Subversion Repositories svnkaklik

/* compass.c

 *

 * Software to read from the CMPS03 magnetic compass. 

 *

 * By Josh Marshall, joshua dot marshall at studentmail dot newcastle dot edu dot au

 * October 15, 2004.

 *

 * Adapted from code for the SP03 speech synthesiser 

 * By Bram Stolk, b.stolk at chello.nl

 *

 * Bram Stolk's notes:

 * In linux, you can do I2C stuff in user-space, if you enable

 * the device-interface to i2c. You can use plain read() and 

 * write() calls on your /dev/i2c-0 file.

 *

 * NOTE: Check if you have an i2c adapter active by doing:

 * cat /proc/bus/i2c

 * If this comes up empty, then you have no adapters. If the

 * file does not exist at all, you probably lack i2c kernel

 * support alltogether.

 */

#include <errno.h>

#include <string.h>

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <fcntl.h>

#include <linux/i2c-dev.h>

/* Note that the documentation for the compass states its address as 0xC0.

 * However, this includes the low bit which specifies read or write.

 * Linux i2c does not include this bit in this address, so the actual

 * address is 0xC0 shifted down, 0x60.

 */

#define CMPS03_ADDR	0x60

#define I2C_SLAVE	0x0B	/* Change slave address	

/* The important registers on the compass. Internal/test registers omitted. */

#define CMPS03_SOFTWARE_REVISION 0x0

#define CMPS03_BEARING_BYTE 0x1

#define CMPS03_BEARING_WORD_HIGH 0x2

#define CMPS03_BEARING_WORD_LOW 0x3

#define CMPS03_CALIBRATE_CMD 0xF

int main(int argc, char *argv[]) {

   char *end;

   int res,file;

   int error;

   char filename[20] ;

   long funcs;

   int heading_byte, heading_word_h, heading_word_l;

   int bearing_long, bearing_degrees;

   sprintf(filename,"/dev/i2c-0");

   file = open(filename,O_RDWR);

   if (errno != 0)

   {

     switch (errno)

     {

     case EACCES:

         fprintf(stderr,"Run as root? \n");

         break;

     default:

         fprintf(stderr,"Error: Could not open file '%s' : %s \n", filename, strerror(errno));

         break;

     }

   } 

   if (ioctl(file,I2C_SLAVE,CMPS03_ADDR) < 0) {

     switch (errno) 

     {

     case EBUSY:  

         printf("device is busy \n");

         break;

     default:

         printf("Got error: %s \n", strerror(errno));

         exit(0);

      }

   }

   /* Get software revision number */

   res = read(file, CMPS03_SOFTWARE_REVISION,1);

   if (res < 0) {

     printf("Cannot read software revision level \n");

   } else {

     printf("Software revision level: %02x \n", res);

   }

   /* Loop and read from the compass. */

   while (1) {

     /* The heading byte is 0-255 for the 360 degrees. */

     heading_byte = read(file, CMPS03_BEARING_BYTE,1);

     if (heading_byte < 0) { printf("Error reading from compass. \n"); exit(1);}

     /* The high resolution heading is given in two registers, and is 10 * the 

      * heading in degrees, ie 359.9 degrees reads as 3599. */

     heading_word_h = read(file, CMPS03_BEARING_WORD_HIGH,1);

     if (heading_word_h < 0) { printf("Error reading from compass. \n"); exit(1);}

     heading_word_l = read(file, CMPS03_BEARING_WORD_LOW,1);

     if (heading_word_l < 0) { printf("Error reading from compass. \n"); exit(1);}

     /* Combine the two bytes, and get the heading in degrees. */

     bearing_long = heading_word_h * 256 + heading_word_l;

     bearing_degrees = bearing_long / 10;

     printf("Bearing: %d \n", bearing_degrees);

     /* Wait for a while. */

     usleep(200000);

   }

}