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385 kakl 1 
/* compass.c
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 *
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 * Software to read from the CMPS03 magnetic compass.
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 *
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#include <errno.h>
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#include <string.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <linux/i2c-dev.h>
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/* Note that the documentation for the compass states its address as 0xC0.
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 * However, this includes the low bit which specifies read or write.
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 * Linux i2c does not include this bit in this address, so the actual
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 * address is 0xC0 shifted down, 0x60.
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 */
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#define CMPS_Addr	(0xC0>>1)
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#define I2C_SLAVE	0x0B	/* Change slave address
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/* The important registers on the compass. Internal/test registers omitted. */
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#define CMPS03_SOFTWARE_REVISION 0x0
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#define CMPS03_BEARING_BYTE 0x1
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#define CMPS03_BEARING_WORD_HIGH 0x2
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#define CMPS03_BEARING_WORD_LOW 0x3
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#define CMPS03_CALIBRATE_CMD 0xF
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void I2C_addr (int Addr)  // vybere adresu cidla se kterym se bude komunikovat
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{
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    if (ioctl(file, I2C_SLAVE, Addr) == -1)
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    {
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        fprintf(stderr, "Failed to set address to 0x%02x.\n", Addr);
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        exit(-5);
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    }
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}
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int i2c_init()   // zinicializuje i2c
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{
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	file = open("/dev/i2c-0", O_RDWR);
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	if (file < 0)
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	{
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		cerr << "Could not open /dev/i2c-0." << endl;
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		return -1;
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	}
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	return 0;
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}
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unsigned char read_azimut_mag()  // precte azimut z kompasu
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{
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    char Buf[3];      // promena pro manipulaci s i2c
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    I2C_addr(CMPS_Addr);
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    Buf[0]=1;
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    write(file,Buf,1);
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    read(file, Buf,1);
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    return (Buf[0]-SEVER);
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}
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385 kakl 61 
void calib()  // kalibrace kompasu
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{
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    char Buf[3];      // promena pro manipulaci s i2c
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    I2C_addr(CMPS_Addr);
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    Buf[0]=15;
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    Buf[1]=0xFF;
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    write(file,Buf,2);
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}
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int main(int argc, char *argv[])
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{
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   char *end;
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   int res,file;
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   int error;
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   char filename[20] ;
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   long funcs;
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   int heading_byte, heading_word_h, heading_word_l;
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   int bearing_long, bearing_degrees;
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   sprintf(filename,"/dev/i2c-0");
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   file = open(filename,O_RDWR);
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   if (errno != 0)
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   {
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     switch (errno)
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     {
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     case EACCES:
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         fprintf(stderr,"Run as root? \n");
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         break;
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     default:
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         fprintf(stderr,"Error: Could not open file '%s' : %s \n", filename, strerror(errno));
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         break;
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     }
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   }
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   if (ioctl(file,I2C_SLAVE,CMPS03_ADDR) < 0) {
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     switch (errno)
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     {
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     case EBUSY:
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         printf("device is busy \n");
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         break;
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     default:
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         printf("Got error: %s \n", strerror(errno));
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         exit(0);
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      }
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   }
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   /* Get software revision number */
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   res = read(file, CMPS03_SOFTWARE_REVISION,1);
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   if (res < 0) {
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     printf("Cannot read software revision level \n");
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   } else {
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     printf("Software revision level: %02x \n", res);
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   }
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   /* Loop and read from the compass. */
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   while (1) {
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     /* The heading byte is 0-255 for the 360 degrees. */
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     heading_byte = read(file, CMPS03_BEARING_BYTE,1);
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     if (heading_byte < 0) { printf("Error reading from compass. \n"); exit(1);}
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     /* The high resolution heading is given in two registers, and is 10 * the
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      * heading in degrees, ie 359.9 degrees reads as 3599. */
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     heading_word_h = read(file, CMPS03_BEARING_WORD_HIGH,1);
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     if (heading_word_h < 0) { printf("Error reading from compass. \n"); exit(1);}
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     heading_word_l = read(file, CMPS03_BEARING_WORD_LOW,1);
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     if (heading_word_l < 0) { printf("Error reading from compass. \n"); exit(1);}
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     /* Combine the two bytes, and get the heading in degrees. */
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     bearing_long = heading_word_h * 256 + heading_word_l;
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     bearing_degrees = bearing_long / 10;
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     printf("Bearing: %d \n", bearing_degrees);
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     /* Wait for a while. */
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     usleep(200000);
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   }
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}