Fwd: i2c - Smbus protocol - query

[Abhijit Betigeri]

Hi,

Please help me on this:

I am using the i2c smbus protocol..

from main calling in such a way:

for(i=0;i<len+1;i++)

        buf[i] = (char)(i);

     len = i2c_eeprom_smbus(i2cdev,devAddr,offset,buf,len,0,offset);

     break;

int i2c_eeprom_smbus(

    int file, 

    unsigned short deviceAddr, 

    unsigned char offset, 

    char *buf, 

    int len,unsigned char rd_wr,unsigned char cmd)

{

    struct i2c_smbus_ioctl_data smbusp;

    union i2c_smbus_data smdata;

    

   // struct i2c_msg              i2cmsg;

    int                         i;

   //memset(&smbusp,0,sizeof(smbusp));

   smbusp.read_write = rd_wr;

   smbusp.command = cmd;

   smbusp.size = len;

   smbusp.data = &smdata;

   

   smdata.byte = buf;

   smdata.word = buf;

   smdata.block[0] = len;

   

   if((i=ioctl(file, I2C_SMBUS, &smbusp)) < 0)

    {

      perror("ioctl()");

      fprintf(stderr, "ioctl returned %d\n",i);

      return -1;

    }

    return len;

}

How do I populate these structures and unions:  struct i2c_smbus_ioctl_data smbusp;

    union i2c_smbus_data smdata;

    

here smdata has three fields - can u pl explain the significance of each field..

Kindly throw some light on this..

Thanks

Regards,

Abhijit

[Tavish Naruka]

Hi

On Mon, May 20, 2013 at 2:29 PM, Abhijit Betigeri <abhijitb...@gmail.com> wrote:

    struct i2c_smbus_ioctl_data smbusp;

    union i2c_smbus_data smdata;

   

   smdata.byte = buf;

   smdata.word = buf;

   smdata.block[0] = len;

How do I populate these structures and unions:  struct i2c_smbus_ioctl_data smbusp;

    union i2c_smbus_data smdata;

    

here smdata has three fields - can u pl explain the significance of each field..

union i2c_smbus_data {
        __u8 byte;
        __u16 word;
        __u8 block[I2C_SMBUS_BLOCK_MAX + 2]; /* block[0] is used for length */
                               /* and one more for user-space compatibility */
};

Union is way to access the same chunk of memory as different types, so these three

types __u8, __u16, __8 array are actually overlapped. See this for a better understanding
http://stackoverflow.com/questions/740577/sizeof-a-union-in-c-c

--
Regards
Tavish Naruka

[Abhijit Betigeri]

Ok.. But here in this scenerio what to populate for byte word and block...

Regards,

Abhijit

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