mem_rd_i2c(0x10); // IC_DATA_CMD: read returned register value
printf("2:%d\n",data);
return (data);
}

只看该作者 · 2011-11-15 13:34

这段代码，就是i2c状态关闭的时候，从data线读一次：
data = mem_rd_i2c(0x10);
然后i2c从激活状态到未激活状态在读一次，这次的值才真正的返回，这段代码如果把第一处代码注释，
data = mem_rd_i2c(0x10);
程序i2c通讯不正确了。。。
也就是必须读2次，问题是，为什么？？
核心是arm内核