Structure bit field

[Aswin_5232]

Hi, I am using CodeWarrior 5.2 and the controller is MC9S12DG256B.

When I am assigning each structure element with values and finally reading the overall value using union it is giving different values. how to solve this issue. I think there is difference in byte ordering.

typedef union

{

  unsigned long  w;

struct  {

    unsigned long disp_comp_cal : 2;//0

    unsigned long disp_home     : 2;//2

    unsigned long disp_trips    : 2;//4

    unsigned long disp_fuel     : 2;//6

    unsigned long disp_hours    : 2;//8

    unsigned long disp_service  : 2;//10

    unsigned long disp_diags    : 2;//12

    unsigned long disp_slftst   : 2;//14   

    unsigned long disp_cust_set : 2;//16

  }b;

}attrib2;

[Aswin_5232]

Hi Lama, when I am changing the project settings this issue get resolved but values read from different PORTS are also getting reversed. Any other solution for this. 

[Aswin_5232]

Hi Lama,

Thanks it is working now.

[lama]

Hi,

look into attached file to see solution.

You should think about compiler setup .... look into the help or manuals ... keyword=bitfield.

Your issue is order of bits in the bitfield.

Best regards,

Ladislav

My test code:

#include "derivative.h"      /* derivative-specific definitions */

//******************************************************************************

typedef union

{

  unsigned long  w;

struct  

  {

    unsigned char disp_comp_cal : 2;//0

    unsigned char disp_home     : 2;//2

    unsigned char disp_trips    : 2;//4

    unsigned char disp_fuel     : 2;//6

    unsigned char disp_hours    : 2;//8

    unsigned char disp_service  : 2;//10

    unsigned char disp_diags    : 2;//12

    unsigned char disp_slftst   : 2;//14   

    unsigned char disp_cust_set : 2;//16

    unsigned int  dummy         : 14;

  }b;

}attrib2;

//******************************************************************************

void main(void) 

{

  attrib2 attrib22;

  attrib22.w = 0x00UL;

  attrib22.b.disp_comp_cal =2;

  attrib22.b.disp_home     =1;

  attrib22.b.disp_trips    =3;

  attrib22.b.disp_fuel     =1;

  attrib22.b.disp_hours    =2;

  attrib22.b.disp_service  =1;

  attrib22.b.disp_diags    =3;

  attrib22.b.disp_slftst   =1;

  attrib22.b.disp_cust_set =1;  

  attrib22.b.dummy         =0x3FFFF;  

  // expected 0B1001 1101 1001 1101 0111 1111 1111 1111

  //          0x9D9D 7FFF 

  DDRAB = 0xFFFF;

  //------------------------

  for(;;)

   {

    attrib22.b.disp_comp_cal +=1;

    attrib22.b.disp_home     +=1;

    attrib22.b.disp_trips    +=1;

    attrib22.b.disp_fuel     +=1;

    attrib22.b.disp_hours    +=1;

    attrib22.b.disp_service  +=1;

    attrib22.b.disp_diags    +=1;

    attrib22.b.disp_slftst   +=1;

    attrib22.b.disp_cust_set +=1;  

    PORTAB = (unsigned int) (attrib22.w & 0xFFFFUL);

    PORTAB = (unsigned int) ((attrib22.w >> 16)  & 0xFFFFUL);

   }

  //------------------------

EnableInterrupts;

  //------------------------

  for(;;) 

   {

     _FEED_COP(); /* feeds the dog */

   }

  //------------------------

}

//******************************************************************************