/*******  compass driver  ***********/

#define porth 0x7C00
#define set_h bit_set(0x7e00,0b00000100)

#define pc_low bit_clear(porth,0b00100000)
#define pc_high bit_set(porth,0b00100000)

#define sclk_low bit_clear(porth,0b01000000)
#define sclk_high bit_set(porth,0b01000000)

#define ss_low bit_clear(porth,0b00001000)
#define ss_high bit_set(porth,0b00001000)

#define reset_low bit_clear(porth,0b00010000)
#define reset_high bit_set(porth,0b00010000)

#define read_sdo input_j(1)
#define check_eoc input_j(0)


void reset_compass()
 {set_h;
  poke(porth,0);
  ss_high;
  pc_high;
  sclk_high;
  reset_high;
  reset_low;
  msleep(15L);
  reset_high;
  msleep(5L);}

int read()
  {int i;
   int j;
   int heading;
   
   heading=0;

   sclk_high;
   ss_high;
   msleep(15L);
   pc_low;
   msleep(15L);
   pc_high; 
   
   while(!check_eoc)
    {;}
   
   msleep(15L);
   ss_low;
   msleep(15L);

   for(i=1;i<8;i++)
    {sclk_low;
     msleep(5L);
     sclk_high;
     msleep(5L);}
   
   sclk_low;
   msleep(5L);
   sclk_high;
   msleep(5L);
   if(read_sdo==1)
     {heading=256;}
   
   msleep(15L);
   for(j=7;j>0;j--)
    {sclk_low;
     msleep(10L);
     sclk_high;
     msleep(10L);
     if(read_sdo != 0)
      {heading +=(int)((2.^(float)(j))+1.);}}
   sclk_low;
   msleep(5L);
  
   pc_high;
    sclk_high;
   
   return heading;}



/*************************END*************************/