I2C Max518

From GumstixDocsWiki

The MAX518 is a dual i2c digital to analog converter.

On the host computer fetch the lm_sensors-2.9.2.tar.gz package.

Extract the i2c-dev.h file from the kernel/include directory and place it in your project directory. There is a minor bug in the i2c-dev.h file that comes with the lm-senors package (related to the I2C_RDWR call). A patched version is available from SVN.

Credit for this codes origins goes to the authors of http://www2.lm-sensors.nu/~lm78/cvs/i2c/doc/dev-interface .

Copy i2cRead.c:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include "i2c-dev.h"

/* Intended to allow the reading of I2C packets to arbitrary addresses */

int main(int argc, char *argv[])
{
    int file;
    int adapter_nr = 0; /* probably dynamically determined */
    char filename[20];

    int i2c_addr;
    int read_bytes;
    char buf[256];

    int i;
    printf("I2CRead system\n");
    if(argc-1<2)
    {
        printf("Usage: i2cRead i2c_addr read_bytes\n");
        return(1);
    }

    sscanf(argv[1],"%x",&i2c_addr);

    sscanf(argv[2],"%d",&read_bytes);

    sprintf(filename,"/dev/i2c-%d",adapter_nr);
    if ((file = open(filename,O_RDWR)) < 0) {
        printf("ERRNO: %s\n",strerror(errno));
        exit(1);
    } else {
        printf("Opened /dev/i2c-%d\n",adapter_nr);
    }

    if (ioctl(file,I2C_SLAVE,i2c_addr) < 0) {
        printf("ERRNO: %s\n",strerror(errno));
        exit(1);
    }

    if ( read(file,buf,read_bytes) != read_bytes) {
        printf("I2C Send %x Failed\n",i2c_addr);
    }

    printf("Addr: %x Data: ",i2c_addr);
    for(i=0; i<read_bytes; i++)
    {
        printf("%x ",buf[i]);
    }
    printf("\n");

    if(file >= 0)
        close(file);

}

Copy i2cWrite.c:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include "i2c-dev.h"

/* Intended to allow the writing of I2C packets to arbitrary addresses */

int main(int argc, char *argv[])
{
    int file;
    int adapter_nr = 0; /* probably dynamically determined */
    char filename[20];

    int i2c_addr;
    char rec_bytes;
    int sbuf[256];
    char buf[256];

    int i;

    printf("I2CWrite system\n");
    if(argc-1<2)
    {
        printf("Usage: i2cWrite i2c_addr i2c_byte1 i2c_byte2 ...\n");
        return(1);
    }


    sscanf(argv[1],"%x",&i2c_addr);
    for(i=2; i<argc; i++)
    {
        sscanf(argv[i],"%x",&sbuf[i-1]);
        buf[i-2] = sbuf[i-1];
    }

    printf("Addr: %x Data: ",i2c_addr);
    for(i=0; i<argc-2; i++)
    {
        printf("%x ",buf[i]);
    }
    printf("\n");

    sprintf(filename,"/dev/i2c-%d",adapter_nr);
    if ((file = open(filename,O_RDWR)) < 0) {
        printf("ERRNO: %s\n",strerror(errno));
        exit(1);
    } else {
        printf("Opened /dev/i2c-%d\n",adapter_nr);
    }

    if (ioctl(file,I2C_SLAVE,i2c_addr) < 0) {
        printf("ERRNO: %s\n",strerror(errno));
        exit(1);
    }

    if ( write(file,buf,argc-2) != argc-2) {
        printf("I2C Send %x Failed\n",i2c_addr);
    }

    if(file >= 0)
        close(file);
}

Compile the code with <path>/arm-linux-gcc -o i2cRead i2cRead.c and <path>/arm-linux-gcc -o i2cWrite i2cWrite.c. Note that you need to FIND arm-linux-gcc first.

Copy the executables to the Gumstix and run ./i2cWrite 2c 00 ff

Place an oscilloscope probe (or multimeter) on the DAC0 output and observe a 5v output on the DAC0 pin.

run ./i2cWrite 2c 00 00

Place an oscilloscope probe on the DAC0 output and observe a 0v output on the DAC0 pin.

Troubleshooting: If the compile fails with i2cRead.c: In function `main': i2cRead.c:40: error: `I2C_SLAVE' undeclared (first use in this function) you have the wrong i2c-dev.h. It should be 12-13k in size and its in the lm_sensors-2.9.2.tar.gz package at the moment.